Sunday, September 13, 2020

Hurricane Paulette, Tropical Storm Sally, Tropical Depressions Rene and 20, an Atlantic Blobette and a Gulf of Mexico Blob: September 12, Update A

Six storms a blowin', Five chances over 50%, Four already red, Three in the Atlantic, Two Tropical Depressions, and One Hurri-cane... On the seventh day of Christmas... Oh, sorry, wrong season. ;-)  

So, it's a bit busy out there. This week in September is, statistically the busiest in any Hurricane Season but I don't think I've seen quite this many at the same time before! And actually September 10th is the peak day... so it'll all quieten down after this week. Statistically speaking. Here's a figure that shows the distribution of the number of storms throughout the season (taken from data spanning 100 years): 

Hurricane Paulette

As expected, Paulette toppled over into Hurricane territory today, but is a very weak cat 1 with winds of 75 mph (cat 1 range: 74 - 95mph), central pressure 981mb. She is currently at 28.9N, 59.7W, heading WNW at 14mph and on track to get to Bermuda by Monday morning, although the dodgy weather and raindrops will be there Sunday night. The NHC expect her to be weak(ish) cat 2 when she gets to Bermuda with winds of around 100mph. 

She is slowly emerging from the wind shear she's been battling over the last couple of days which will allow her to strengthen. She certainly has a bit of convection, as we can see in this (still quite poor quality - I don't know what they have done to the algorithms but it's been particularly bad this season!) satellite imagery:

She is also over some warm water, so there's nothing there that will stop her from growing... BUT, there is some dry air. You can see both the wind shear with clouds streaming off to the northeast, and the dry air this in the imagery above as well as here:

This is the water vapor in the upper levels of the troposphere and that area of purple and white that is wrapping around to her north is the drier air. It's even more obvious as you go to the lowest regions of the troposphere:

So, if anything will help to keep her in check, this will be it if it can continue to wrap around and into her center - that's what we want to watch for in the next 12-18 hours. 

Her circulation is very strong in the lower half of the troposphere, and there is some in the upper troposphere as well although it's not quite contained as we see with stronger hurricanes, but she is definitely a hurricane.

Remember: listen to your local emergency managers - they know the lay of the land. And we generally say run from the water, hide from the wind - if you are in a flood-prone area, move inland or to higher ground if you can. Otherwise, hunker down. (This also applies to Tropical Storm Sally folks - especially if she brings water to New Orleans, of which parts are below sea level anyway). Be well out there! 

Tropical Storm Sally

Our Tropical Depression 19 is now Tropical Storm Sally and has crossed the very southern tip of Florida and is in the Gulf. She did track a little south of the forecast yesterday as she crossed Florida, but the eventual landfall end is still the central northern Gulf coast on Tuesday. She's at 26.7N, 83.4W, heading WNW at 8mph. 

It looks like she brought some rain to Florida today and will continue to do so tomorrow...

Winds are now 45mph, central pressure is 1003mb, which makes her a weak Tropical Storm (TS range: 39-73mph). Her circulation is strong in the lower half of the troposphere, in keeping with a Tropical Storm - although it's a little elongated in the middle level which indicates a weaker system because the vertical storm structure is a little wonky (technical jargon for 'wonky' ;-)). Here's the vorticity (circulation) map for the lowest level (850mb) and you can see all the storms marked: 

Here's the one from the middle level (500mb):

And here's the one from the upper level (200mb) for completeness:

She will be moving over water that is warmer than 29 deg C as she crosses the Gulf, so certainly enough to keep her fed, and as she moves away from Florida, the upper ~75-100 m will be warmer than 26 deg C. So the ocean won't inhibit her from slowly growing. There is also very little dry air in the atmosphere. The one thing she is battling is wind shear at the moment, which we can see as the convection is to the southeast of the center and some clouds are streaming to the southeast as well, but that looks like it will subside soon. It looks like her center may be a little south of the official location from the satellite imagery and the vorticity maps, but that could be because of this wind shear. To sum up, she will gradually get stronger as she moves farther into the Gulf. The NHC forecast her to be a mid-sized cat 1 at landfall. 

Tropical Depression Rene

I know I wasn't going to mention Rene again, but this one is just for the records. He's a Tropical Depression at 25.3N, 46.4W, heading NW at 13mph. Winds are only 30mph, central pressure is 1011mb. This time this is really the last note on him. 

Tropical Depression 20

This was the Atlantic Blob from yesterday. It's at 11.9N, 34.6W, heading WNW at 10mph.

Winds are 35mph, central pressure is estimated to be 1007mb. There is pretty decent circulation in the lower half of the troposphere, but I also see some circulation in the upper levels as well from the vorticity maps above. This indicates that he's already a Tropical Storm, but not quite a hurricane yet because the structure in the lower troposphere is elongated and still connected to the Atlantic Blobette (see below).  

Tomorrow this will be Tropical Storm Teddy (Bear). I don't think Teddy is a full first name... isn't it a nickname for Edward or Theodore? Anyway, they can't use Theodore though because it used to be on the list of Tropical Cyclone names and was retired after the 1993/94 season, when it was a cat 5 Cyclone with winds of 130mph (which we would consider a borderline cat 3/cat 4 Hurricane) that hit Papua New Guinea, the Solomon Islands, and New Caledonia in February of 1994. And they can't use Ted either because that was also retired following the 1976/77 season when it hit Queenland, Australia as a category 4 Cyclone in December on 1976 with winds of 115mph (which would be a weak cat 3 Hurricane). So, Teddy Bear it is I suppose. 

Atlantic Blobette

Hanging out just around the Cape Verde Islands at 15N, 24W, this blobette has a 50% chance of developing into something. It's moving WNW. As you can see from the vorticity maps above, there is some circulation in the lower half of the troposphere, but it's still attached to TD 20 and not as strong, so it's not quite at Tropical Depression level. There is some convection, as you can see from the satellite imagery below, and not much wind shear at the moment, so we'll see how quickly this becomes a TD. 

Gulf of Mexico Blob

This little yellow marker only has a 10% chance of development in the next 48 hours. There isn't any convection to speak of and the circulation is only in the very lowest levels of the troposphere, so this isn't even actually a bunch'o'clouds. I won't mention this again unless it looks like it'll develop into something. 

Phew. Don't know about you but I'm gonna need more ice cream... and cheese and wine... 

Ciao for now,


Twitter: jyovianstorm

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 local 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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