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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Yea I am tracking with you I see it.
Its done!!!!
ANA
TD3
91L
Ship at 25.70N 83.10W reporting 8kt winds from 230 degrees.
Tampa...if this is the link you used...you're looking at ocean current vectors, not atmospheric winds.
Tropics anyone without hyperbole or me antics?
Dr. M, do you hear us?
I agree.
Possibly. It doesn't look to be intensifying.
The rotation is really tight. It is in its really early stage. Those east winds to the east of the storm is kinda feeding your convergence zone. There is a south wind to the south as well feeding into the center of where the circulation is forming. That is just my opinion. It also is hard to overlook rotation that you can see on radar. You can see the tight spin around where I would expect the center to be. Winds are too light for TD status at the moment. I would expect the next surface anal to have a low there.
maybe its you who's spinning!
(takes out breathalyzer)
You are correct that is ocean SURFACE currents.....which a SURFACE LOW will show up...
Bill is going to be a fish (recurve far away from the CONUS)
Blob in the gulf will just be a rain maker
BOY, the tropics are exciting!!!! *yawn*
While I agree with that quote, each year they do seem to get a little better. I think you can go out to 5 days now but still need some minor adjustments after day 3.
no keep that is about 5hrs or so old it has not been updateing
thank you
I do too, but it has no east to west winds on the north end...the one type the RUC did see. That is nonsensical. If any part should be there, it is that one.
Oh, and I know why. Turn off the 25 hour average, which I think you can agree is bulls*** for this application and you see nothing at all.
ok first of all who are you? second of all you have no right to keep telling someone to go way. this is about the 10th time i have seen you say this.
you are now officialy the first person on my ignore list ever
yeah, I don't know. It may do the north thing, but I am leary....
Models take ana to its death over the caribbean.. some shitfting north, oh well im going to sleep im starting to lose interest in these systems
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