Ana and TD 3 take aim at the Lesser Antilles

By: Dr. Jeff Masters , 4:17 PM GMT on August 15, 2009

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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

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It appears a half eyewall is forming looking the Tampa, FL radar. Intense convection wrapping around its center and bands are intensifying.
Member Since: October 21, 2008 Posts: 243 Comments: 3564
She's a fighter and don't count her out just yet
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Good morning all. I wake up this morning and I have TD 4 in my backyard. Will this be Claudette. I saw on the TWC that we're under TS warning.
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4461. jdjnola
Quoting homelesswanderer:
Is Ana's speed whats holding her developement in check? 20mph is flying.


After a brief respite yesterday, she's surrounded by dry air... again.
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I see we got TD #4 overnight
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Good morning all

I just took a look at quikscat and can no longer find a closed circulation with Ana. In fact all I see is a wind shift and this tells me that Ana has degraded to an open wave and will likely be declassified later today unless it regenerates once more.

This has not surprised me as I have been saying from yesterday morning it would likely be downgraded or dissipate before reaching the Islands.

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Hello guys, I have lurked around and I come here for all my weather info, I created a blog that I would like you to see, thank you and please leave a comment. I will make another one this morning. The last one was from yesterday
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4456. WxLogic
NAM did a pretty good job handling this weak disturbance... on Friday it was depicting the TW and/or a piece of energy moving up along the FL W coast over the weekend.

Interesting to note... you'll notice that is handling TS ANA in different fashion than other models... since it will be soon within its domain... should be interesting how is depicted @ 12Z.
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Quoting homelesswanderer:
Is Ana's speed whats holding her developement in check? 20mph is flying.


Mostly, yup.

Really having trouble getting convection itself due the centre being embedded into the low level flow. Running away with itself.
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What are the future steering features looking like for Bill? It it going to be a fish or is it supposed to go WNW. The models are pretty consistent on the 5 day but what about thereafter? Thanks
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Is Ana's speed whats holding her developement in check? 20mph is flying.
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4452. ssmate
Quoting jdjnola:


She's been playing that game for the last several days...

I know but that's pretty anemic.
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Quoting WPBHurricane05:


LOL...The little blob at 15N 55W.


Lol. Couldn't see her on that one. But on visible looks like shes trying to make a comeback again. Wrapping convection round her center.
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000
WTNT32 KNHC 161137
TCPAT2
BULLETIN
TROPICAL STORM ANA INTERMEDIATE ADVISORY NUMBER 17A
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022009
800 AM AST SUN AUG 16 2009

...ANA RACING WESTWARD...

A TROPICAL STORM WATCH REMAINS IN EFFECT FOR PUERTO RICO...THE U.S.
VIRGIN ISLANDS...THE BRITISH VIRGIN ISLANDS...MONTSERRAT...
ANTIGUA...BARBUDA...ST. KITTS...NEVIS...ANGUILLA...ST. MAARTEN...
SABA...AND ST. EUSTATIUS. A TROPICAL STORM WATCH MEANS THAT
TROPICAL STORM CONDITIONS ARE POSSIBLE WITHIN THE WATCH AREA...
GENERALLY WITHIN 36 HOURS.

INTERESTS ELSEWHERE IN THE LEEWARD ISLANDS SHOULD MONITOR THE
PROGRESS OF ANA. ADDITIONAL WATCHES AND WARNINGS MAY BE REQUIRED
FOR PORTIONS OF THESE AREAS LATER TODAY.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA IN THE UNITED
STATES...INCLUDING POSSIBLE INLAND WATCHES AND WARNINGS...PLEASE
MONITOR PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE
FORECAST OFFICE. FOR STORM INFORMATION SPECIFIC TO YOUR AREA
OUTSIDE OF THE UNITED STATES...PLEASE MONITOR PRODUCTS ISSUED
BY YOUR NATIONAL METEOROLOGICAL SERVICE.

AT 800 AM AST...1200 UTC...THE CENTER OF TROPICAL STORM ANA WAS
LOCATED NEAR LATITUDE 14.6 NORTH...LONGITUDE 54.7 WEST OR ABOUT 470
MILES...755 KM...EAST-SOUTHEAST OF THE LEEWARD ISLANDS.

ANA IS MOVING TOWARD THE WEST NEAR 20 MPH...32 KM/HR. A TURN TOWARD
THE WEST-NORTHWEST IS EXPECTED WITHIN THE NEXT 24 HOURS. THE
CENTER OF ANA SHOULD REACH THE LEEWARD ISLANDS BY EARLY MONDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 40 MPH...65 KM/HR...WITH HIGHER
GUSTS. LITTLE CHANGE IN STRENGTH IS FORECAST DURING THE NEXT 24
HOURS.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 70 MILES...110 KM
FROM THE CENTER.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 1005 MB...29.68 INCHES.

ANA IS EXPECTED TO PRODUCE RAINFALL AMOUNTS OF 2 TO 4 INCHES OVER
THE LEEWARD ISLANDS...INCLUDING THE U.S. AND BRITISH VIRGIN
ISLANDS...WITH ISOLATED MAXIMUM AMOUNTS OF 6 INCHES OVER
MOUNTAINOUS TERRAIN.

...SUMMARY OF 800 AM AST INFORMATION...
LOCATION...14.6N 54.7W
MAXIMUM SUSTAINED WINDS...40 MPH
PRESENT MOVEMENT...WEST OR 270 DEGREES AT 20 MPH
MINIMUM CENTRAL PRESSURE...1005 MB

THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE CENTER AT
1100 AM AST.

$$
FORECASTER BRENNAN/ROBERTS

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Quoting 10Speed:
TD4 Projected Path

They've got this thing forecast to travel NW. Everything in me says N to NE.


It is moving NNW, and will continue along that general NW to NNW path.. There's wayyy too much high pressure to its east and north for it to move NE, or even NNE, and I don't believe we'll even see a N jog. If it does though, we'll remember you called it.. But it's virtually impossible at this point :/
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Morning all! Realize there's a chance Ana may not make it to the Gulf, but if she does make it there as a weak system, any thoughts on the chances it could then intensify significantly? Trying to stay up on the systems to keep friends/family/etc.. informed. Thanks! :O)
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4447. jdjnola
Quoting ssmate:
Ana not looking that fresh this morning.


She's been playing that game for the last several days...
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WPBHurricane05 "They are the same systems. Invest 91L became TD 4 this morning
stormwatcherCI "It is the same system at different times. 91L became TD4"
IpswichWeatherCenter "Thats Wunderground not being awake."

Thanks for the explanations. That was too weird to deal with before the first cup of coffee.
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Well I believe TD4 will be Claudette in the next 11am EDT advisory. Why? Because it is strengthening rapidly. Latest radar images out of Tampa, FL show intensifying convection around or on the center of the depression. Tremendous bands to the south of the center are wrapping around and these bands will allow for the storm to gather a lot more moisture. Bill will take a while to strengthen quickly given his immense size, but TD4 is another story. It seems the depression has slowed down some allowing it to strengthen quickly. The only think still keeping the depression down is the pressure. That should though as convection continues to wrap into the center. This is a fascinating storm to watch. We can study what 85-90F temperatures, low wind shear of 5-10 knots, an anticyclone and a surface low pressure center would do when combined and this depression is a prime candidate.
Member Since: October 21, 2008 Posts: 243 Comments: 3564
Quoting homelesswanderer:


Ummmm where's Ana?


LOL...The little blob at 15N 55W.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
It's simply crazy to watch how much it has strengthened in just the past 4 hours. Check out this 4-Hour radar loop: (Try increasing the speed of the loop for better effect) 4-Hour Radar Loop

The fact that in just the last hour you can see about 4 or 5 distinct bands of heavy rain forming and you can see the rain intensify around the center of circulation is just scary. IF it keeps up THIS pace of strengthening, well, I wouldn't be surprised to see a very strong TS or, crazy enough, the small possibility of a minimal Hurricane. We shall see, but check out the radar loop for a good look at a strenghtening Claudette.
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NM found her on the visible. :)
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Quoting 10Speed:
TD4 Projected Path

They've got this thing forecast to travel NW. Everything in me says N to NE.

Well, if it does that..at least NE..would be quite a surprize..
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4439. ssmate
I agree, a TD in the gulf a couple of TS's in the ATL, more waves off of Africa, WS's new avatar....It's going to be crazy.
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Quoting ssmate:
Ana not looking that fresh this morning.
Quoting TheDawnAwakening:
If Bill is to become a fish storm, he will have to strengthen rapidly and the trough that is forecast to exit the Eastern CONUS this week will have to strong. However this time of year there is always weaker fronts to move through instead of the stronger fronts we see in fall and Spring. If the trends of the summer continue then the trough will be strong enough to send Bill out to sea. This year has been the year of the trough.


My favorite local met, James Wieland (WPTV - 5), thinks Bill will get sucked up by the trough as well.
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4437. 10Speed
TD4 Projected Path

They've got this thing forecast to travel NW. Everything in me says N to NE.

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Quoting WPBHurricane05:


Yes. It looks like he is moving WNW already. We'll see what the NHC says in a few hours.


Ummmm where's Ana?
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4435. Ossqss
Quoting IpswichWeatherCenter:


Thats Wunderground not being awake.


This place will be nuts when everyone wakes up.

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4434. eddye
bill still can affect fl or north carolina people it is still far out and the models are doing a bad job
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If Bill is to become a fish storm, he will have to strengthen rapidly and the trough that is forecast to exit the Eastern CONUS this week will have to strong. However this time of year there is always weaker fronts to move through instead of the stronger fronts we see in fall and Spring. If the trends of the summer continue then the trough will be strong enough to send Bill out to sea. This year has been the year of the trough.
Member Since: October 21, 2008 Posts: 243 Comments: 3564
4432. ssmate
Ana not looking that fresh this morning.
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NO upgrade for Td4 at 8 AM
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Quoting nishinigami:
Does that mean Bill has stopped moving just south of West?


Yes. It looks like he is moving WNW already. We'll see what the NHC says in a few hours.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
We do not have Claudette yet.

000
WTNT34 KNHC 161139
TCPAT4
BULLETIN
TROPICAL DEPRESSION FOUR INTERMEDIATE ADVISORY NUMBER 1A
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL042009
800 AM EDT SUN AUG 16 2009

...DEPRESSION MOVING NORTH-NORTHWESTWARD...HEADING FOR THE NORTHERN
GULF COAST OF FLORIDA...

A TROPICAL STORM WARNING REMAINS IN EFFECT FROM THE ALABAMA/FLORIDA
BORDER EASTWARD TO THE SUWANNEE RIVER FLORIDA. A TROPICAL STORM
WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE EXPECTED SOMEWHERE
WITHIN THE WARNING AREA WITHIN 24 HOURS.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA PLEASE MONITOR PRODUCTS
ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE FORECAST OFFICE.

AT 800 AM EDT...1200 UTC...THE CENTER OF TROPICAL DEPRESSION FOUR
WAS LOCATED NEAR LATITUDE 28.1 NORTH...LONGITUDE 84.1 WEST OR ABOUT
125 MILES...200 KM...SOUTH-SOUTHEAST OF APALACHICOLA FLORIDA.

THE DEPRESSION IS MOVING TOWARD THE NORTH-NORTHWEST NEAR 16
MPH...AND THIS MOTION IS EXPECTED TO CONTINUE TODAY. ON THE
FORECAST TRACK...THE CENTER OF THE DEPRESSION SHOULD BE VERY NEAR
THE NORTHERN GULF COAST OF FLORIDA BY LATE THIS AFTERNOON.

MAXIMUM SUSTAINED WINDS ARE NEAR 35 MPH...55 KM/HR...WITH HIGHER
GUSTS. STRENGTHENING IS EXPECTED AND THE DEPRESSION IS FORECAST TO
BECOME A TROPICAL STORM PRIOR TO REACHING THE COASTLINE.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 1011 MB...29.85 INCHES.

RAINFALL ACCUMULATIONS OF 3 TO 5 INCHES...WITH ISOLATED MAXIMUM
AMOUNTS OF 10 INCHES ACROSS PORTIONS OF NORTH FLORIDA NEAR THE PATH
OF THE CENTER.

COASTAL STORM SURGE FLOODING OF 3 TO 5 FEET ABOVE NORMAL TIDE
LEVELS CAN BE EXPECTED NEAR AND TO THE EAST OF WHERE THE CENTER
MAKES LANDFALL.

...SUMMARY OF 800 AM EDT INFORMATION...
LOCATION...28.1N 84.1W
MAXIMUM SUSTAINED WINDS...35 MPH
PRESENT MOVEMENT...NORTH-NORTHWEST OR 330 DEGREES AT 16 MPH
MINIMUM CENTRAL PRESSURE...1011 MB

THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE CENTER AT
1100 AM EDT.

$$
FORECASTER BRENNAN/ROBERTS
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4427. WxLogic
Quoting futuremet:


Its small size will only help it even further. It doesn't require as much ambient energy as a mammoth like Bill does. I truly won't be surprised if this become a hurricane.


Indeed...
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Does that mean Bill has stopped moving just south of West?
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Quoting aspectre:
Invest91L at 27.0N,83.5W
TropicalDepressionFour at 27.7N,83.9W
Why two different systems? Traveling at the same speed in the same direction, with less than 55miles/8okilometres from 91L's center to TD4's center.


Thats Wunderground not being awake.
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Quoting aspectre:
Invest91L at 27.0N,83.5W
TropicalDepressionFour at 27.7N,83.9W
Why two different systems? Traveling at the same speed in the same direction, with less than 55miles/8okilometres from 91L's center to TD4's center.
It is the same system at different times. 91L became TD4
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Quoting AirTrafficMan:
Rather amazing that the models for Bill, except UKMET, are in such close agreement over the next 5 days. Not too often you see the spaghetti all lined up. We sensing a fish with this one?


Don't forget Bermuda.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
Advisories out.
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Quoting aspectre:
Invest91L at 27.0N,83.5W
TropicalDepressionFour at 27.7N,83.9W
Why two different systems? Traveling at the same speed in the same direction, with less than 55miles/8okilometres from 91L's center to TD4's center.


They are the same systems. Invest 91L became TD 4 this morning.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
Quoting Cotillion:
TWD has just come out for 805AM, no mention of a Claudette.


It won't - it has to wait for the advisory's to kick in...
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Rather amazing that the models for Bill, except UKMET, are in such close agreement over the next 5 days. Not too often you see the spaghetti all lined up. We sensing a fish with this one?
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Invest91L at 27.0N,83.5W
TropicalDepressionFour at 27.7N,83.9W
Why two different systems? Traveling at the same speed in the same direction, with less than 55miles/88kilometres from 91L's center to TD4's center.
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Quoting nishinigami:
So has Bill started making that WNW turn?


Officially...no, he's still moving west.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
Quoting GeoffreyWPB:
2009 Storms
All Active Year


Atlantic
04L.CLAUDETTE
03L.BILL
02L.ANA



So - 3 named storms in a day and a bit. Based on that we will be on 45 named storms by the end of the month (3 a day for 15 days).
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Wow...in one week we have three named storms.
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ATMOSPHERICS

Sometimes on a late clear night you can pull that station from Denver or Boston out of the dark.

All the elsewheres alter here, as what you remember changes what you think.

Not spider nor plum nor pebble possesses any of the names we give them.

A kite tugging on its string gives you a sense of what%u2019s up there, though it%u2019s translated, and by a string.

Out there, in the dark, the true thing.

by, Susan Hutton
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.