Tropical Depression Isaac, Hurricane Captain Kirk, and Tropical Storm Leslie: August 30, Update A

Goodness me, the title of this post took me half an hour to write! What a smorgasbord of storms we have today. I better open a bigger bottle, we could be here a while… ;-) Here is a pretty groovy infrared satellite image of the north Atlantic this evening that shows all three storms:

Tropical Depression Isaac
It looks like Isaac has just crossed into Alabama, but was downgraded to a mere Tropical Depression before leaving Louisiana, with winds of 30mph, central pressure 998mb. If you look at the above satellite image, you can see that he has very little convection left (the yellow areas are rain no thunder, the blue are mostly thick clouds but no rain). What’s is still impressive about him is that looonnnnggg stream of clouds stretching northeastward across the Atlantic(because of wind shear/ low pressure front) … all the way to the UK!! (not that they’d notice a few more clouds up there). A real trans-Atlantic bridge!

He is currently somewhere around 33.5N, 93W, heading N at 10mph. The NHC have issued their last advisory on him, and I don’t see him lasting much beyond Alabama. Circulation is slowly decreasing, and there is very little convection in him. I read some warning about tornadoes on the NHC site earlier today but I only know the basics about tornadoes so I can’t really assess the potential for them as he moves into the US.

Here are a couple of on-the-ground reports from the northern Gulf. Denise R. said that Lafitte and LaPlace, LA have a lot of flooding. I hear that there is oily foam being washed up on the beaches in Florida, near the Alabama border. And Mike A. from New Orleans wrote this morning “been without power and internet since yesterday noon. Found a bar with generators! Lots of wind & rain but all is ok”. I think it should be mandatory for any bar in New Orleans that is able to serve a Hurricane (the drink) to have a generator!

It looks like the flood-prevention systems of New Orleans held their ground – the levees, floodgates etc. Which reminds me, Gary M. told me today what fish say when they swim into a wall….. dam! (heeheeheehee)

Hurricane Captain Kirk
Saying Captain Kirk was a wimp yesterday was like throwing down the gauntlet, wasn’t it? Having watched all The Original Trek and Baby Trek (the latest movie), I should have known this. He pulled himself together overnight and has had a pretty nice looking eye for most of today – he is now the real McCoy, which must make it quite confusing on a Star Trek set ;-). Here are the latest visible (at night) and infrared satellite images of him:

Just like a young William Shatner, he may be little, but he’s strong, good looking and is (for now) the biggest name on screen.

He is currently at 29.0N, 50.7W, heading NNW at 12mph (warp factor 4). Officially the wind speeds are 100mph, central pressure is estimated to be 980mb. This makes him a Category 2 storm (range: 96-110mp). Although his circulation is actually comparable to Isaac’s, Kirk is not experiencing wind shear.  He has also almost moved out of that dry air to his south, which you can still see is impacting him because the convection is weaker on the southern side.

Kirk will stay out there in the Atlantic quadrant. It looks like he’ll meet up with bits of Isaac and the low pressure front, and may get a bit bigger (and stronger) before being teleported to the northeast.

To mark the first day of DragonCon, it is fitting that Captain Kirk became a hurricane today.  J (Hey, I just read the 11pm advisory and even the NHC have some cool geeks in there somewhere… they wrote ‘ACCELERATE AT WARP SPEED’!! Yay!)

Tropical Storm Leslie
Our little Atlantic Blobette was bumped up a couple of notches during the day today, which is no surprise. I thought she was looking a little strong for a mere blobette yesterday. She currently has winds of 50mph and a central pressure 1002mb, making her a mid-intensity Tropical Storm. She is officially at 14.7N, 46.8W, moving W at 18 mph. I’d say she was closer to 14.4N, 46.8W, but it is night and I can’t quite tell.

The forecast track has her heading WNW tomorrow and then NW on Saturday, missing the Leeward Islands and heading in the general Bermuda direction. I am not sure she will do this yet, so if you are in that northeast corner of the Caribbean, I’d be prepared and keep both eyes on her.  I don’t think she’s done heading westward yet.

Her convection is better than the boys’ at the moment, with thunderstorms and a cloud field that covers the length of the Lesser Antilles. Her circulation is also pretty strong in the lower half of the troposphere and is improving in the upper troposphere.

That’s it for tonight. Tomorrow is the last day of August… we are 1/3 of the way through the busiest part of the season. Oh joy. Where’s that ‘skip-to-the-end’ button?

Night night,
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm
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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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Tropical Storm Isaac, Tropical Storm Captain Kirk, and Atlantic Blobette: August 29, Update A

Well things didn’t go quite as well as one could have hoped for on the northern Gulf coast today. Isaac decided to visit the area for a little longer than is decent really, and stalled for a few hours. I hear that although the levees and other flood-control devices (gates, pumps etc) around New Orleans held (the ones that were bolstered since Katrina – which was 7 years ago today), a levy in the outskirts (Plaquemines Parish) was overtopped with water about 14 feet above normal. There is, of course, a lot of flooding in other places along the Gulf coast. Here is a photo of east Biloxi, MS, (90/Beach Blvd) that I got via Andy F. (thanks!):

If Isaac had passed or stalled east of New Orleans, it would have been a different story because of the angle of the mouth of the Mississippi and the direction of winds. Here is the map of Louisiana from the tidesonline website:

The map is a reference as you look at these water level observations from Shell Beach and Berwick (I grabbed these around 2pm EST):

At Shell Beach (left), on the east side of the eye, the water reached a maximum of about 12 feet above normal.

However at Berwick (right), on the west side of the eye, water levels were approaching 4 feet below normal… combined, that’s a water level difference close to 16 feet between the east and west side of the eye! (thanks to Dennis M. for prompting this discussion earlier today!)  

 

Tropical Storm Isaac

He was downgraded from a hurricane this afternoon (around 2pm). He is now (finally) moving NW at an excruciatingly slow 5mph, and is currently at 30.1N, 91.1W. Central pressure is 977mb, winds are now 60mph. However his impact wasn’t so much in the winds (other than they caused the water to pile up) as it has been in the water and rain.  There are still some strong rain storms (as anyone in Alabama, Mississippi and half of Louisiana will tell us), but they are diminishing… not so much of the tornado-generating storms now, mostly heavy rain.

 

He is forecast to remain a Tropical Storm until he pretty much clears Louisiana, and will then be a tropical depression as he tracks north and then northeast though Arkansas, Missouri, Illinois, Indiana and Ohio. Quite a collection of states! It looks like his progress through Louisiana will be slow so I agree with the downgrade before he leaves the state. At the moment it looks to me like he doesn’t have a lot of room to move very far north and may just fizzle out in Arkansas. Perhaps this will change by the time I see the data tomorrow. The circulation is still very strong throughout the troposphere.

 

Tropical Storm Captain Kirk

Switching gears to the next one out there… we have Tropical Storm Kirk, that shall henceforth be known as Tropical Storm Captain Kirk. He is at 25.3N, 47.6W, heading WNW at 12 mph. Minimum pressure is estimated to be 1005mb, winds are estimated at 50mph, which makes him a weakish TS (range: 39-73mph).

 

The circulation is strong in the lower half of the troposphere but nothing much going on in the upper half (yet). There is not much wind shear but his convection is really pretty wimpy (not an adjective that macho Captain Kirk would approve of!) because he is being caught up in what is left of the dry Saharan Air Layer (SAL).

 

He is forecast to stay in the Atlantic… and boldly go where no man is (hahaha).

 

Atlantic Blobette

Hmm… this one may be one to watch. This blobette’s convection is bordering on the good side because she is on the very southern edge of the dry SAL. her circulation (vorticity) has slowly improved throughout the day, and there is even a signal in the upper troposphere which is a sign that she may blossom into a hurricane when she grows up.  Wind shear is weak, water temperatures are warm… things look good for intensification. Currently the NHC give her a 70% chance of developing into  a Tropical Storm in the next 48 hours… I think it may be sooner than that. She is around 12.5N, 40W, moving WNW at 15mph. I’ll have a look at her future path when she is a Tropical Depression or Storm. The next name is Leslie.

 

Good luck to everyone caught up in Isaac! If you get a chance, let me know how you fared!!

 

Adieu for today,

J.

 

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm
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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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Hurricane Isaac: August 28, Update B

Isaac officially made landfall on the Mississippi Delta, probably just as I hit send on my last post around 8pm EST. I celebrated with some cheese and a glass of wine. In the hierarchy of munchies, cheese reigns supreme.

His center is at 29N, 89.7W, and he’s heading NW at 8mph. Winds are still 80mph, central pressure is 968mb. This fall in pressure since the last update is because it is from aircraft observations and not an estimate. He’s still right at the coastline so he is still over warm water, but I think his convection is finally starting to decrease from interacting with land, although his circulation is still good throughout the troposphere. It looks like he’ll make a ‘second landfall’ near Grand Isle. He will slowly weaken for now because the coast of Louisiana has marshes and bayous and other such watery swampy things… essentially water with a few twigs stuck in there, right? ;-)

I grabbed the water level graph from Shell Beach in Louisiana because it is impressive to see the water level over 10 ft above normal:

This location and Waveland (Mississippi), where the water reached 7 ft above normal, show where the area of greatest surge for this storm. This is because of the angle of the coastline and the angle of the winds as the storm got closer.

That’s all for today folks!

Cheerio,
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm
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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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Hurricane Isaac and TD11: August 28, Update A

Hurricane Isaac
Landfall in Louisiana is imminent! Actually, from the New Orleans radar (http://radar.weather.gov/ridge/radar.php?product=N0Z&rid=lix&loop=yes) and the visible satellite image (below) it looks like he is moving on-shore on the squiggly bit that sticks out into the Gulf (the Mississippi Delta)!

He was officially upgraded to a hurricane in a special 11.20am (CDT) advisory this morning… although I saw an eye when I was watching him at 6.30am (EST) this morning (I had turned on the computer to see what he was up to before I even had a cup of tea this morning. It was quite uncivilized! ;-)). Here is the infrared satellite image of him that I grabbed at that time – - the eye is clearly visible, even though he looks like a half-eaten (orange and red) biscuit (or cookie if you are in the US):

The northern half of him was all dry dry air, with convection only on the southern side, over warm water.

The NHC issued a second special advisory at 6pm CDT (i.e when I grabbed the top satellite image) to let us know that the center was nearing the coast of LA. At 7pm CDT, he was officially at 29.0N, 89.4W, moving NW at 8mph. The NHC increased his winds to 80mph, which makes him a weak-to-middling category 1 storm (range: 74-95mph). Central pressure 970mb.

Although this increase in wind speed is an estimate they made, I agree with it because his convection has improved. Here's the latest infrared satellite image of him, but this time it is a view of the entire eastern side of the US:

You can see three things from this: first, the red areas (and thundery weather) has increased since this morning; second, the dry air is not chopping him in half anymore – the convection has spread around to all sides; and three, Isaac is still causing convection over eastern and central Florida, as well as parts of Georgia and the Carolinas (because of wind shear). The long arm of Isaac!

Given that he is almost half on land, it is unlikely that he will get much stronger. The circulation (vorticity) data I normally look at seems to be a little outdated at the moment, so I can’t see if his circulation has started to deteriorate yet or not.

Now for the surge. Shell Beach in Lake Borgne, LA, is now 9ft above normal and New Canal Station in Lake Ponchartrain is about 3-3.5ft above. Grand Isle (LA) on the Gulf Coast is about 2 feet above, Bay Waveland Yacht Club in MS is 6ft above normal, Pascagoula (MS) and Dauphin Island in Alabama are both 4ft above, and most of Mobile Bay is 3.5 ft above (but it looks like its dropping now). In Florida, Pensacola reached a maximum of 3.5 ft above normal.

Tropical Depression 11
This guy has some circulation in the lowest half of the troposphere, but it is not very cohesive yet. He is officially at 23.8N, 43.9W, moving WNW at 10mph. Winds are 35mph, central pressure 1008mb. There is some decent convection, which looks like it is nearer to 25N, which shows that there is some wind shear impacting this system. They think he will be a Tropical Storm tomorrow. If the circulation improves, this is quite possible. The next name is Kirk.

Good luck to all those who still have to deal with Isaac! (including the east coast of Florida – I heard there was flooding in Stuart, Florida).

I might be back later with the official word on landfall.

Toodles!
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm
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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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Tropical Storm Isaac: August 27, Update B

Today it looked like the east coast and parts of central Florida were hardest hit from Isaac. They had some massive thunderstorms all day (and yesterday), which are finally diminishing/moving offshore as you can see in the latest infrared satellite image of his convection:

With a center about 300-400 miles away, this shows again just what a big boy he is! He was helping himself to the buffet provided by the deep warm waters of the Florida Current/Gulf Stream off the east coast of Florida, which helped to feed that rainy weather. Comparatively, the west Florida coast got off lightly (so far at least) because we were more-or-less sitting under the deliciously dry air that he was sucking up from the south.

This dry air along with continued wind shear and a lack of deep warm water underneath has really impacted his intensification. There are some areas of strong convection near the center, but they are close to/over those deep warm water patches I previously showed in the sea surface height map. I think he was probably a cat 1 storm earlier today (the circulation has really  been very strong throughout the entire troposphere), but the NHC may just have missed the Love Boat with Isaac (you know I had to get a reference in somewhere! ;-)). Given his disorganized and lopsided appearance now, he’s still classified a Tropical Storm (albeit a very strong TS/border-line cat 1). Officially his winds are 70mph, central pressure 979mb (cat 1 range: 73-95mph). As he gets closer to the northern coast, he will also be impacted a little by the land which will also help inhibit his development. But as he is borderline if the conditions improve just a tad overnight I can see them upgrading him to a weak cat 1 storm.

Apparently I wasn’t completely hallucinating yesterday when I said that I thought he’d move north/NW of the center of the cone track today, towards the right edge of the cone – he just took his time doing it. In the past few hours he has been moving more NNW and now his official center is at 27.1N, 86.8W, heading NW at 10mph (I still think he’s moving a little N of NW). The cone only extends to the middle of MS, but if he continues tracking NNW, he’ll make landfall east of New Orleans.  Even though the MS/AL/FL region is outside the cone, I’d still keep an eye on him until tomorrow afternoon.

<Forecasting/data alert> It is really important that we have data on what is going on off-shore so we can make better estimates of wind speed, direction, and even use it to improve forecasting capabilities. There are a number of coastal ocean observing systems around the US that are being developed to provide us with more detailed information on what is going on out there. I’ll try and show you data from some of them when storms pass by. For today, wind instruments from the COMPS mooring array (run by USF) off the west coast of Florida show measurements of almost 13 m/s, which converts to around 28mph (1m/s =  2.24mph). To look for yourself, go to http://comps.marine.usf.edu/ and you’ll see a map of Florida with some markers. Scroll over one of the markers and the latest wind dial and other data will appear on the left. If you want graphs of the data over the last 24 hours or past few days, click on the mooring, scroll down and click on the graph-looking icon next to the data type you are interested in.  The maximum wind speed I see over the past 24 hours is around 16-17m/s, which is around 35-38mph… so not quite Tropical Storm strength. Unfortunately the station that would have been closest to the storm in this array (farthest out from Florida) is not reporting data at the moment due to a lack of funding.

There are also two NOAA/NDBC moorings in the region – one is slightly northwest of this array and is reporting winds of 27 knots, which converts to 31mph (1 knot = 1.15mph) - not Tropical Storm winds. The other is to the southwest and is reporting winds of 37 knots which converts to 42mph, so definitely weak Tropical Storm winds down there.

There are some FAA observations closer to the northern Gulf coast and Mississippi delta. They are recording winds of around 43 knots, which converts to 50mph. It doesn’t look like any of the surface observations we have support a hurricane at the moment. <end Forecasting/data alert>

Also, speaking of useful data… don’t forget to check tidesonline for storm surge info (I wrote about how to do this yesterday – August 26, Update B). At the moment along the northern Gulf Coast I see a maximum of 1 foot above normal predicted water levels. As the storm passed the west coast, water levels rose from yesterday’s 1-2 feet below normal levels to a maximum of 2 feet above. Here is the water level data from St. Petersburg as an example:

That’s it for today. Everyone stay safe!!
Ciao,
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm
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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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Tropical Storm Isaac: August 27, Update A

I heard from a few people yesterday that they were concerned that Isaac is another Katrina, because everyone is showing the path of the two storms, which is similar as they cross the Gulf, and because it’s almost 7 years to the day since Katrina hit. You should all definitely be prepared, but there is a BIG difference between the two… and that’s the position of the Loop Current and associated eddies etc.

(Science alert) The easiest way to see where the areas of deep warm water are is to look at the sea surface height (because in the summer, the sea surface temperature is almost uniformly warm). We have satellite instruments called altimeters that can measure this. As you know, if things are warm they expand and if they are cold they contract. It’s the same for water. If we have an area where the water is warmer over a great depth, it ‘expands’ and is higher on a map of sea surface height compared to an area where the water is colder. When a storm passes over these warm (high) areas, they intensify because they have warm water to churn up from the deep instead of cold water. (end science alert)

Here is a proxy for the sea surface height map with the path of Katrina and her intensity:

You can see the correlation very easily – she got stronger as she went over the warm areas of the Gulf (i.e. over the Loop Current). And here is a map of the sea surface height yesterday:

Isaac is marked with an ‘X’ (this was his location about 2 hours ago, but you get the idea) and I added an arrow to show his approximate forecast track. He is going to be moving over an area which has some deeper warm water, but as he is currently only a strong Tropical Storm and this area of deep warm water is not very big, he won’t blossom into anything like Katrina’s cat 5.

Although he’s passing over some deep warm water, the atmosphere is inhibiting his development for now. It looks like he didn’t completely get away from that dry air to the south and there is some winds shear that you can see the water vapor satellite images. These are inhibiting his development. As he moves farther north, he will begin to interact with land again, so that should also help to keep his intensity in check.

He is currently at 26.1N, 85.3W, heading NW at 14mph, so slightly slower than yesterday. The center of cone forecast track takes him to New Orleans with landfall tomorrow morning as a hurricane. I’m not 100% sure of this, but the track hasn’t changed in the last couple of advisories so I’ll go with the official track – the models are generally quite decent within 24 hours of landfall. I was asked what I thought about leaving New Orleans. I don’t live there so it is difficult for me to advise – I would go with whatever your local emergency managers say because they have the best overall local picture. Although he is not a strong storm, the water is being pushed onshore and is currently about 1 foot above normal (from tidesonline).

More later,
J.
Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm
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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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Tropical Storm Isaac: August 26, Update C

I’ve been eating a banana and chocolate ice cream and analyzing the latest pressure field data. Hmm… tomorrow it looks like Isaac will have a room to move in a slightly more north/NW direction compared to the current forecast center of cone (i.e. the right edge of the cone), which actually brings him a couple of inches closer to west Florida and Tampa Bay. Currently it doesn’t look like any of the computer models show a west Florida landfall, so I think he’ll just slow down a bit more because the high pressure is now developing on his west as well which means he can’t move too much in that direction either.

The NHC say his center is at 24.2W, 82.9W, currently heading WNW at 14mph. I can see this in the radar imagery from Key West, however the main convection is north of this. The satellite imagery is not as clear as to where the center is (it may be a little north), so I’ll go with the radar and NHC location. They kept his winds to 65mph for now, central pressure 993mb, but I think his convection and structure has improved enough in the past few hours to upgrade him to a weak cat 1 storm (range: 74-95mph). This is because he is still over the Loop Current and it’s deep warm water and he has moved away from the dry air. If he does move in a more north/NW direction tomorrow he will move away from the Loop Current a little quicker, so he might weaken again. He still has some wind shear and although the circulation over the entire troposphere is strong it is not as well-structured in the lower half of the troposphere because he is still being impacted a little by Cuba.

Isaac’s future forecast track is very tricky, and will become trickier if he slows down much more or stalls. From the NHC 11pm advisory: “THERE IS AN UNUSUALLY LARGE SPREAD IN THE TRACK GUIDANCE AFTER 24 HOURS.  THE SPREAD OF LANDFALL LOCATIONS ALONG THE NORTHERN GULF COAST RANGES FROM THE TEXAS/LOUISIANA BORDER EASTWARD TO THE ALABAMA/FLORIDA BORDER”. The latest forecast track shifted slightly to the west as expected, but I’d have to say that at this point that shift means about as much as a the collected works of Shakespeare does to a cat. Everyone should prepare, and we’ll just have to figure this out a day at a time (alas!).

More tomorrow morning.

Night!
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm

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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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Tropical Storm Isaac: August 26, Update B

Still a fine British summer day in my part of Tampa Bay - cloudy, sporadic drizzles of light rain, slightly breezy, warm enough not to need gloves. ;-) Meanwhile in the mid-Keys, Lisa T. said at 5.10pm that “the squalls on Friday were worse than what came through today. It is blustery out now but no rain.”

I spent this lollygagging sort of day backing up my computer (and a cheer erupts from the computer manager gallery!) because over the past few weeks my machine has complained at all the work I make it do and is slowly but surely heading towards a break-down. It’s probably not a bad thing to do before a storm, but I’m <ahem> sure <ahem> that you all back-up regularly anyway, don’t you?

Tropical Storm Isaac’s convection improved after my last update, primarily over the lower Keys. There is still some strong convection in the Gulf, just off the Keys, but the planes found that he hasn’t strengthened so the official winds have been decreased to 60mph, central pressure 992mb. This makes him a mid-strength Tropical Storm (range: 39-73mph). He continued more westward than the earlier forecast track and is still in the Straits of Florida, about 40 miles southwest of Key West. His center is officially at 24.2N, 82.3W, moving WNW at 16mph.

He still has wind shear and dry air that are inhibiting him, but he is now over the deep warm waters I mentioned earlier which would explain the increase in his convection that you can see in the latest infra-red satellite image:

He is still interacting with Cuba, but less so than earlier. Consequently his circulation has improved at all levels of the troposphere. With these conflicting impacts on his intensity and development, I think a mid-to-strong Tropical Storm is a very reasonable thing to expect at the moment.  The NHC have downgraded his future intensity forecast and keep him as a Tropical Storm until tomorrow afternoon, when he gets upgraded to a cat 1. I agree with this downgrade and slower intensification… he won’t be over the deep warm water because the Loop Current is only in the southern Gulf at the moment, it looks the wind shear will persist all the way into the northern Gulf, and the upper troposphere is not very conducive for development. In fact, on the current forecast track (which takes him into Louisiana/Mississippi region on Wednesday), there’s a chance that he won’t intensify to a hurricane at all – if he does, I’m still thinking in the weak-to-mid cat 1/strong Tropical Storm range.

BUT… there is one thing I don’t fully agree with at the moment: the track and forward speed. The high has developed across the northern Gulf. He will either slow down, or move west (currently more likely)… so that track may shift even farther west.

For those of you who are looking at the storm surge, go to tidesonline (http://tidesonline.nos.noaa.gov/), click on the state maps link on the left side of the page, click on the state you want, and then the location. For example, at the moment in St. Petersburg the water level is actually about 1 foot below mean low level! This is because the storm winds are, essentially, pushing water out of Tampa Bay instead of onshore. Here is the latest data from St. Petersburg as an example:

The top graph shows the water level. In this graph, the red line is the actual observed sea level, the blue line is what the predicted water level would be because of the tides, and the green line is the difference between the two. The height of the green line gives you the storm surge level (-1 ft at the moment). The graph below that is wind speed (still increasing in St. Pete) and direction. Below that is air pressure (which you can see is still dropping), and below that is air and sea surface temperature. Wind speed is still less than 15 knots (about 17mph) (1knot = 1.15 mph) so we don’t have Tropical Storm force winds up here yet.

Must go… it’s wine-o-clock! I’ll be back talking about dessert as usual… ;-)

Adieu,
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm

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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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Tropical Storm Isaac: August 26, Update A

Up here in Tampa Bay it looks like a perfectly fine British summer day out there at the moment. In the Keys, things are a little damper… from Lisa T. in the Keys around 11.30am: “Just rain in Grassy Key, waiting for squall line”.

Tropical Storm Isaac is officially at 23.9N, 80.8W, heading WNW at 18mph. This is about right by my books. He is well and truly in the Straits of Florida, just north of Cuba and south of the Keys. If you want to look at a radar loop and watch his eye cross the Straits, go here: http://radar.weather.gov/, and then click on the blue circle that is located closest to the area you want to see. In the case of Isaac, click on the radar data from Key West (the blue circle just southwest of mainland Florida). To get the movie loop, on the left side click on the word ‘Loop’ next to ‘Composite’.

As expected, Isaac is moving a little west of yesterday evenings official center of cone track. The official track has now been shifted so he will pass close to or just west of Key West later today. However the rainiest weather is mostly on the north and east side of the storm, so the Keys and south Florida are getting a few bouts of heavy rain and thundery weather. Luckily, although he is crossing the warm waters of the Straits, there is still some wind shear and dry air that is inhibiting his development so I agree with his current designation as a strong Tropical Storm (range: 39-73mph) with winds of 65mph, central pressure 995mb. The circulation has not changed at any level of the troposphere since yesterday, and remains strong in the lower half, so until that convection improves in all quadrants, I really don’t think they should upgrade him to a hurricane. Here is the latest water vapour satellite image of him so you can see the wind shear with the clouds still streaming off to the north and east and the dry air (shown in brown) to the south.

What factors will influence his intensity in the Gulf?

1. Wind shear: at the moment this looks like it will decrease within the next day or so. This will help him to get organized.
2. Interacting with Cuba and Florida: Cuba is having a larger effect than Florida, because that is what his circulation is interacting with and that inhibits his structure from developing. Because of wind shear and dry air, Florida is only really impacting his convection (which helps). So as he moves away from Cuba in the next day, he will have an opportunity to improve.
3. Dry air to his south: As he moves a little farther north, this will have less of an impact. It will also be less important once he gets better organized.
4. Sea surface temperature: The water is around 28-29 deg C, which is definitely warm enough to allow slow intensification.

5. The Loop Current: He is essentially over this already because he is in the Straits of Florida, where this current is called the Florida Current. (If you need a refresher on this and why it is important, check out the science alert here: http://jyotikastorms.blogspot.com/2012/06/gulf-of-mexico-blobette-and-last-word.html). The upper 75-100m of the water is warmer than 26 deg C…. but the good news here is that as he gets closer to the Keys, this gets shallower, and we are lucky because at the moment it looks like the Loop Current is not very far north in the Gulf at all! That’s the biggie in the Gulf as far as intensification goes. There are a couple of warm eddies out there in the northern/western Gulf, but overall I don’t think he’ll be more than a cat 1, if that (depending on the path he takes as he crosses the Gulf).
6. Upper troposphere structure: It did look like there was a chance that this would be a factor in helping him get stronger, but it looks like the conditions for him to improve his upper tropospheric structure is decreasing. (If you need a refresher on what this is, check out the science alert here: http://jyotikastorms.blogspot.com/2012/08/tropical-storm-isaac-and-td-10-august.html)

At the moment it looks like that  high is continuing to build in the northern half of the Gulf. There is room for him to continue to move WNW/NW for the rest of today, but he will either slow down tomorrow from his brisk 18mph forward speed – if he does, that’s a sure sign of high pressure to the north and west of him, or he may take a more westward track (so really, everyone in the Gulf needs to continue to keep an eye on him!). I’ll have to assess his track options again once he has crossed the Keys region.

If you have to evacuate, there are signs that mark out the evacuation route, complete with a plan attached. Here is an example of one of these so you know what to look out for (I got this via Fred G. in Florida):

I’ll be back later! Time for a cup of tea.
Toodles,
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm

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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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Tropical Storm Isaac: August 25, Update B

It was a relatively calm in the world of forecasting today as we all watched Isaac continue on that NW path along the northern coast of Cuba. He didn’t quite touch the coast enough and remained off-shore, so there has been a very slow improvement in his circulation throughout the troposphere in the last few hours. Thunderstorm activity has also improved in the last couple of hours, but it is confined to the north and east. He is still being impacted by dry air and wind shear (as well as interactions with land – Cuba) because there is very little convective activity on the west or south side of the center, as you can see in this satellite image:

His center is officially at 22.1N, 77.2W and he is moving NW at 17mph. I agree with this – and this is also exactly on the center of cone forecast track the NHC have had posted in the past couple of advisories. No wonder it feels so calm! His winds are still 60mph, central pressure 997mb. I also agree with maintaining his status as a mid-intensity Tropical Storm.

The high pressure that the models are basing their future westward movement on is, as expected, developing (which means that it is expanding from the Atlantic back over Florida). Isaac is following the edge of this high pressure (if you want a refresher on what steers storms, check out the <science alert> here:   http://jyotikastorms.blogspot.com/2012/08/caribbean-blob-and-atlantic-blobette.html, and here: http://jyotikastorms.blogspot.com/2012/08/altantic-blobette-and-caribbean-blob.html). He is also being influenced very slightly by low pressure to his southwest, but this is only temporarily helping him move on his current NW track so we are more concerned with the high pressure for the long term track.

The latest pressure fields show me that he will continue on a NW path tomorrow, remaining along the coast of Cuba, pretty much as forecast, as he goes to visit the Keys (maybe now as west as Key West). The problem is what happens after the Keys. The complication in trying to figure out the landfall in the Gulf is that the high pressure looks like it is building up across the northern Gulf. So either he will be forced more westward than the forecast track as he gets close to/passes the Keys, or he will slow down until there is a path for him to move north in some manner. We will revisit this again tomorrow evening, as he approaches the Keys region, because of the fluctuating high pressure field. Do not place any weight on the center of cone from the Keys northwards… the entire cone is a possibility – and maybe even beyond! And be prepared of course!!

There is still some wind shear to his north and over Florida, so his convection is not very symmetrical around the center (see satellite image). This wind shear could help to slow down his intensification as he crosses the Straits of Florida where the sea surface temperature is 30 deg C and the upper 100m is warmer than 26 deg C but, as his circulation is improving, I think something around a strong Tropical Storm/weak cat 1 in the Keys is possible. I will tell you the factors that play into his intensity in the Gulf tomorrow morning… time for a nap now. J

Night!
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm

-------------------------------
DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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Tropical Storm Isaac: August 25, Update A

Aww… Astronaut Neil Armstrong passed away today. A great inspiration, a great achievement, and a great small step for humankind! Thank you Neil. Alas, a major US news network was a little clueless and didn’t check their facts before releasing the story... dear news network: 1. Neil Armstrong was an astronaut, Neil Young is a musician. 2. Neil Armstrong will not be reading your headline, Neil Young may be surprised to read your headline. 3. Neil Armstrong was the first person to walk on the moon, Neil Young had an album called Harvest Moon.

Coincidentally, Neil Young also has a song called “Like a Hurricane”, and so the link has been made…

Intensity: The islands of Hispaniola and Cuba have taken a bit of toll on TS Isaac and winds are now 60mph, with a central pressure of 997mb. This makes him a mid-range Tropical Storm (range: 36-73mph).  The circulation (vorticity) he had in the upper levels of the troposphere before getting to Haiti has pretty much dissipated, leaving him with good circulation only in the lowest half of the troposphere for now. His convection is also pretty weak compared to before he reached Haiti (where 400, 000 people had to bear the rain and wind in the tents they have been living in for the past 2.5 years (!!), after the 2010 earthquake!).

As you can see in the latest satellite image, there are very few strong thunderstorms or tornadoes at the moment (i.e. no red and gray areas):

This reduced circulation and convection keeps him solidly as a Tropical Storm. The other factors that are currently inhibiting his development are some really good wind shear north of Cuba/Bahamas/Florida and dry air to his west. You can see the impact of this in this satellite image of water vapor, with clouds streaming off to the northeast and east:

The sea surface water is a nice warm 30 deg C, but only the upper 50-60m of the ocean has water warmer than 26 deg C  to help him slowly intensify if he didn’t have other things working against him.

Track: I think Tropical Storm Isaac did head slightly more north of NW last night as he crossed Haiti, via Port-au-Prince, and is now on the northern side of Cuba, right along the coast. That portion (crossing Haiti and Windward passage) of the track shifted a little east and north. His official center is at 21.3N, 76.0W, heading NW at 21mph. I agree with the official track that he will continue to move generally NW.

The models are predicting the high pressure to rebuild (I mentioned this as a possibility in my fourth scenario yesterday), which is why the forecast track takes him westward and into the Gulf. They are not quite sure how much it will rebuild yet or where he will be relative to that, hence there is uncertainty in the landfall. At the moment the pressure fields I’m seeing will allow him clear passage to the eastern side of Florida (so he may even make a personal visit to the NHC in Miami), but the models are all in alignment, so I suspect that high will rebuild. I hope to have updated data later this evening.

The best case scenario for everyone in the entire region (Cuba, Bahamas, Florida) is that he continues to skirt that northern Cuban coastline (or moves onshore a bit). This would be the least impact on Cuba and would also hinder his development. At the moment there is also the wind shear and dry air he is dealing with, which means it will be difficult for him to intensify much until he clears Cuba.

I went and bought some more ice cream. Just in case. ;-)

Until later my friends!
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm

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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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Tropical Storm Isaac: August 24, Update B

What a dilemma… vanilla ice cream and raspberries, pretzels with nutella, or wine and cheese? Hmm. It’s Friday. Maybe a light liquid dessert is called for... a yummy bourbon cream perhaps.  

Tropical Storm Isaac
Officially he is at 17.3N, 72W, heading NW at 10mph. Observations from a plane found the central pressure to be 992mb and winds of 65mph, making him a strong Tropical Storm (TS range: 39-73mph). After many days of grumbling, it is so nice to be able to say that I think this is almost absolutely spot on! ;-) (the only thing I’m not sure about is the NW motion… he might be heading more NNW, but that could just be a temporary thing).

Although the wind speed has increased to being almost a border-line hurricane, his convection has decreased. Here are two infra-red satellite images that show the level of convective activity in him – one I grabbed at 3.45pm (EST) and one I just saved at 8.45pm (EST):

You can see the decrease in his convection over the last 5 hours (red is a lot of rain and thundery weather, yellow is just rain, and blue are mostly just clouds). Unfortunately parts of Haiti got a lot of rain earlier (as well as some windy weather), which they really don’t need given that people are still living in tents and they are prone to mudslides! It looks like the rain has lessened for the moment though.

His center is still over water, just south of Haiti, but it seems unlikely that he will get much stronger given the reduced convection. There are a number of reasons for this. He is interacting with Haiti, Cuba, and of course any other landmass that dares to be in his rather large grasp. There is wind shear on his northern and eastern side, and a bit on his south side too. He has dry air on his west, which is also being brought into the system.

The forecast has him crossing the southwest tip of Haiti by tomorrow morning, reaching the southern tip of Cuba by tomorrow afternoon. The track has shifted eastwards, so we are moving towards my earlier scenarios 2 and 3. At the moment the center of the cone track takes him across Cuba, the Straits of Florida, over the middle Keys and into the Gulf. I think this will shift even farther eastward.

The caveat to all of this is that if that NNW movement I’m seeing lasts, then he will make landfall earlier and is heading towards Port-Au-Prince. He will be over Haiti for a little longer before getting over to Cuba, which may result in a decrease in his intensity. And it makes scenario 3 (that he’ll cross into the Bahamas and to the east of Florida) more possible. (N.C., you ready? I’m just saying.)

Tom says that there’s a new equation for conditions on St. Thomas: “When electrical power is on = every ting on de island does be irie”. I understood most of that (be irie? behave?). I completely understood his next message though: “Storm overall did not produce more than about 25mph winds for St. Thomas with heavy gusts coming with rain band squalls when they passed through. Center was misplaced and forced us to be over prepared and worry more. St. Croix lost some power but not all. Center was forecast to be 53 miles south of Stx but it passed over 160 miles south. Heaviest rain was last night but not constant. Still overcast this morning by hardly any wind. Tail of storm still around so more rain most likely to come.”

Lisa T. from the Keys said it was raining there this afternoon. Not quite the outer bands, but kind of connected.

Ah, yes, there is a little blob out in the Atlantic. Convection is ok but terrible circulation at the moment. I’ll report on that when/if it improves.

Oops… my pretzel stick broke off in the nutella jar. Maybe I can fish it out with another pretzel stick. Oops…that one broke in there too. Umm… maybe I’ll switch to something else and get back to my book (The Hunger Games).

That’s all for now folks!
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm

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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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Tropical Storm Isaac and Tropical Depression Joyce: August 24, Update A

Even less time for sloth and idleness today!! Only time for cheesy puffs and coffee for lunch… (it’s one way of losing weight ;-))

Tropical Storm Isaac
Since my last update the Jamaican govt. issued a Tropical Storm watch for Jamaica, the NHC shifted the center southward again, and they adjusted the track to the south and west, no longer going over as much of Hispaniola as expected, and going closer to Jamaica.

I finally agree with their latest center and intensity! I am very happy for them. The storm is now stronger with winds of 60mph, central pressure 1000mb. The center is around 16.3N, 70.8W and he is moving WNW at 14mph. Now that they know it is stronger than they thought, they can reduce the intensity and still keep it a tropical storm. J The intensity should decrease because it is interacting with the islands of Hispaniola and Cuba to the north, but because it is so large, it is also interacting with South America to the south as you can see in this satellite image of the Atlantic:

Now… the track. This is very important for everyone in the northern Gulf, Florida, the Bahamas, and the eastern seaboard so please try and stay awake for the next bit! Although the storm is passing more south of Hispaniola than the official forecast was suggesting yesterday, there is another change in the pressure fields which will allow it to turn NW tomorrow, which will take it to Cuba. However, it currently looks like there is room for it to move NNW, taking it back to my original path of the east coast of Florida/Bahamas. The complication with this forecast is that the high pressure ridge that was keeping Isaac to the south and ensuring the westward track as he crossed into the Caribbean is breaking… You can see this in the satellite image – that front that was over Florida for the past couple of days has now moved across and out to the Atlantic, but is Isaac too far south for it to have an impact is the question. So… some possible scenarios:

1. The storm stays on the current track, crosses Cuba and the Straits of Florida, and then heads up the eastern Gulf of Mexico for landfall in the northern Gulf (probably panhandle). In this case Isaac’s intensity will decrease as he crosses the length of Cuba. He may not even survive as a Tropical Storm by the time he emerges. He will then cross the warm waters of the Straits, but then move over the shallow west Florida Shelf and he will be interacting with Florida. This will limit his intensity. I don’t think he’ll be a hurricane as he moves north, but if he is, he will be weak.

2. The storm enters southern Florida and moves north overland and back to the Atlantic. Again he will have to cross Cuba, which will knock some steam out of him and he may not be a Tropical Storm as he emerges. As he moves over Florida, he will decrease in intensity (once he gets past the Everglades) so he shouldn’t be too strong. Unknown is the future track if he does take this option.

3. He takes a more northward path, he will still interact with Cuba, but not as much as the previous cases, and then he heads over to the eastern side of Florida, possibly clipping the Bahamas. In this case, there is room for him to intensify because he may be over the Straits and then over the Gulf Stream. Again, the intensity depends on the track.

4. And the final scenario is that he is too far south to take advantage of the break in the high and it builds up. In which case he will move NW in the short term, over Cuba, and then maybe back to a more WNW track. Not so sure about this at all. The models haven’t said a peep about the high rebuilding and I don’t see it yet in the pressure fields.

The forecast track may be shifting back to the east to reflect this – we’ll know more by tomorrow morning, when he is supposed to be approaching Cuba. The NHC have repeatedly said that there is significant uncertainty in the forecast at 3-5 days out. But everyone should be keeping an eye on him and where he is when he crosses the vicinity of Cuba.

Tropical Depression Joyce
The sun shed some light on her center of circulation this morning and the birds were tweeting. But it matters not because she’s fallen apart and is now just a low pressure system. The circulation continued to deteriorate and this is my last update on her.

More later!
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm

-------------------------------
DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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Tropical Storm Isaac and Tropical Storm Joyce: August 23, Update B

I’d like to take a moment to reflect on the immortal and wise words etched on the cover of a little book I’ve read called The Hitchhiker’s Guide to the Galaxy: “Don’t Panic”.  I heard things today that make it sound like people in Tampa Bay are expecting a direct hit by a cat 5 storm. Dearie me. Have a cup of tea and don’t watch so much scary TV (I heard from Vickie that some reporter said today that “A hurricane could be certainly on its way to Tampa”…)!  If that doesn’t work, move on to chocolate, or wine and cheese (hmm.. cheese J). It’s good to be prepared – I have my hurricane supplies (ice cream, wine, water, batteries, candles, sunscreen, bug-repellant, ice cream, wine) – but no need to stress before we know what’s what, right?

Tropical Storm Isaac
No matter how hard I try, I can’t find the center of circulation where the NHC keeps trying to tell me it is. At the moment they say it is at 16.7N, 68.7W and the storm is moving WNW at 18mph. They have kept moving his center southwards relative to their previous forecast during the day. Isaac does have a very poorly defined center, but it still looks like it is south of the official estimate. I am going to assume they can see something that I can’t see because I only have night-time images at the moment. If their center is correct, it means that the convection is mostly in the southwest quadrant of the system.

I agree with the WNW movement though. The pressure fields have changed slightly, which now allow him to move in that WNW direction. They have slowly shifted his 5-day forecast track to the west, which takes him over Cuba, away from Florida and into the Gulf of Mexico. Now landfall is projected to be in the northern Gulf (AL,MS, panhandle of Florida) on Tuesday afternoon.  I’m surprised that they haven’t put any warnings out for Jamaica… even on a WNW track, it looks like it will pass close by. I think this westward shift in the long-term track is reasonable, but I wouldn’t be surprised if he skirted the southern side of Hispaniola and passed between Jamaica and Cuba in the short term.  

His intensity has taken a bit of a hit since my earlier post. I really think he was stronger than a weak 40mph TS earlier, but he has dropped back down to something like the official 45mph speed they currently have (central pressure 1002mb). From this satellite image you can see that his structure and convection is not as good as it was earlier (although it is improving again):

The decrease in intensity was because although the sea surface temperature is the same (around 28 deg C), it looks like he passed over a region where only the upper 50m of the water was warmer than 26 deg C. On top of that, there continues to be some wind shear that is impacting his outer edges - you can still see this in the satellite image because the east side is quite messy and the clouds stream off to the east.

The NHC have downgraded his intensity forecast (because his intensity decreased, suggesting he was stronger than 40mph at some point) so he will no longer be a hurricane in the Caribbean. I think this is quite reasonable if he heads towards Hispaniola, making landfall at the border of Dominican Republic/Haiti. Although he has the intensifying factors of the warm water there is also some wind shear and dry air, and as he approaches Hispaniola he will interact with land too. If he doesn’t take that path and stays over water longer then of course he may intensify further. Although they say he will become a hurricane in the Gulf, this is not certain – it really depends on his track in the Caribbean. I’d take the 3-5 day part of the forecast with a big lump of rock salt.   

A NOAA plane has made more detailed observations over a larger area around Isaac now and those data will be fed into the models which (from the NHC) “SHOULD IMPROVE THE ACCURACY OF THEIR FORECASTS FOR THE NEXT ADVISORY CYCLE.” I look forward to seeing that in the morning.    

I heard from Tom on St. Thomas this morning (just before 10am): “wind shifting. now coming from southeast. expecting things to get more intense for a few hours. not too much rain yet but that is usually near center or at tail. power still on”. I assume it all went ok, although it looks like they are still getting a bit of rain.

Tropical Storm Joyce
She did take a more northerly path than the forecast, and in doing so, she went right into some wind shear and some dry and dusty air, which resulted in a spectacular collapse in her convection. This is now being followed by a decrease in her circulation (although she still has some in the lower half of the troposphere). They downgraded her to a Tropical Depression. She is officially at 16.3N, 43.7W, moving WNW at 14mph. Winds are 35mph, central pressure 1008mb. Because she still has some circulation, it is worth keeping an eye on her until she has completely dissipated. It looks to me like she is at around 20N, moving NW. The official track is more NW than WNW, and does take her to Bermuda by Tuesday, but the satellite image shows that her center is already to the east of this official track, so even if she is moving NW, she’ll be east of Bermuda. Maybe I’m missing something because it’s night so I’ll see if it looks any different by daylight, otherwise I’m not sure why they are so far off on the track.

More tomorrow of course, which looks like it will be another crazy packed day. Silly storms. Sigh. ;-)
Night!
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm

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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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Tropical Storm Isaac and Tropical Storm Joyce: August 23, Update A

It’s one of those days. “Distressingly little time for sloth or idleness” as Oscar Wilde might write.

Tropical Storm Isaac
The NHC continued to shift his center southwards, which is a relief to me. I don’t need new glasses after all. J And maybe we’ll get a better handle on the forecast track by the end of the day now.

He is currently officially at 15.6N, 65.4W, heading W at 15mph. Winds are officially 40mph, central pressure is 1003mb. Apparently he is barely a Tropical Storm at the moment with winds that low. However, his convection is still impressive, as is his girth. Here is the latest infra-red (convection) satellite image:

No surprise, but I disagree with the NHC. I think his winds are stronger than 40mph. His circulation is very good in the lower half of the troposphere and it looks like it is improving in the upper half of the troposphere as well. There is very little wind shear near his center, although you can see that there is some because the clouds continue to stream off to the east. There is also good ‘outflow’ (ooh, jargon! ;-) ) – this is that wispy/jagged  toothsaw blade sort of pattern in the clouds that you can see in the image. This is another indication that his structure is improving.  

I am also not convinced by the 15.6N, 65.4W center location. I know they have the planes, satellites, radars etc to look at, but I think it is still south of this, and possibly also a little west of this location. Maybe closer to 15N, 66W. The NHC do say that there are multiple areas of circulation (vorticity), and if I squint I can see what they are talking about. But I have seen that in other storms (and this one has had them for the past few days), so I don’t know why they have not been able to follow his center for the past few days. He is reaching the longitude of Puerto Rico, which was my guiding point for his future track. From the pressure fields I’m looking at, it looks like he will continue westward for longer than the forecast track currently shows, which means he won’t be as near to Hispaniola as thought and they probably won’t have hurricane force winds. I think this almost eliminates one of the three scenarios I had yesterday – I don’t think he will make that northward turn in time to cross Hispaniola and onto the Atlantic side of Florida, but more on this later (when I have time). If he’s not going to interact with Hispaniola as forecast, it also changes his intensity forecast by the way.

Tropical Storm Joyce
She’s been named. Currently officially at 15.2N, 42.2W, heading WNW at 17mph. Winds are a weak 40mph, central pressure is 1006mb. The track currently looks like it is going to be near Bermuda. I’ll look into this one more later, but at a first glance it looks like they have the forecast track wrong for this one. It looks like she’ll be north/east of the current track, passing well to the east of Bermuda. This may change in a day or so as she begins to interact with the outer areas of Isaac, but I’ll have to figure that out more carefully.

More later!
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm

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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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Tropical Storm Isaac and Tropical Depression 10: August 22, Update B

I just drove back from Tallahassee with almost nary a raindrop despite the clouds, unlike the Lesser Antilles. I sure hope no-one went to the Caribbean for a holiday in the sun this week!

Tropical Storm Isaac
The NHC ‘relocated’ his center southward and it is now officially at 15.8N, 63.0W, heading W at 20 mph. Consequently the track has been shifted farther south so it won’t pass quite as close to Puerto Rico as they previously thought. I still think the official forecast track is a little too far north.At the moment I continue to think that his path will be more westward/southern compared to the official track until early Friday, keeping him around the 15-16 N latitude.

After that it is still a tricky call. You can see the low pressure front that is causing all the ruckus in this satellite image of the Atlantic:

It is still over Florida… it’s been there for two days now! The dilemma is whether or not that front will have moved southeastward enough to meet him when he is in the area of Hispaniola/Cuba (in which case he will be whisked across Hispaniola/Cuba and on the Atlantic side of Florida), or will he be south enough to sneak across the Caribbean (westward) and avoid it either entirely (in which case he’s heading to Mexico) or until he is closer to the Gulf (in which case he may be making a visit to the Gulf side of Florida). (I’m beginning to feel like Vizzini from the Princess Bride! “Now, a clever man would put the poison into his own goblet because he would know that only a great fool would reach or what he is given. I am not a great fool, so I can clearly not choose the wine in front of you. But you must have known that I am not a great fool, so I can clearly not choose the wine in front of me.” etc…)

I will be watching his forward speed tomorrow as well as looking for some sign that the front has decided to take a Caribbean vacation!

The storm took a bit of a beating earlier as it crossed the islands, so although the convection is quite impressive and is improving in the Caribbean, his circulation is still a bit messy because he is still interacting with the islands and there is wind shear. The convection has improved because he has moved away from the dry Saharan air and sea surface temperatures are around 28 deg C, with the upper 75-100m of the water warmer than 26 deg C. The center continues to be broad and the circulation (vorticity) in the lower half of the troposphere decreased a bit. Interestingly, the plane found that the winds are actually less than 45mph, but the NHC have decided to keep that for now which is a good move in my opinion. I think he is on track to become a hurricane by Friday morning at the latest (possibly overnight Thurs/Fri). With official winds of 45mph and central pressure of 1003mb, he is a weak Tropical Storm at the moment (range: 39-73mph). BUT … he is a big boy! Attached is the latest satellite image of the Atlantic showing the areas of convection… he stretches across the entire length of the Lesser Antilles! (you can see the wind shear with the clouds streaming off to the east). So all the islands are experiencing something from Isaac. I heard from Tom on St. Thomas at around noon today: “we are finishing up closing shutters today and putting plants in pots under cover...very windy last night and today it is picking up”.

Tropical Depression 10
The-storm-yet-to-be-named-Joyce is officially at 13.8N, 39.5W, heading WNW at 17mph. Winds are 35mph and it has a central pressure of 1007mb. Not much change here really because it is still interacting with dry air and it is also being influenced a little by Isaac. The official track keeps it as a storm in the Atlantic – possibly heading towards Bermuda. I am not convinced that this will be the track yet, but I can’t really identify a good center because she is so poorly formed so I can’t assess this at the moment but I think there’s a good possibility that it will remain on a more westward track than they think. They also forecast it will become a Tropical Storm tomorrow. Despite the little convection it has (as you can see in the satellite image of the Atlantic), it’s circulation has improved in the lower troposphere and it is moving into an area where the upper tropospheric conditions are ‘storm friendly’ too. I suppose it is possible that it will be strong enough to be named tomorrow, but with the poor formation and convection, it’s pretty borderline.

I think I’ll have to watch The Princes Bride again. In my spare time. In December. After this hurricane season.

Night!
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm

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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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Tropical Storm Isaac and TD 10: August 22, Update A

Thank you to John L. for sending me a check for $1M. Unfortunately it is dated April 2002, so I’m not sure if I can still cash it. Bother. ;-)

Tropical Storm Isaac
His intensity has decreased a bit since last night. Convection is still good as you can see in this satellite image of convection with reds and greys meaning lots of strong thunderstormy weather:

Water temperatures (27-28 deg C) are still warm enough to sustain and slowly increase the convection and no change in the depth of the 26 deg C isotherm (still in the upper 75-100m). The Lesser Antilles are getting a dollop and a half of rain and thunder. However his circulation has actually decreased a bit in the lower half of the troposphere since yesterday - indeed a sign that the islands and some dry air is having an impact. Currently his winds are 45mph, central pressure 1006mb.

They moved his center slightly southward overnight to 15.5N but this morning he is officially at 15.9N, 59.3W, moving W at 21mph. I still think he is slightly south of this, at around 15.4N, 59.3W. We might both be correct! The NHC also don’t have a good handle on his center because they think it has become elongated and not very well formed and they can’t really see it from the local radar either. Here is another satellite image (black/white) – can you see his center?

Having a good center is important in figuring out the track and intensity and I think we will see some track adjustments.

<Forecasting alert> Why are the center coordinates important? The way it works is that the center coordinates are entered into the models as one of the initial pieces of information it needs (called <jargon alert> initial conditions). Then the models are let loose (run) and take a few hours to produce the new track (or intensity, depending on the model). And then the NHC takes the latest set of tracks and produces it’s center of cone track, which is why it is shifted a little every few hours. So if the center is slightly off or the plane returns some new data, these get fed into the model and it takes a few hours (sometimes as much as 8 hours) for changes in the track to materialize. Sometimes there is not much shift in the track because the surrounding pressure fields are so well developed that a little change in the initial conditions doesn’t make much difference. However, in this case the pressure fields are evolving, so things will change. <end Forecasting alert>  

The official track has shifted slightly northward as it approaches Hispaniola, with the storm now passing over Hispaniola and eastern Cuba on Sat. and heading to south Florida on Monday, and then up towards the Tampa Bay area on Monday evening. This is the current OFFICIAL track. However, I think this will change. It may even change by quite a lot so I am not worried about this storm hitting Tampa Bay at the moment, but of course it doesn’t hurt to be prepared!  

Track from now until the Puerto Rico region (around Friday): When they figure out his center, if it is south of their estimate then I think he will initially track south of the current forecast track. If it is actually at 15.9N, then the northern track they have is possible.

Track after PR: There is actually a chance that he will remain on a more westward track. I won’t know this for sure for another day (Thursday) because I need to see where and what he does once he crosses the Lesser Antilles (which he is doing now) but I say this because he is following a high pressure and yesterday it did show a break in the Gulf region, but today it looks like the break has gone. If that break re-appears, it gives him a chance to curve to the north so the other possibility is that he will be on the eastern side of Florida, crossing the Bahamas and into the Atlantic. The uncertainty is if and where this break will occur – will it be over Florida?

All these possibilities in track will change his intensity forecast of course. If he is a hurricane over Hispaniola (if), there is a good possibility he will emerge in the Bahamas as a Tropical Storm. If he crosses Cuba and into Florida or the Gulf, there is a good possibility that he will be a Tropical Storm by the time he gets there. If he remains on a more westward track, then he will be a hurricane and may track into the Yucatan and the Gulf as one. The NHC also recognize that the intensity forecast is very uncertain after Friday/Sat. The only reason I can see to keep him as a hurricane as he crosses these islands is that the upper troposphere is currently looking good to allow him to grow … remember the divergence/convergence/ hurricane structure science alert? If not, I cut and paste here (because I’m nice like that)…

<science alert> A storm is a low pressure system at the bottom of the atmosphere (close to the ground). Air flows from high to low pressure, so it flows into the center. We call this low level air flow inflow or convergence (converging to the middle). But if it flows in from all sides, then where can it go? It can only go one way, and that is up. At the top of a tropical storm it has room to flow outwards… so, interestingly, a tropical storm with a good structure actually has high pressure at the top because the air is flowing out horizontally from that point. We call this outflow or divergence. A good storm has low pressure at the bottom and high pressure at the top. But to set this up there has to be ‘room’ around the top of a storm for the air to flow out, which depends on the conditions of the surrounding atmosphere at the top. With Ernesto, it looks like the conditions in the upper troposphere were not good enough to continue setting up the outflow circulation and that suppressed the entire storm from intensifying. You can look at the lower level convergence here: http://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=atlantic&sat=wg8&prod=conv&zoom=&time= and the upper level divergence here: http://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=atlantic&sat=wg8&prod=dvg&zoom=&time=. For a good storm structure, both would show concentric circles. The more (closer and circular) the circles, the better the structure. <end science alert>

So to sum up, pretty much everyone from the northern Gulf to the eastern Seaboard need to keep an eye on this one. The future track is one of the most uncertain I’ve seen in a long time (even Debby to me was an easier call!). Along with the track, the intensity is uncertain.

Tropical Depression 10
This morning they had this with 100% chance of becoming a Tropical Storm in the next 48 hours, so we are definitely looking at Tropical Storm Joyce two or three days behind Isaac! Since then they have upgraded this to Tropical Depression 10. Joyce will depend on what Isaac does so I’m not going to spend too much time on this for now. Except to say that she doesn’t have much convection at all because of dry air, but her circulation is not bad in the lower half of the troposphere. As I said, she will be named once she gets past this SAL region. She is currently at around 12.4N, 36.3W, moving WNW at 16mph. Winds are 35mph, central pressure 1007mb.   

More later!
J.

Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm

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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.
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