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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Quoting flsky:


Go away.


ditto
Member Since: Posts: Comments:
good night all this is my first post thanks for the info and hope when i wake in the mourning 91 is'nt any trouble for us here in LA.
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3062. Patrap
91L Dvorak Image

Member Since: July 3, 2005 Posts: 414 Comments: 125418
3061. 2ifbyC
Radar shows all that activity right off shore and there's nothing here in west Bradenton!
Member Since: Posts: Comments:
Invest #91L (Location: Eastern Gulf Of Mexico)
Lat: 25.9N Lon: 83.1W Moving: NW 18 mph (16 kts) Pressure: 29.91 in (1013 mb)
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Quoting jipmg:


yes you are =P


I checked back and no I'm not!
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Well looks like we got a rain producer in the Gulf. I still cant believe Bill is forecasted to turn so early.
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Any chance in hell of Bill slowing down?
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Quoting stillwaiting:
why in the heck isn't 91L a td a YET???,definately a closed surface low and looking pretty good,I bet its claudette before it comes ashore near destin area,IMO...

Not according to the quikscat.
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Quoting LouisianaWoman:
Ok, so we've been thru this the past, what, week now? We all have *seen* how much the models shift. I want to take a sigh of relief, but it would be premature. I can not tell you how many people miscalculated Katrina. Tons of them kept saying "it's not coming here! ...Those weather men know nothing, they keep switching the path."
Let me be the first to remind you that those same people were stuck on their roofs, in buildings, etc. in 10+ feet of water.
If you want to get that mentality, well, goodluck and god speed.
Amen sister...Amen
Member Since: July 31, 2009 Posts: 0 Comments: 324
3053. jipmg
Quoting CaneWarning:


No I don't.


yes you are =P
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3052. flsky
Quoting WeatherStudent:



Hahahaha, G'evening KMan. I'd take it that you noticed my brand new avatar pic, huh? LOL, you really think so, now why would you say that? I might dress that way, but let me assure you sir, I'm quite the gentlemen.


Go away.
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Here in St Petersburg the wind has been really picking up the last few hours. Totally unscientific I know, but it feels like something is building in the gulf.
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why in the heck isn't 91L a td a YET???,definately a closed surface low and looking pretty good,I bet its claudette before it comes ashore near destin area,IMO...
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DM21...if you get banned for that please know we all appreciate you taking one for ther team...
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Quoting Chicklit:

Is this Invest predicted to move WNW?

One model someone had here showed LA/MS area, another straight up FL coastline. NHC says "THIS SYSTEM SHOULD MOVES TOWARD THE NORTHWEST OVER THE EASTERN GULF OF MEXICO ON SUNDAY."
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3047. Drakoen
Quoting WeatherStudent:
Pat, may you plz post a quick pic of delicious ice cream. Thanks.


LOL! LOL! LOL! @ ur curtains. True Gangster!!!
Member Since: October 28, 2006 Posts: 57 Comments: 29714
0 Z GFS thinks Bill makes a 10 degree turn at 18 UTC today (as in Sunday)
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Quoting Patrap:









NEXRAD Radar
Tampa, Storm Relative Mean Radial Velocity 1.45 Degree Elevation Range 124 NMI


Thanks for that, Patrap.

I have a question...based on the movement of 91L...where do you believe it will eventually end up coming ashore along the gulf coast, whether it develops or not.
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Quoting jipmg:


you keep saying the same thing every 4 minutes


No I don't.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
3042. Grothar
Quoting mtyweatherfan90:


What happens with this map is that they combine both Ana and Bill wind speeds, however you can see two different sections having the one that ends below Bermuda would be Bill's and the one stretching to florida and into the Gulf would be Ana's. Hope it helps. :)
Thank you for the comment, but this image states it is strictly Bill. The projection for Ana is completely different.
Member Since: Posts: Comments:
Ok, so we've been thru this the past, what, week now? We all have *seen* how much the models shift. I want to take a sigh of relief, but it would be premature. I can not tell you how many people miscalculated Katrina. Tons of them kept saying "it's not coming here! ...Those weather men know nothing, they keep switching the path."
Let me be the first to remind you that those same people were stuck on their roofs, in buildings, etc. in 10+ feet of water.
If you want to get that mentality, well, goodluck and god speed.
Member Since: Posts: Comments:
Quoting flsky:

Go away.


ditto
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3037. flsky
Wind and rain in DB shores at the moment, but no big deal. Sorry we can't send some of this to TX.
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3036. Skyepony (Mod)
Quoting jpsb:
Lol, I'll risk it, off topic but why do I have to hit the "show" button to see some posters posts? thanks.


Top right at the top of where the comments start there is a filter. You can set it to see all, the best or inbetween. People get a rating over all by their comments + & - through the years.
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3035. jipmg
Quoting CaneWarning:
If Bill follows the NHC path 5 days out it would be hard for him to hit S. Florida.


you keep saying the same thing every 4 minutes
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3034. Patrap
Hiya nash,looking at 3 storms with 6 tabs open,..and one Marine/Air Channel channel with offshore yakking about the Fray's here,everyone yakking about This and that,storm Fever abounds,..

.."Seem's like we Hit the Mother Load"..

Member Since: July 3, 2005 Posts: 414 Comments: 125418
HUMBERTO! That's the one I've been trying to remember. THANK YOU GBguy.

lol

Yep...pretty good odds, IMHO.
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Link
Is this Invest predicted to move WNW?
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i'm out...too much bickering for me tonight... i will watch all storms until landfall... regardless of where the puters say they are going...
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Quoting kmanislander:


WS, you would look a lot more intimidating if you were not standing in front of the " under the sea " shower curtain.


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3029. GBguy88
Quoting SavannahStorm:


20 years ago this September.


I was one of the few that didn't evacuate Savannah. I remember the day afterward being incredibly eerie. I was very sick with a fever and went to my doctor's office, and he was the only one there, no nurses and I was the only patient. We got lucky with Hugo. I fear the day our luck runs out.


My mom was in south Myrtle Beach during Hugo. Said it was pretty scary.
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Quoting TampaSpin:
Wow i see we have 91L in the GOM now.

Hey Tampa!

Can someone re-post the link in regards to the 91L discussion info. Too many pages to wade through.

Kman - LOL ROFL - the fishies are cute :o)
Member Since: September 3, 2007 Posts: 3 Comments: 1519
Quoting DM21Altestic:
I'm excited for the first time all year. I'm going to be a freshman in high school this year and I wanted to see one nice round of tropical activity before school commences.

I hope you don't see 1 up close and personal.
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If Bill follows the NHC path 5 days out it would be hard for him to hit S. Florida.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
3024. GBguy88
Alright, going out on a limb here, try not to be too rough on me...but what are the odds of 91L doing something Humberto-esque?
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3023. Patrap









NEXRAD Radar
Tampa, Storm Relative Mean Radial Velocity 1.45 Degree Elevation Range 124 NMI
Member Since: July 3, 2005 Posts: 414 Comments: 125418
Quoting KEHCharleston:
I wasn't stuck! I had my hurricane supplies ready in June that year. (And made sure my sisters did too.) Had a succession of wind storm dreams through out the spring of that year. Not psychic, but I do not need to have God hit me on the head too many times before the message comes through.
Seriously, being prepared was a tremendous relief at a very anxiety provoking time.


20 years ago this September.


I was one of the few that didn't evacuate Savannah. I remember the day afterward being incredibly eerie. I was very sick with a fever and went to my doctor's office, and he was the only one there, no nurses and I was the only patient. We got lucky with Hugo. I fear the day our luck runs out.
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Quoting WeatherStudent:
Pat, may you plz post a quick pic of delicious ice cream. Thanks.


WS, you would look a lot more intimidating if you were not standing in front of the " under the sea " shower curtain.
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Quoting BrockBerlin:
lol Ana at 160 knots what the heck is up with the CHIP model, does it assume storms rapidly intensify over mountains?

Obviously not on a track to do that over mountains.
And maybe it is an improvement over SHIPS at 60 hours out. We could use an improvement...our current intensity models are garbage.
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Quoting Grothar:
Link

If Bill is supposed to make a turn. Can anyone explain this from th NHC. The cone is the 11:00 PM advisory. Any please care to comment


What happens with this map is that they combine both Ana and Bill wind speeds, however you can see two different sections having the one that ends below Bermuda would be Bill's and the one stretching to florida and into the Gulf would be Ana's. Hope it helps. :)
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i see the models turn more left with the next run for bill
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I'm off for now. Going to play some guitar. (Not guitar zero. REAL guitar.... :) ) BBL.
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Wow i see we have 91L in the GOM now.
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About JeffMasters

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