Ana and TD 3 take aim at the Lesser Antilles
Tropical Storm Ana was born this morning, when the remnants of Tropical Depression Two made a comeback and organized into the first tropical storm of the 2009 Atlantic hurricane season. Ana is the latest first named storm of the season since Hurricane Andrew got its name on August 17, 1992. The two storms have some similarities, as Andrew formed in the same part of the ocean, and also struggled in its early days with high wind shear and dry air. Let's hope the similarities end there.
Ana is struggling this afternoon. After an modest burst of heavy thunderstorm activity prompted NHC to upgrade Ana to a tropical storm early this morning, Ana has run into strong upper-level winds from the west that are creating high wind shear. This shear was not forecast, and it is not clear how long it will last. The shear has acted to drive dry air into the core of Ana, destroying almost all of Ana's heavy thunderstorms. The low-level center of the storm is now exposed to view, something that often foreshadows the death of a storm. It is possible the shear will destroy Ana, and several models (the GFS and ECMWF) forecast this may be the case. However, the shear forecast calls for shear to drop into the low range, 5 - 10 knots, tonight through Tuesday. If the shear does drop as forecast, Ana should be able to moisten the atmosphere around it sufficiently to protest itself from the dry Saharan air that surrounds it (Figure 1). SSTs are 27°C today, and will increase to 28°C by Sunday. By the time Ana moves into the Bahamas, total ocean heat content rises steeply (Figure 2), and rapid intensification of Ana is possible, if the shear and dry air haven't disrupted the storm. The intensity forecast models, for the most part, predict a steady intensification of Ana to the threshold of hurricane strength five days from now. The HWRF model is on the strong side, predicting a Category 2 hurricane. The GFDL predicts a weak tropical storm five days from now, but that is because the model has Ana passing over the rugged terrain of Hispaniola, something the other models do not predict. In summary, the intensity forecast for Ana has higher than usual uncertainty, and I give equal chances that the storm will be a hurricane--or non-existent--four days from now.
Figure 1. Water vapor image from this morning showing the large area of dry, Saharan air surrounding Ana, and lying to the north of Tropical Depression Three. Image credit: NOAA/SSD
Tropical Depression Three forms, could be Bill later today
QuikSCAT data from this morning and satellite loops revealed that the tropical wave (90L) in the middle Atlantic has finally developed a well developed surface circulation and can be classified as Tropical Depression Three. Recent satellite imagery suggests that TD 3 may already be Tropical Storm Bill. Water vapor imagery (Figure 1) shows that TD 3's center consolidated a few hundred miles south of the dry air of the Saharan Air Layer (SAL). Thus, the storm should not be affected by dry air and dust as much as Ana has been. Ana may also act to moisten the atmosphere in front of TD 3, helping protect the storm from the SAL as it edges farther north over the the three days.
Figure 2. Heat content of the ocean, in kJ per square cm. Oceanic heat content steadily increases for Ana and TD 3 as they approach the Lesser Antilles Islands. Oceanic heat content levels of 90 kJ per square cm are frequently associated with rapid intensification of hurricanes. Image credit: University of Miami.
Wind shear is moderate, 15 knots, but is forecast to fall to 10 - 15 knots on days 2 - 5. Sea Surface Temperatures are about 27.5°C, and will remain in the 27.5 - 28°C range the next five days. The combination of low wind shear and sufficiently warm SSTs should allow TD 3 to intensify steadily, and I expect the storm will be at hurricane strength by Wednesday, when it will be near the northern Lesser Antilles Islands. Most of our reliable intensity models strengthen TD 3 into a hurricane by Wednesday. Oceanic heat content (Figure 2) increases sharply just before the islands, so TD 3 could be intensifying rapidly as it moves through or just north of the Lesser Antilles on Thursday. TD 3 consolidated farther south than expected, so the track models calling for a more northerly path were probably incorrect. In particular, the ECMWF model, which had TD 3 turning sharply northwestward and missing the Lesser Antilles Islands, was probably much too far to the north in this morning's 00Z run. TD 3 will probably pass very close to the northern Lesser Antilles islands on Wednesday and Thursday.
I'll have an update Sunday.
Jeff Masters
Reader Comments
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StormW's latest Blog
I'm just basing what I said off the models. If they change then they change.
got it triple clipped and strapped and foamed in all the really long screws ! house is old though..and your welcome Fisky !
What the heck
Every one take a look at Bill's 18Z Models. How the heck is Bill going to go straight NW from its current position. It's not even going west.
These models need to wake up and smell the roses.
Wiki's just sayin....
lol we'll being seeing major shifts come tomm
that wasn't nice
91L Tampa Radar
Increasing vort on the 0000UTC frame...
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Bill looking impressive:
Yeah.
many college degree people look down on military trained people, no matter what kind of training they get while they are in the military. i know a lot of military trained people who know as much or more then a civilian.and the coast guard has an more invested interest in the weather considering what they are tasked for. if stormw makes a mistake, it could cost lives.
WOw- thanks Aussie - he is staying busy!
Bill still looks like a smiley face..
I am in gulfport.. I also hope you are wrong!
Any experts here think it has time to develop??
456, do not know if you saw my post earlier, but I am glad you are prepared for whatever Ana and/or Bill may bring.
Clarification please? I do not understand what you mean by "really stepped it up"
yea I agree.. also if bill is turning NW immediately due to a weakness in the high, then why is ANA forecasted by the models to track W to WSW?
In any case, models are spreading a bit for ana, and still in consensus that BILL is turning into a fish storm despite its continual W-WSW movement. Although two models anticpate it moving over the northern antilels.
Quoting mobilegirl81:
Gulf coast, do not be surprised what you wake up to in the gulf tomorrow.
Girl I so hope you are wrong
gotta feeling your right ....been watching this all day also...people around here will freak...
got it triple clipped and strapped and foamed in all the really long screws ! house is old though..and your welcome Fisky !Stormbottom, you are good ta go! My house is old too, about 100yrs old. But that's how I like'em.
It's not going west? is it wsw?
I read alot on this blog in June/July about how we would most likely not see any Cape Verde storms this year and that most activity would for above 20N. We now have Ana, Bill and the wave train looks good coming off of Africa.
My question is, what weather dynamics changed in August to allow the Cape Verde season be active? thx
UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 7.2.3
Tropical Cyclone Intensity Algorithm
----- Current Analysis -----
Date : 16 AUG 2009 Time : 011500 UTC
Lat : 11:16:17 N Lon : 36:09:47 W
CI# /Pressure/ Vmax
3.2 / 997.6mb/ 49.0kt
Final T# Adj T# Raw T#
(3hr avg)
3.2 3.4 3.4
What happened with the Tux picture? I actually miss that one.
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