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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Do I read the GFS and GDL correct, South Fla appears out of the woods?....at the moment for both of these storms?
Ummm...NO!
2nd time youve mentioned homophobia out of that entire rant.?? can we please quit quoting it and move on!
Not at all. There is no such thing as out of the woods if you're in the cone.
best poll ever....
please help me with that I am on the tropical atlantic recon site
Perfect...
Definetly with you on that.
Sorry I just couldn't help it, I see so much bull here this evening the flies are starting to gather on my monitor again.
Excellent...it would be sweet if those moments turn to hours then to days....Gotta love living in the tropics...
that "blob" sure looks uglier by the minute.
Anyway I was wondering...why so many different models with different conclusions? Is one more reliable than another?
then again...
which is why...
The link doesn't work.
http://moe.met.fsu.edu/cgi-bin/gfstc2.cgi?time=2009081512&field=850mb+Vorticity&hour=Animation
Yep, been tracking their positions to see if the two would get close*enough to begin watching for the mutual interaction which would pull TSAna south and TSBill north.
Instead they've gotten 0.37degrees farther apart to nearly 15degrees of separation.
And to cap it off, TSAna has a northerward component in its mostly westward movement, while TSBill has a southward component to its mostly westward movement.
* Less than 13degrees separation
WORD
Time of Latest Image: 20090815 2045 UTC
4km Remapped Color Enhanced Infrared Imagery
Current imagery and loops of 4km remapped and color enhanced infrared (IR) imagery is displayed in an earth fixed coordinate system. IR imagery (~11 um) from five geostationary satellites are remapped to a common 4km resolution Mercator projection in an identical manner as the CIRA Tropical Cyclone Image Archive described in (Mueller et al. (2006) . These images are then centered and displayed using the nearest 5 degree latitude/longitude earth coordinate based on the most recent location and past 12-h movement. The images are also color enhanced with the coldest temperatures/highest clouds displayed as colored shades as shown in this color bar.
ana doesnt have that much mass to begin with
yep those look bad =\
thanks!
At the top of this page click on the link:
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http://www.wunderground.com/tropical/
Under:
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See:
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for a list of Model sites.
We are definitely not out of the woods.
Anyways, the GOM shouldn't worry about Ana. If it were to head that way, it'll definitely die from passing over Cuba, Haiti, or the DR. The only threat this has it to the islands, the Bahamas, and Florida for now.
A hard choice, but I'd say definitely A
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