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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1164. KEEPEROFTHEGATE (Mod)
Quoting SOUTHFL43YRS:
OMG! I'M EVACING TONIGHT.
just calm down follow guidance from NHC listen to local officials we got a couple days before anything starts to affect people first in line are my friends in northern leewards lets keep things flowing smoothly for them
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It'll be interesting to see if the next run of models keep shifting Ana south.
Member Since: May 17, 2009 Posts: 0 Comments: 559
1162. Patrap
Atlantic Basin 2 Sept 2008



Member Since: July 3, 2005 Posts: 420 Comments: 127536
Quoting sporteguy03:


What type of preparation has your island taken with the two possible threats so close together?


probably the goverment is more concern with Bill, frankly Ana is welcomed rain. But persons have been packing up on supplies and minute little things. School is out and does return until september, so tropical storm watches will only affect those in the business world.

Also, what I have been seeing is that persons are preparing for Bill not Ana and ironically Ana is the 1 to reach 1st.
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TexasHurricane:

I am believing the 12Z UKMET right now...what say you?
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1158. jdjnola
Quoting highndry1:
is it just me or has Ana now covered the COC with enough heavy storms to ride out the shear for the next day or two?


I think her bigger problem is the dry air. Depends on how moisture much Bill gives or takes.
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Yeah I went to bed that night with the local mets calling it an "iffY" TD, and woke up the next morning in a hurricane
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I wonder if Max Mayfield will be working tonight...
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Quoting bballerf50:
I dont see the updated Ana track...may someone please post it? Thanks


Its on this website.

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Looks like it has shifted south a little...

Member Since: July 2, 2009 Posts: 0 Comments: 2811
Quoting WPBHurricane05:
Ana's cone shifted south.


of course it did model cocnsensus is just north of cuba.land interaction might be a big issue with this system as those tall mountains in cuba dont play.
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did anyone found out that now TS ANA is moving faster than TS BILL
ANA
5:00 PM AST Sat Aug 15
Location: 14.4°N 50.0°W
Max sustained: 40 mph
Moving: W at 17 mph
Min pressure: 1005 mb
BILL
5:00 PM AST Sat Aug 15
Location: 11.3°N 35.2°W
Max sustained: 40 mph
Moving: W at 16 mph
Min pressure: 1004 mb
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1151. Relix
It will probably drop south even more. I've been saying it for over 48 hours now... that track was too much far to the north. I just see no way how the center can pass over PR. Now the rain and some wind? Definitely will hit us. Center will probably stay about 100 miles or more south of Ponce.
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I dont see the updated Ana track...may someone please post it? Thanks
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Quoting StormW:
Good afternoon!

Hot off the press!

TROPICAL STORM ANA / TD3 / AUG 15, 2009 SPECIAL UPDATE 3:30 P.M. EDT
Great update StormW. I have a hypothetical, I have often seen local NWS mets use the term "persistence" for forecasting purposes, basically stating they think the trend, or conditon will continue with no cited emperical or scientific basis.

In an anomalous years like this one, is it possible that the "persistence" factor may preclude any modeling data or expected meteorlogical prognostication tools?

Just trying to make sense of low TC year with such high SST's in the Atlantic Basin
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OMG! I'M EVACING TONIGHT.
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1147. 996tt
Quoting WPBHurricane05:


That is if it can survive Hispaniola and Cuba.


he's a fighter. She survived strong shear and a lot of dry air. People counted her out and she's back.
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Bill's intensity is over done...been saying that! it may have been upgraded to TS status but teh East and Northeast side it looks quite poor - Honestly I have seen better looking TDs..
Also, this will go lot more West..I am believing 12z UKMET model which takes in South of PR towards Jamaica...ot thereabouts!

We shall see...what do you guys think?
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Quoting Weather456:
The Dutch government always ahead of ours.


What type of preparation has your island taken with the two possible threats so close together?
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Quoting WPBHurricane05:


That is if it can survive Hispaniola and Cuba.


True, but then it could just skirt them as well.
Member Since: July 2, 2009 Posts: 0 Comments: 2811
Quoting TexasHurricane:


Yes, it has...another one that may need to be watched in the GOM...


That is if it can survive Hispaniola and Cuba.
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Quoting WPBHurricane05:
Ana's cone shifted south.


so has Bill

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What is that near the FL Keys? An open wave?
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Quoting WPBHurricane05:
Ana's cone shifted south.


Yes, it has...another one that may need to be watched in the GOM...
Member Since: July 2, 2009 Posts: 0 Comments: 2811
The Dutch government always ahead of ours.
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Quoting jurakantaino:
Years with the Bermuda high pressure is set up this way is bad news for us in the Leewards . Vieques and the bigger island of PR., for that matter.


That's true Jurakan. Just trying to stay positive, even when right now it looks pretty grim. If it's not Ana then it's Bill or what could end up being Claudette... who knows. :-s
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Venturi garage-space !?!
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1135. 996tt
Ana looks like she is trying to wrap that eye again.
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It looks like Bill is "stealing" moisture from Ana. That's kind of hot, actually. But seriously, I'm sure there's another, more "scientific" explanation for that. BTW, Bill is now on the NHC website (for that one person on here who did NOT know!)
synth
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NHC has confirmed Bill being a Tropical Storm.

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Ana's cone shifted south.
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So here I am on Dominica, Lesser Antilles, waiting to be sideswiped by Ana and maybe hit by Bill-to-be if he keeps going west. Will get high seas on the Atlantic coast of the island in any case, so fihermen are being warned to drag up their boats off the beaches.
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when was the last time two storms were named in the ALT on the same day?

anybody?... I know someone knows this in here...
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is it just me or has Ana now covered the COC with enough heavy storms to ride out the shear for the next day or two?
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..
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SATELLITE IMAGERY INDICATES THAT THE DEPRESSION IN THE FAR EASTERN
ATLANTIC HAS CONTINUED TO BECOME BETTER ORGANIZED. THE CYCLONE IS
LARGE AND HAS NUMEROUS CYCLONICALLY-CURVED CONVECTIVE BANDS WITH
THE OUTFLOW PRIMARILY ON THE WESTERN SEMICIRCLE.

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Quoting alpha992000:


Yup, count me in on those worried. We'll see what happens. I'm prepared for a direct hit from any of those 3 systems just in case. Hopefully we'll be spared once again.
Years in which the Bermuda high pressure is set up this way is bad news for us in the Leewards . Vieques and the bigger island of PR., for that matter.
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TD 3 just became Bill few mins ago. Ana still chugging along...
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1122. jdjnola
Quoting WPBHurricane05:
The 5pm is out.


Hello, Bill.
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1121. Patrap
NEXRAD Radar
Miami, Base Reflectivity 0.50 Degree Elevation Range 248 NMI

Member Since: July 3, 2005 Posts: 420 Comments: 127536
Quoting WPBHurricane05:
Does this affect any WU bloggers??

AT 5 PM AST...2100 UTC...THE GOVERNMENT OF THE NETHERLAND ANTILLES
HAS ISSUED A TROPICAL STORM WATCH FOR 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.


they are in our area
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TROPICAL STORM WATCH ISSUED FOR THE
DUTCH LEEWARD ISLANDS
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1118. txlori
The gulf looks messy! Is the blob south of NOLA that looks to have some spin anything to be concerned about?
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...TROPICAL STORM BILL...THE SECOND TROPICAL STORM OF THE SEASON
FORMS IN THE FAR EASTERN ATLANTIC...

...SUMMARY OF 500 PM AST INFORMATION...
LOCATION...11.3N 35.2W
MAXIMUM SUSTAINED WINDS...40 MPH
PRESENT MOVEMENT...WEST OR 265 DEGREES AT 16 MPH
MINIMUM CENTRAL PRESSURE...1004 MB
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Bill is born!!
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Does this affect any WU bloggers??

AT 5 PM AST...2100 UTC...THE GOVERNMENT OF THE NETHERLAND ANTILLES
HAS ISSUED A TROPICAL STORM WATCH FOR 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.
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Quoting serialteg:
HOUR: 126.0 LONG: -63.10 LAT: 19.80 MIN PRESS (hPa): 920.00 MAX SURF WIND (KNOTS): 121.00

something about being puerto rican and this model forecast doesnt like it :/


Yup, count me in on those worried. We'll see what happens. I'm prepared for a direct hit from any of those 3 systems just in case. Hopefully we'll be spared once again.
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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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