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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Looks like a Hugo event or a Floyd event.
NHC Tropical Floater
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Remember, they had it in the Caribbean yesterday. To me its to early to talk track, but a lot of the other models still want it to go on the path the NHC is taking.
The other way is "easier", but once you know the format..
But that's still 8 days from now. The models are bound to change....
Definitley some rotation there....
mobilegirl...he or she wants to talk to you privately
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UZNT13 KWBC 152302
XXAA 65222 99190 70533 04293 99015 27228 08017 00129 26023 08020
92814 21631 09528 85545 18021 09522 70187 09650 10525 50590 06520
11013 40761 16958 10004 30971 31975 27504 25097 41970 23017 20245
533// 20524 88999 77999
31313 09608 82220
51515 10190 15424
61616 NOAA9 WX02A ANA OB 06
62626 SPL 1899N05334W 2235 MBL WND 08523 AEV 20801 DLM WND 13510
014152 WL150 08020 082 REL 1897N05330W 222052 SPG 1899N05334W 223
526 =
XXBB 65228 99190 70533 04293 00015 27228 11850 18021 22659 07257
33627 04456 44610 03260 55591 01226 66546 01933 77527 03926 88511
05356 99499 06519 11473 08732 22454 10756 33447 11361 44438 12550
55431 12966 66423 14175 77418 14573 88414 15162 99409 15564 11401
16758 22390 17967 33370 20968 44363 21957 55350 23959 66344 24967
77334 26562 88326 27576 99280 35573 11203 52763 22152 64938
21212 00015 08017 11962 09530 22939 09530 33898 08523 44850 09522
55647 11029 66527 12513 77443 09503 88300 28004 99270 22514 11239
23521 22203 21024 33193 19030 44176 19532
31313 09608 82220
51515 10190 15424
61616 NOAA9 WX02A ANA OB 06
62626 SPL 1899N05334W 2235 MBL WND 08523 AEV 20801 DLM WND 13510
014152 WL150 08020 082 REL 1897N05330W 222052 SPG 1899N05334W 223
526 =
Looking more and more that way. The GFS which really wanted to take Bill into the GOM has been shifting dramatically east all day and now has Bill way east of FL. Local TV met concurs.
I'm not too worried about Ana (at this time). She is such a small storm and if conditions were to go bad ahead of her she can die in hours. Let's give a couple more days and she how she holds together.
We just have to skip Northern California. No sense in going from the "frying pan to the fire!"
Is that really the dynamics it is considering that kills Ana? I wouldn't think Anguilla was enough land to do that. Looks like something else at play there...starts the kill well before land.
Or maybe they just want to be proactive and prepared. I hope no one really wants a storm to hit them...
I wouldn't mind Ana here in PR. As long as she's weak.
If Ana makes it south of the islands then perhaps she'll be able to tap into the moisture taht is so bountiful in the western caribbean. I'm from South Florida, will be here until the 19th, but then i am due to go back to tallahassee. tallahassee does not get much storms.. so i am not too worried. however with the little i know, i do think Ana looks to be a GOM storm, mostly because it has remained weak and may not get picked up by northern pushing steering currents.
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