Thursday, June 06, 2013

Tropical Storm Andrea: June 5, Update A

I just learned that there’s a 13 foot python on the loose in St. Petersburg (Florida)! Eeek. Forget the storms, it’s time to “run away, run away!” (quote rather aptly attributed to Monty Python).

Meanwhile, in the Gulf our little blobette is now Tropical Storm Andrea. A plane was sent into the system and found closed circulation this afternoon. <Jargon Alert!> Closed circulation basically means the winds form a complete circle. Easy peasy, huh? <End Jargon Alert!>

At the 10pm CDT (11pm EST) forecast, she was centered at around 26.0N, 86.3W, heading North at 6mph.  Her central pressure is 1002mb, with winds of 40mph.

A Tropical Storm is defined as a storm with closed circulation and winds of 39-73mph.

<Rant Alert!> Great googliemooglies! I can’t believe they named her!! I completely, totally and utterly do NOT agree with giving this system a named Tropical Storm status! When they named her, they said her winds were 40mph…  1mph above the cut off for storms. Since then she has steadily deteriorated (as I will show below). It doesn’t take a genius to figure out that this makes her a mere tropical depression (at the most)! She should never have been named a Tropical Storm!! <end rant alert! (for now)>   

Let’s see what is going on shall we? First, the center is at around 26N, 86.3W. You can see that this is still very much on the western side of the convection in the infrared satellite image, which shows that she still is experiencing strong wind shear. And the corresponding water vapor satellite image shows a lot of dry air to her west. Both of these are inhibiting her development and have been doing so all along.

<Technical Alert!> Satellite Imagery: I mainly use three sorts of satellite images: visible, water vapour, and infrared. The visible one is obvious… it is what you would see if you took a black and white photo. Best used during daylight hours of course! ;-) The water vapor image is also pretty obvious…it shows how much water vapor there is in the atmosphere. Brown areas are dry (think of parched deserts) and any other colour indicates some amount of water vapor. The infrared satellite image is the most interesting though because not only does it show where the storm is, but it also gives us an indication of how strong it is and what sort of weather we have. The colours represent how high the clouds reach into the atmosphere because they are based on the temperature at the top of the cloud (which is what the satellite sees). It gets colder the higher you get in the troposphere (as I mentioned yesterday), so we can tell from cloud top temperature how deep the clouds are and therefore how strong the convection is! The red colours are very big high clouds with the coldest temperatures (other than a dark gray), and blues and whites are lower, warmer clouds. The redder the cloud colour, the more active the convection. My general rule of thumb (having seen these images and lived under them at the same time) is that blue and yellow areas are mostly clouds, with some rain in the yellow areas. But as you get to the orange and red, you get thunderstorms and possible tornadoes (in the red/dark gray areas). <End Technical Alert!>

I pulled the satellite image above (here again) at around 11.45pm but I also have the infrared satellite image that I pulled at around 8.30pm for comparison(underneath the 11.45pm image):

You can already see that the yellow (rainy) area has decreased quite a bit in the last ~3 hours, which indicates that she is weakening. The red patches that you see are over the very deep warm water of the Loop Current (as I mentioned yesterday). All day today this system has been moving over the northern edge of the Loop Current so, as expected, she had quite a bit of thundery weather in her in those areas which did help her strengthen a bit (but not a lot).  As she moves farther north, she moves away from that deep warm water source, and given the wind shear and dry air, she will continue to weaken. I would expect some rain because the sea surface temperature is a balmy 27-29 deg C. She will be more of a rain event than a wind event though, and some parts will get buckets of rain (with maybe a smidgen of thunder), so get your wellie boots out! (especially if you have a graduation ceremony in a field anywhere south of the big bend tomorrow).

As for track… she is moving at a leisurely 6mph. The forecast has her making landfall in the big bend region of Florida. I agree with this (even though I don’t agree with naming her as a Tropical Storm… I thought I’d mention that in case you missed my subtle hints earlier). One thing to watch out for if you are on the west coast of Florida is storm surge, which looks pretty low right now actually. Because the winds move in an anticlockwise direction around a tropical storm, she will be pushing water onto the coast (including into Tampa Bay) in areas south of the center, and pushing water off the coast in areas north of the center. The slower she moves, the more time there is for water to pile up. If you live in the Cedar Key area, if I recall correctly, you are prone to higher storm surge as she passes to the north of you (if she does), so definitely keep an eye on that.

<Technical Alert!> (another Technical Alert in the same entry… time to have a second glass of wine to match. Hmm… I think I may have stumbled across a new science drinking game!! ;-)) To look at the storm surge I use NOAA’s National Ocean Service website, Tides Online: Click on the state you are interested in, and then a location within that state. For example, here is the graph from St. Petersburg:

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 (less than 0.5 ft). The height of the green line gives you the storm surge level.  The graph below that is wind speed and direction. Below that is air pressure, and below that is air and sea surface temperature. <End Technical Alert!>

By the way, as she moves across Florida, and heads north to Georgia and up along the east coast to South Carolina, North Carolina and beyond (all by Friday evening), she will still have rain because she’ll begin to interact with the Gulf Stream. But, given she’ll be a fast moving system, I don’t think she’ll have too much time to organize. And I really think she should be a Tropical Depression at the most, if not just a low by then!   

Time to go sleep now… mutter mutter… Tropical Storm indeed… mumble grumble…

I’ll be back tomorrow with an on-the-ground report on this blobette! (currently it’s raining a bit and not very windy… in fact it is better than the last couple of seasons of British summer weather!).

Night night for now,


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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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