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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91L not 90L.
dont need to be much of a met to know that by now
wait... its the other way around! I get it!
ABNT20 KNHC 160542
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
200 AM EDT SUN AUG 16 2009
FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...
THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
STORM ANA...LOCATED ABOUT 710 MILES EAST-SOUTHEAST OF THE LEEWARD
ISLANDS...AND ON TROPICAL STORM BILL...LOCATED ABOUT 905 MILES
WEST-SOUTHWEST OF THE CAPE VERDE ISLANDS.
SATELLITE AND RADAR DATA INDICATE THAT A SMALL AREA OF LOW PRESSURE
IN THE EASTERN GULF OF MEXICO...CENTERED ABOUT 80 MILES SOUTHWEST
OF TAMPA...IS BECOMING BETTER ORGANIZED AND MAY BE DEVELOPING A
CLOSED SURFACE CIRCULATION. ENVIRONMENTAL CONDITIONS ARE FAVORABLE
FOR ADDITIONAL DEVELOPMENT AND THERE IS A HIGH CHANCE...GREATER
THAN 50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE
SOMETIME TODAY. THIS SYSTEM IS EXPECTED TO MOVE NORTHWESTWARD OR
NORTH-NORTHWESTWARD AT ABOUT 15 MPH TODAY. INTERESTS ALONG THE GULF
COAST OF FLORIDA SHOULD CLOSELY MONITOR THE PROGRESS OF THIS
SYSTEM.
ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.
PUBLIC ADVISORIES ON TROPICAL STORM BILL ARE ISSUED UNDER WMO
HEADER WTNT33 KNHC AND UNDER AWIPS HEADER MIATCPAT3.
FORECAST/ADVISORIES ARE ISSUED UNDER WMO HEADER WTNT23 KNHC AND
UNDER AWIPS HEADER MIATCMAT3.
hmmmmm.SW LA - I'm in SE TX about 10-15 min. from LA border.
"MAY BE DEVELOPING A CLOSED SURFACE CIRCULATION"
About when would that be?
It's red now. Just a little delay.
Don't worry the CMC is not a very good model.
I see RED
It's all red now.
is it me or dos that rader show a eye like thing
GOM
POSS WITHIN NEXT 12 HRS OR LESS
Im in New Orleans, what to expect?
SATELLITE AND RADAR DATA INDICATE THAT A SMALL AREA OF LOW PRESSURE
IN THE EASTERN GULF OF MEXICO...CENTERED ABOUT 80 MILES SOUTHWEST
OF TAMPA...IS BECOMING BETTER ORGANIZED AND MAY BE DEVELOPING A
CLOSED SURFACE CIRCULATION. ENVIRONMENTAL CONDITIONS ARE FAVORABLE
FOR ADDITIONAL DEVELOPMENT AND THERE IS A HIGH CHANCE...GREATER
THAN 50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE
SOMETIME TODAY. THIS SYSTEM IS EXPECTED TO MOVE NORTHWESTWARD OR
NORTH-NORTHWESTWARD AT ABOUT 15 MPH TODAY. INTERESTS ALONG THE GULF
COAST OF FLORIDA SHOULD CLOSELY MONITOR THE PROGRESS OF THIS
SYSTEM.
I am laughing at you. And I will be for some time to come. HWRF says 55 mph TS, so it will really be a 40 mph TS. Dangerous? Still not measured to be a closed low.
No, not on board (you just hinted that your office really is that pic I put up a couple of nights ago).
NEXRAD Radar
Tampa, Storm Relative Mean Radial Velocity 0.50 Degree Elevation Range 124 NMI
when did they decide to make a Cat 6???? Isn't Cat 5 open ended??
Like it says, 144 hours after 00 UTC today (Sunday)
I think we will see the pinhole eye by dawn on this one Tazaroo..
this 91L could TD in the AM and strong TS or cat 1 hurricane by noon
the joke is on you.He called it 4 days ago.i saw him when he did it and everyone said HUH?no models showed it and no one took it serious.now look.
And that's why alot of people here have him in our ignore lists
I'm going back to tally by the 18th.
Ana will not survive to make it in the GOM.
https://www.fnmoc.navy.mil/wxmap_cgi/dynamic/NGP/2009081600/ngp10.sfc10m.120.atlantic.gif
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