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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I agree Taz...conditions do seem favorable...just no pressure drops as of now
Maybe not, but that looks ike an eye forming.....?
something about being puerto rican and this model forecast doesnt like it :/
Hey storm i just looked at the nhc site still says TD3 is it a td or bill?
Tell me about it hahaha.
Ha... ha...
I am darn worried XD
Well 2 models (GFS and ECMWF) that handle shear very well show shear backing off Ana in about 2-3 days. Ironically the GFS still dont develop Ana but explains why the NHC thing some gradual streghtening is possible with Ana.
Wait, a fuigi-wawa affect is happening! Driving Ana more northeast and Bill a bit more southeast? That means Ana could be a fish storm while Bill will cruise the southern Caribbean!
Do we have any models that are picking up on this yet?
Thanks
Something wicked this way comes...
Humberto
Bill is already in the Atlantic.
was that edwourd..?? something like that last year
I notice models are shifting Ana more towards the GOM. Puts me in a predicament because I have plans to head out Monday for a Job near the Gulf coast South of Lafayette. Ahhh, the joys of hurricane season.
That's it - thanks!
from the satellite it looks like it is shear the problem since the llc is expose
That's the one - thanks Storm! Hope you are able to relax a little this weekend!
Humberto unfortunately did develop right before landfall. High Island, TX received sustained winds of 85-90 mph, and an elevated oil platform had gusts well over 100 mph.
Some of the models had been showing a Fujiwhara effect a few days ago, even though the same models weren't really developing either system beyond TD-strength, which I thought was odd.
991. Patrap 3:04 PM CDT on August 15, 2009
The second Tropical Storm of 2009 Forms in less than 24 Hours in the Atlantic Basin
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green ball icon03L.BILL
green ball icon02L.ANA
We've been sleeping since June 1! It's been a long nap
121 knots = 139.244313 mph
:/
It was Humberto, went to bed as a weak TS and woke up a few hours later to a Cat 1.
same here, after it sped it, its location and motion,
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