Friday, May 08, 2015

Subtropical Storm Ana: May 8, Update A

Well here we go again! JDearie me, this is a bit early to come out of hibernation isn’t it? Three weeks before the season is supposed to begin. I haven’t even had my morning cuppa tea yet! What was Mother Nature thinking? Yawn (ok, who else yawns when you read ‘Yawn’? ;-)).

Little miss Subtropical Storm Ana is out there, swirling away at 31.5N, 77.3W, currently with a central pressure of 1001mb and winds of 45mph, which makes her a weak tropical storm (TS range: 39-73mph).  Although she looks like a fierce little thing in the visible satellite movie:
Her bark is worse than her bite because she doesn’t have a lot of convection, as you can see in the infrared (IR) satellite movie:

I’ll explain satellite images properly later (once I’ve woken up J), but basically the convection is all to the south and east of the storm at the moment and the yellow/orange areas are the areas where it’s actually raining (with some heavy rainfall and possibly thundery weather in the orange).

She is stationary at the moment, and the NHC forecast track shows landfall in the Carolinas on Sunday:

I think this is reasonable. There is a high pressure system in front of her which is why she is stationary at the moment.

By the way, she’s called a subtropical storm because she’s essentially a hybrid - the circulation (vorticity) in the lower half has the characteristics of a tropical storm and the upper half of her is like a low pressure front. We often see these early and late in the season, when fronts are still rolling through. It looks like she is continuing to evolve though, and may eventually just be a tropical storm. And in case you are worried that this early storm is unusual or it’s a harbinger of a tough season ahead…abide by the words on the cover of the Hitchhikers Guide to the Galaxy and “Don’t Panic!” ;-)

<Science Alert!> Ooh… first one of the year! Oh lucky day! J It’s not unheard of to have storms this early and especially storms that pop up so close to the coast, but the good news is that they are generally dinky little things that usually bring that much needed rain. Here is a figure that I made a few years ago that shows the track of all storms from 1851 to 2005, divided into the month they formed/existed (graph credit: MOI!).
In the early and latter parts of the season we have storms that develop in the western Atlantic/Gulf of Mexico/Caribbean region. But early in the season things are still warming up and because they are so close to land, they don’t usually have time to develop. During the peak months it’s another story! Storms develop in the eastern Atlantic and have lots of space and time (but no TARDIS, thankfully!) to get nice and strong before getting to land. This figure also shows why we have a ‘hurricane season’. 97% of all storms form between June 1 and Nov 30, with 78% forming during the peak months of Aug-Sept-Oct (stats from Landsea’s 1993 paper). But you can see that every so often we do get storms that develop outside of the season (including January!). Not common, but definitely not impossible! <End Science Alert!>

I’ll send out another update later or tomorrow – after a civilized cup of tea. J

Toodle pip!

p.s. Just a marker for my own reference… thanks to the ~6000 hits on the website since my last post in November, the current count is 88, 406!

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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.

1 comment:

John Sexton said...

Welcome back from hibernation...