Subtropical Storm in the NE Atlantic

By: Levi32 , 7:45 PM GMT on June 01, 2009

UPDATE 8:15 EDT:

The NHC has recognized the system, but for some reason has not named it yet, despite clear evidence that the system meets STS criteria, and has met it for at least the 6-hour minimum that the NHC likes to see. They are inconsistent in this area so there is no way to know. The invest will not be able to maintain itself for much longer due to cold SSTs.

000
ABNT20 KNHC 012355
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT MON JUN 1 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

A NON-TROPICAL AREA OF LOW PRESSURE LOCATED A COUPLE HUNDRED MILES
NORTH-NORTHEAST OF THE AZORES ISLANDS IS PRODUCING WINDS TO NEAR
GALE FORCE. SHOWERS AND THUNDERSTORMS ASSOCIATED WITH THE LOW HAVE
BECOME A LITTLE LESS ORGANIZED DURING THE PAST FEW HOURS. THIS
SYSTEM IS EXPECTED TO MOVE NORTHWARD OVER COOLER WATERS DURING THE
NEXT DAY OR TWO. THERE IS A LOW CHANCE...LESS THAN 30 PERCENT...OF
THIS SYSTEM BECOMING A SUBTROPICAL CYCLONE DURING THE NEXT 48
HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER BROWN
---------------------------------------------------------------------------------------


We got a surprise to start off the 2009 Atlantic Hurricane Season! The SSD just put up an "invest" floater on a 1002mb extratropical system in the NE Atlantic centered around 24W 40N, just north of the Azores. This system has become warm-secluded (part warm-core), as seen in the phase diagram and satellite image below:





You can see the sub-tropical characteristics associated with this system. Shallow thunderstorms have formed into symmetrical bands rotating inward towards a warm "eye" at the center of the system. QuikSCAT shows a well-defined secondary wind field at the center of the system with tropical storm-force winds. This system bears great resemblance as well as location to Hurricane Vince of the 2005 hurricane season, although Vince was fully tropical.

What precipitated this rare event was probably the system getting cut off from the main westerlies and becoming a closed upper low over the NE Atlantic with the frontal structures spread out quite far from the center of the storm. The system is over water temperatures less than 20C, and hence thunderstorm activity is shallow, but we've seen things like this happen before and we know that it is not impossible. The low will move slowly towards the north and then northeast during the next couple days before the GFS forecasts it to dissipate. This system, by all definition, deserves to be named Sub-tropical Storm Ana, but we'll see whether the NHC decides to be weird or not. Enjoy this awesome storm =)

We shall see what happens!



Visible Loop of the sub-tropical storm (click image for loop)


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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4. shoreacres
3:36 AM GMT on June 03, 2009
Hi, Levi,

Believe it or not, I may have found a link for you that's not in your list! It's the Weather Graphics site.

At the top of the home page there's a link to an interesting analysis of the AirFrance 447 flight that went down.
Member Since: December 31, 1969 Posts: Comments:
3. Lank
1:30 PM GMT on June 02, 2009
Hi Levi! Haven't been here in a while, but I figured that with the season beginning yesterday you would be casting your eyes southeast. Glad you are on the case. I'll be checking in on your prognostications.

Have a great day!
Member Since: December 31, 1969 Posts: Comments:
2. wxgeek723
1:22 AM GMT on June 02, 2009
Interesting you point it out, but I do not think the NHC will bother. It's in the middle of nowhere after all, and even if it deserves a name now, it probably won't in another 18-24 hours. Nice update though!
Member Since: December 31, 1969 Posts: Comments:
1. SevereHurricane
8:07 PM GMT on June 01, 2009
Good Update! :)
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About Levi32

Masters student in tropical meteorology at FSU. Raised in Alaskan blizzards, but drawn toward tropical cyclones by their superior PGF.

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