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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Interesting. Bill is still one to watch for the Leeward Islands, Bahamas, and the East Coast.
TD4 hasn't been named Claudette yet
@8:30am Eastern
2009 Storms
All Active Year
Atlantic
green ball04L.CLAUDETTE
green ball03L.BILL
green ball02L.ANA
East Pacific
green ball10E.GUILLERMO
Central Pacific
West Pacific
green ball95W.INVEST
green ball94W.INVEST
green ball01C.MAKA
Indian Ocean
Southern Hemisphere
As for NNW, please. No model had him moving NNW until five-seven days from now.
OHC (from yesterday)
Let the turn vs wobble debate begin!
Link
I know, theres a big burst of convection that formed where the exposed center was.
Long time no see! Glad you are home to help the family. Really don't expect too much, but I'd rather be READY than to be caught off guard.
Yeah, this one is for the fishes.
I said yesterday the GoM was making me uneasy and I wasn't lying. I was wrong with almost every prediction last year, but have so far been right with almost every prediction this year.
Ummm...wouldn't the meteorologists at the NHC...you know, the ones with the Doctorate in meteorology...pick up on that and reflect it in their forecast and/or discussion?
Don't jump to conclusions that quickly
where you from?
Cane, those waters are HOT and I mean HOT, and TD4 is small. We could see a Humberto. They thought it was going to be 'nothing more than a thunderstorm'. Than wack! Category 1 landfall.
Link plz
GOOD WARNING!
X2 It must be on that path for 3 hour for it to even be considered a change in direction. I am staying off the blogg till tonight. Let the battle begin!
I don't have it. Either its on the backup site or he was making it up to mess with us.
Thanks.=
Unfortunately, Bill may be this year's Katrina or Andrew, in damage terms.
He definitely looks impressive already and covers a large area.
That's what I'm thinking. Trochoidal motions. "Because of this effect, forecasters use a longer term (6 to 24 hours) motion to help forecast tropical cyclones, which acts to smooth out such wobbles." (see link for source)
No update on Sunday. I think it is because of church or something...
I'll have an update Sunday.
Jeff Masters
Bill looks like it will go NE of the islands and be a threat to Bermuda.
TD4/Claudette ?, looks like a rainmaker for the panhandle. Maybe some gusty winds.
i've had a look at both sites and still has 04L .Four
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