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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Ummmm... Hey Guys...

COME LOOK AT THIS:

SHIP @ 6:00z
LOCATION: 27.40N -83.10W
WINDS: 40.0 KTS

Its the first OBS in the link..
National Data Bouy Center
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Pattrap what does that mean?
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Stormchaser I am in Navarre just east of Pensacola. I don't like what I see on that radar. What do you think the chances are that we could be looking at a possible hurricane. Is it just me or are the showers really starting to wrap.
Quoting Stormchaser2007:
Based on radar, surface obs, and buoy obs...

The rapid organization continues.
Quoting Stormchaser2007:
Based on radar, surface obs, and buoy obs...

The rapid organization continues.
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3710. Patrap
Not to sound alarmist,but if you kinda step back,..and look at the 91L Cyclonic vortex,..hopefully its not now becoming a Low within a bigger Low,where as the 91L would be in the Bigger Low,..at the Right front semi-circle


Member Since: July 3, 2005 Posts: 428 Comments: 129833
3709. KEEPEROFTHEGATE (Mod)


TCFA
TRACK CHART
Member Since: July 15, 2006 Posts: 178 Comments: 56021
Quoting MississippiWx:


To be honest, a minimal hurricane is possible (75-85mph). That is only IF it moves that far west, which is possible. Believe it's probably going to move too quickly to strengthen much more than that. However, if it were to move any slower, it would only mean worse news for Gulf Coast residents.


Y'all when we went to bed after the 10 oclock news on september 12,2007 there was no hint that we would wake up to a 90mph hurricane at 2a.m. on September 13. These can bottom out fast. I'm glad Humberto didn't have more time it wouldve been even worse. So this has the potential to get dangerous. Hope not but it can.
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anyone know how long on the blackout?
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Quoting drj27:
anyone think 91L will affect okaloosa county


very good chance!!
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I love this silly discussion of "who called it." Many have been wary of this wave's potential. Patrap's been posting radar for hours, and anyone who took a look at the radar images could see a LLC trying to form. Conditions have been favorable for two days, and the TPC has had a yellow circle on it for that long. We should be reminded to never let our guard down when any wave enters the GOM. I'm gonna go let down the umbrellas around the pool.
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Quoting MississippiWx:


The ridge to the North and East of the system should keep it on a NW path until landfall. Believe the Big Bend is a little too far east for landfall. I'd say MS/AL border to PCB is most likely. Just depends on how much of a dent it can manage to put into the ridge.



On its current path, Apalachicola or points west to Panama City, Florida, would be a good landfall point. It has been moving NNW since starting to develop near Key West and I expect this path to continue. I'm in Tallahassee and expecting quite a rainy day tomorrow from the system.... Local meterologists have increased the rain chance from 50% to 90% today.
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3701. drj27
anyone think 91L will affect okaloosa county
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Quoting FloridaTigers:
How are the new model runs for Ana and Bill looking like?


HWRF edged south, NOGAPS went way south, GFS GFDL stayed the same, never saw the UKMET. 6z statisticals are about to come out.
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3699. Drakoen
nice radar returns
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I hope NHC issues a special advisory on 91L/Claudette. I want to go to sleep but need to update the Panama City paper's Web site if storm watches are posted. Not to hurry them along or anything.
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Humberto was crazy... although this is too..
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Based on radar, surface obs, and buoy obs...

The rapid organization continues.
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How are the new model runs for Ana and Bill looking like?
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Regardless, tropical storm watches will be posted for the Northern gulf coast tomorrow.
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3690. Michfan
Looks like its center is about 75% closed off.
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3689. 789
Quoting stormsurge39:
Stormno did call it!!
yes he did
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Quoting stormsurge39:
Stormno did call it!!

OMG..please
Quoting palmpt:
Stormno called it.
OK..!
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Quoting TexasHurricane:


I heard about the potential through Joe Bastardi on Acuweather (a few days or so back). The wave was not much to look at then. Who knew....I guess Joe did.


Bastardi says every thunderstorm from march through december that's over water is going to form, ten days before it's supposed to happen. He's bound to be right once in a while.
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3686. Patrap
Two distinct feeder bands developing in the right Semi-circle now..

Member Since: July 3, 2005 Posts: 428 Comments: 129833
Quoting Vortex95:


What not Pass Christian Miss?


The Pass in the house.
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Quoting stormsurge39:
MississippiWX, How stong do you think it will be if it hits AL/MS line?


To be honest, a minimal hurricane is possible (75-85mph). That is only IF it moves that far west, which is possible. Believe it's probably going to move too quickly to strengthen much more than that. However, if it were to move any slower, it would only mean worse news for Gulf Coast residents.
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Quoting MississippiWx:
Wow, fairly impressive core with 91L. It might be one of those times that we skip the TD phase and move straight to TS. Gotta get that closed off center confirmation first, though.

Long Rage Tampa Loop


I was just about to say that! Could skip TD status altogether.
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Quoting FloridaTigers:
Surprises like this are why I love weather. I was wrong about this. Futuremet said to watch this wave for days now too


I heard about the potential through Joe Bastardi on Acuweather (a few days or so back). The wave was not much to look at then. Who knew....I guess Joe did.
Member Since: July 2, 2009 Posts: 0 Comments: 2811
MississippiWX, How stong do you think it will be if it hits AL/MS line?
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With the amount of heat content in the GOM...we may be surprised what we find in the Gulf tomorrow. Its currently under an anticyclone and 31C SSTs.

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mornin' folks...it would appear the GOM system is off to a good start. How's that for a "backyard" system? I strongly suspected a short-fuse situation like this was very probable this season.
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Oh, right. Satellite blackout/eclipse. I hate losing data :(
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Surprises like this are why I love weather. I was wrong about this. Futuremet said to watch this wave for days now too
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Wow, fairly impressive core with 91L. It might be one of those times that we skip the TD phase and move straight to TS. Gotta get that closed off center confirmation first, though.

Long Rage Tampa Loop
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3674. drj27
well atleast it want be another opal i hope not anyway
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San Juan NWS office got a little cute in their discussion...XD

TS BILL HAS FORMED IN THE EASTERN ATLC AND IS AT LEAST FIVE DAYS
OF HAVING ANY IMPACT IN THE ISLANDS OF THE NORTHEAST CARIBBEAN.
AS MENTIONED IN THE NHC DISCUSSION THIS SYSTEM IS IN THE DEEP
TROPICS AND EMBEDDED IN THE DEEP EASTERLIES AND THE STORM WILL
HAVE TO MAKE A HARD RIGHT TURN TO MISS THE ISLANDS OF THE LESSER
ANTILLES. NHC FCST HAS BILL PASSING AT 136 NM ASSUMING A PERFECT
FORECAST WHICH ONLY HAPPENS IN A WORLD OF FANTASY.
TRACK ERRORS AT
FIVE DAYS ARE TYPICALLY IN THE ORDER OF 300 NM. GIVEN THE EXPECTED
LARGE SIZE OF THIS STORM WE ALSO NEED TO PAY CLOSE ATTENTION TO
THIS STORM.

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Stormno did call it!!
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For the most up-to-date look at Invest 91L:
Gulf of Mexico
Northern Gulf of Mexico

You get a new GOES image of the storm every 15 minutes, and sometimes more often. I worked hard writing that page for y'all :)
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I wanna see how fast they can scramble Kermit (NOAA 42 - P3 Hurricane Hunter) at McDill AFB...
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3668. Michfan
Holy hell 91L is tightening up fast.
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3667. 789
Quoting btwntx08:
man alot of blogers are gonna get crazy cause theyre gonna say how did this form so quickly and they are be shocked
futuremet has been watching this thing for 7 days now
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3666. palmpt
Stormno called it.
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IT was moving more NNW it looks like its moving more NW now. I think the NHC needs to warn more than just N FL. Gulf Coast.
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Quoting Drakoen:
Satellite blackout sucks... We have the radar though


LOL I agree...I said that on the previous page. It always happens when you need the satellites the most.
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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.

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