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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Yep. But it looks like we'll be ok with this one. :)
I'm good, tomorrow will be fun when my friend in TX wakes up to TD4 in the gulf after 3 days or so of "no storms in the gulf" from him, while I said, "it's coming." I love this blog a little more every time. How's things in your corner of the world?
Hurry before he edits it! lol
I said it was a TD.....
:) - ok off to bed. check back tomorrow...oh wait , it is tomorrow....:)
LMAO at your ignorance!!
Your funny.
I'll take the NHC's advice...not saying you aren't right, but....
What about the SN...can't think of his name...who said the GOM was clear the rest of 2009!
200 miles off shores its crazy......LOL...i put that update together as fast as i could i was watching football and baseball and after they was over logged on and wammy......i haven't been on since 8am yesterday morning...when i did a quick update on this system telling all it was developing....if you read my blog!...LOL
WTH?
lol
his meds must have worn off
Classic clip. Better save that.
The center is a good 50 miles from the convection. Its pretty pitiful right now.
Well since you mentioned baseball, I can't help but brag that a little league team from my hometown is headed to the LLWS for the 2nd time in 3 years! Perhaps y'all should start recruiting future baseball players in GA?
he is talking about Bill I think
I gotcha, okay, I apologize! Well that sure as hell makes more sense now with the radar showing a much more organized system than the QuikSCAT showed. I'm guessing then that it's in the process of dropping that mid-level circulation to the surface, but the data from the buoys, (Which stopped reporting at 1:48 am) indicates that it hadn't yet reached the surface as of then.. However, it looks like the radar presentation has improved over the last few hours (Even some banding features initiating to the East and NE?!), so I wouldn't be surprised to see at 5am, or the next QuikSCAT, that the circulation has finally dropped to the surface in the past 6 hours or so.
What is interesting is that the OHC increases as it moves NW, which gives even more credence to the likely prediction that this could strengthen rather quickly in the next day or so.
This may have a good 24 hours over water unless it turns NNE to NE, which seems unlikely.
Bill has some dry air spinning on its NW side, so I dont see a hurricane until that dry air is moistened up
Perhaps she should've been named Monica?
Oh okay.
agreed
LOL..I think WS lives in South Florida so he'll probably need to take American...
i dont see any dry air but a strengthening tropical storm.
You could be a stormchaser like Mike Theiss and go after them yourself :)
Zing!
cha-zig! lol
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