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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Well if nothing else, maybe 91 will stir up and cool off the hot tub before anybody else gets in.
Member Since: Posts: Comments:
Quoting code1:
Atmo is here? Looking backwards then. Haven't seen that young man since last season.

Hiya, code. Not that much to see for a couple of pages back, really. Some debate on the merits of radar-detected turning and surface obs not necessarily supporting a surface low.
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Swine flu jab link to killer nerve disease: Leaked letter reveals concern of neurologists over 25 deaths in America
Last updated at 11:05 PM on 15th August 2009


Not storm related, but important enough to spread the word.

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Quoting stormsurge39:
What is stearing 91L?

I believe the tail end of a trough.
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Quoting code1:
Sorry atmoaggie, your handle is a play on another blogger. Was thinking it him. We oldies call him atmo. Good info you put out as well though.


atmosweather you mean?
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0z HWRF just came out for Bill...seems to be a slight south shift, hard to tell with no zoom out though...
http://www.coaps.fsu.edu/~maue/extreme/hwrf/bill03l.2009081600/zoom_bill03l.2009081600_anim.html
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Quoting DM21Altestic:
also, do MLC, thelmores, theprogressivemoles, sporteguy03, TerraNova, guygee, Hawkeyewx etc. still post here?


well, I've had many alts over the past since 2006...I'm not about to get into them at the present.


TerraNova and Thel were posting on here today. Not sure about the rest
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Quoting atmoaggie:

They could add to certain situations...like Humberto (I suppose we will never forget that name)

The coverage is limited, you are correct.

Wasn't NOAA or the military dropping new specialized dropsondes last year for data collection? Doesn't the info from them get fed into the GFDL and HWRF models?
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3503. code1
Sorry atmoaggie, your handle is a play on another blogger. Was thinking it him. We oldies call him atmo. Good info you put out as well though.
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I'm going to bed. These storms aren't very exciting.
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http://www.nbc-2.com/Global/category.asp?C=170788
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What is stearing 91L?
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i love the blog at this time of night, during the day it's off the chain,at least most in here during the night and in the early a.m. are civil, keep up the great work guys,i am getting good solid info and observations, in the daytime not so much!!!! ok back to lurking........
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3495. code1
Atmo is here? Looking backwards then. Haven't seen that young man since last season.
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Quoting CatastrophicDL:
Atmo, I thought the WSR-88D was land based radar arrays. Can they reach far enough out to sea to aid in hurricane modeling?

They could add to certain situations...like Humberto (I suppose we will never forget that name)

The coverage is limited, you are correct.
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Quoting DM21Altestic:
This blog still doesn't feel complete to me without jphurricane2006, StormJunkie, lefty and several other of the regs/vets.



i am in contact with jp and he says that it is too early to tell anything about the long range track for bill
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alright im out see you guys on here tomorrow and we can get a better picture of where they go! be nice, nite
Member Since: August 19, 2007 Posts: 0 Comments: 1601
Just an amateur here, but Tampa that link you posted showed a NW direction until the last few frames it looks like it shifted North? Is my untrained eye deceiving me?
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Quoting TampaMishy:
You seem very intelligent when you write on here..I thought you had some type of background in weather.

Let's not get carried away...Um, I mean, thanks.
*aggie doesn't handle compliments well*
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HurricaneKyle why they do flipflop back and forth? It makes no sense to me! I understand they have to project a path at least 72 hours out, but why anymore when its that far out. It drives people nuts who track storms!
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Quoting DM21Altestic:
This blog still doesn't feel complete to me without jphurricane2006, StormJunkie, lefty and several other of the regs/vets.


Stormjunkie is outta town this weekend...he'll be around again Tuesday...
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Just a few:

1999 Hurricane Bret



2007 Hurricane Humberto:



2001 TS Allison:

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Atmo, I thought the WSR-88D was land based radar arrays. Can they reach far enough out to sea to aid in hurricane modeling?
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3485. code1
Quoting DM21Altestic:
This blog still doesn't feel complete to me without jphurricane2006, StormJunkie, lefty and several other of the regs/vets.


If you know of them, who were you before then? Can't work both ways you know.
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Quoting TampaSpin:


I would say its moving NW look at this long loop...



looks like itll have time to develop watch out folks
Member Since: August 22, 2006 Posts: 2 Comments: 1988
Quoting btwntx08:

that can happen too i agree with u



i wouldn't go that far on a dean/emily hit. High is not near that strong however it is a very big possibility that bill could outrun trough and get closer to conus before recurving. I believe models are recurving it way to quickly. If I remember yesterday afternoon all models except for one had it going towards florida
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Quoting iluvjess:
Pat and Orca. Challenge Question. How many named tropical systems have ever been born and reached atleast TS status while never leaving the shelf? Could 91L be the first ever if it reaches storm status?


Many, many storms have done that. Major hurricanes, in fact, have done that. Not uncommon at all.
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3478. code1
Quoting Twinkster:
I am not a troll and never have been a troll. I used to post my own blog on this website regularly but i don't post much here any more because of all the bickering.

Before i go out for the night i don't see trough being so strong and ridge weakening as much as forecast by models so florida might be out of the question but the carolinas northward could still have a problem, not saying a florida landfall is not possible


We're all in FL, and the Gulf States are wishing the same here. Time for a NE hit. Let the gulf coasts rest a bit!!
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Quoting atmoaggie:

Buoys are quite capable of measuring 84 mph winds in 56 foot waves. I know most of the moored ones have a 50-foot tether.





And I want to fess up. I have been holding out on you. I am a met. My job is to build hurricane wind fields based on all available observations for the sake of storm surge modeling. I, and my office, have done this for about 8 years and have done so for USACE, NASA, NOAA, coastal engineers, forensic studies.
We use a fair bit of analysis when there are no surface obs and I agree that the radar is showing some nice mid-level turning...but that does not always mean surface low. Maybe it is and maybe it is not there right now, but will be soon. Still a possibility it doesn't do much, if any, development.

Hey, anyone know what models was supposed to get assimilation of the WSR-88D data? Was that starting this year?
You seem very intelligent when you write on here..I thought you had some type of background in weather.
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every Claudette in the gulf of mexico has hit TEXAS
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Quoting Tazmanian:



i see your looking for a 24hr ban???


some one was posting photos a fish and they got ban last year for 24hrs so if i where you i would re move it


thanks for the warning. actually even stormW puts up pictures like this in a fun manner. so he would also be at risk? i assume... not?
Member Since: August 22, 2006 Posts: 2 Comments: 1988
Quoting iluvjess:
Pat and Orca. Challenge Question. How many named tropical systems have ever been born and reached atleast TS status while never leaving the shelf? Could 91L be the first ever if it reaches storm status?

It loses based on Humberto alone. I am sure there are more, too.
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Quoting TampaMishy:
Not much of a summer when the weather is like that.

As long as it is short lived it's nice. We did have to skip the HUGE 200 year family reunion today though due to the rain and mud.

Let us all know when you have a shift in your winds there!
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am out of here at 10:30pm


sunday mode runs may have it runing in too FL
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Quoting stormsurge39:
Whats got most models shifting N on Bill?


They believe that 120 hours the trough will be in place to curve Bill out to sea. But they had it earlier as the ridge holding in place and Bill pretty much slams Florida. So they will flip flop back and forth the next couple of days before we really find out whats going to happen. All depends on the trough, it could stall out or Bill might relocate its COC.
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Quoting stormsurge39:
Tampa spin does 91L look like its going more N?


I would say its moving NW look at this long loop...

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See Tampa I did not know that! Here we look for hook echos thats what causes our grief!
Member Since: August 19, 2007 Posts: 0 Comments: 1601
3467. Patrap
Quoting iluvjess:
Pat and Orca. Challenge Question. How many named tropical systems have ever been born and reached atleast TS status while never leaving the shelf? Could 91L be the first ever if it reaches storm status?





Can I wait till we get a Red Light..?,I Like da red Lite Challenge the best...
Member Since: July 3, 2005 Posts: 428 Comments: 129767
Quoting HaboobsRsweet:

Well usually what happens is the shape of NC and the Outer Banks puts that in harms way first before it could reach the mouth of the Chesapeake or eastern VA. I guess it could happen but the Outer Banks would take a beating first.


Yeah...like in Georgia, the angle of the coast makes it rare for a hurricane to hit there.
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Quoting DM21Altestic:
I believe it was Drak himself that got banned for fishcasting last year during Hurricane Bertha. He correctly predicted that Bertha was going to be a fish storm, and to express that, he posted a fish.


Bertha effected Bremuda. Bertha wasn't a fish.
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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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