Ana and TD 3 take aim at the Lesser Antilles

By: Dr. Jeff Masters , 04:17 PM GMT on Αύγουστος 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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I can't believe TS Bill still has 40mph!
Member Since: Αύγουστος 9, 2009 Posts: 10 Comments: 4504
Apparently the NHC is waiting a bit more to up the winds, still at 40 mph. at 11 p.m.
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2761. nash28
Good lord. I thought this "Drak is a freshman" crap was over by now.

This is one of the copious amounts of reasons why I hesitate to blog in here anymore.
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Quoting Skylink:


Where is that???


Jamaica
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2759. 996tt
Quoting lopaka001:
I still see shear tearing at Ana, but she sure is resilient..
Maybe it is my eyes, but the latest image shows the COC way in front of the convection to her west..




You are correct about COC.
Member Since: Σεπτέμβριος 5, 2008 Posts: 0 Comments: 308
...SUMMARY OF 1100 PM AST INFORMATION...
LOCATION...11.3N 36.6W
MAXIMUM SUSTAINED WINDS...40 MPH
PRESENT MOVEMENT...WEST OR 270 DEGREES AT 16 MPH
MINIMUM CENTRAL PRESSURE...1004 MB
Member Since: Ιούλιος 24, 2005 Posts: 407 Comments: 19076
91L should be monitored very close. The overall pattern and given the speed of growth and the SST's.
Member Since: Σεπτέμβριος 22, 2005 Posts: 11 Comments: 2032
ZCZC MIATCPAT3 ALL
TTAA00 KNHC DDHHMM
BULLETIN
TROPICAL STORM BILL ADVISORY NUMBER 3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009
1100 PM AST SAT AUG 15 2009

...BILL MOVING WESTWARD OVER THE FAR EASTERN ATLANTIC...

AT 1100 PM AST...0300 UTC...THE CENTER OF TROPICAL STORM BILL WAS
LOCATED NEAR LATITUDE 11.3 NORTH...LONGITUDE 36.6 WEST OR ABOUT 905
MILES...1460 KM...WEST-SOUTHWEST OF THE CAPE VERDE ISLANDS.

BILL IS MOVING TOWARD THE WEST NEAR 16 MPH...26 KM/HR...AND THIS
MOTION WITH A GRADUAL TURN TO THE WEST-NORTHWEST IS EXPECTED DURING
THE NEXT 24 TO 48 HOURS.

MAXIMUM SUSTAINED WINDS ARE NEAR 40 MPH...65 KM/HR...WITH HIGHER
GUSTS. SOME STRENGTHENING IS FORECAST AND BILL IS FORECAST TO
BECOME A HURRICANE DURING THE NEXT FEW DAYS.

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

ESTIMATED MINIMUM CENTRAL PRESSURE IS 1004 MB...29.65 INCHES.

...SUMMARY OF 1100 PM AST INFORMATION...
LOCATION...11.3N 36.6W
MAXIMUM SUSTAINED WINDS...40 MPH
PRESENT MOVEMENT...WEST OR 270 DEGREES AT 16 MPH
MINIMUM CENTRAL PRESSURE...1004 MB

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

$$
FORECASTER AVILA

NNNN

Bill:
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..
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Must resist the power of F5!
Member Since: Αύγουστος 9, 2009 Posts: 10 Comments: 4504
Interesting if 91L tightens up and slows down.
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After looking at RGB imagery for 91L, it appears convection is developing over the area of the surface low if there is one right now. Convection is developing and rotating with the disturbance, so this has a good chance at developing into a tropical cyclone.

Convection is starting to expand northwestward with Bill. He could be a 50mph storm at 11pm.
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2749. Skylink
Quoting weatherwatcher12:

Here we are under 30%


Where is that???
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000
WTNT32 KNHC 160246
TCPAT2
BULLETIN
TROPICAL STORM ANA ADVISORY NUMBER 16
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022009
1100 PM AST SAT AUG 15 2009

...ANA STILL RACING WESTWARD WITH NO SIGNS OF STRENGTHENING...

AT 11 PM AST...0300 UTC...THE GOVERNMENT OF THE BRITISH VIRGIN
ISLANDS HAS ISSUED A TROPICAL STORM WATCH FOR THE BRITISH VIRGIN
ISLANDS WHICH INCLUDES MONTSERRAT... ANTIGUA...BARBUDA...
ST.KITTS...NEVIS AND ANGUILLA. AT 11 PM AST...0300 UTC...A
TROPICAL STORM WATCH HAS BEEN ISSUED FOR THE U.S. VIRGIN ISLANDS. A
TROPICAL STORM WATCH REMAINS IN EFFECT 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.

INTERESTS ELSEWHERE IN THE LEEWARD ISLANDS...AND PUERTO RICO SHOULD
MONITOR THE PROGRESS OF ANA. ADDITIONAL WATCHES AND WARNINGS MAY BE
REQUIRED FOR PORTIONS OF THESE AREAS TONIGHT AND SUNDAY.

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 1100 PM AST...0300 UTC...THE CENTER OF TROPICAL STORM ANA WAS
LOCATED NEAR LATITUDE 14.4 NORTH...LONGITUDE 51.5 WEST OR ABOUT 710
MILES...1140 KM...EAST-SOUTHEAST OF THE LEEWARD ISLANDS.

ANA IS MOVING TOWARD THE WEST NEAR 17 MPH...28 KM/HR. A GRADUAL TURN
TO THE WEST-NORTHWEST AND AN INCREASE IN FORWARD SPEED IS EXPECTED
DURING THE NEXT TWO DAYS. ON THIS TRACK...THE CENTER OF ANA WILL BE
MOVING OVER THE LEEWARD ISLANDS ON 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 1004 MB...29.65 INCHES.

...SUMMARY OF 1100 PM AST INFORMATION...
LOCATION...14.4N 51.5W
MAXIMUM SUSTAINED WINDS...40 MPH
PRESENT MOVEMENT...WEST OR 270 DEGREES AT 17 MPH
MINIMUM CENTRAL PRESSURE...1004 MB

AN INTERMEDIATE ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE
CENTER AT 200 AM AST FOLLOWED BY THE NEXT COMPLETE ADVISORY AT 500
AM AST.

$$
FORECASTER AVILA

2747. jipmg
Quoting lopaka001:
I still see shear tearing at Ana, but she sure is resilient..
Maybe it is my eyes, but the latest image shows the COC way in front of the convection to her west..




no its not your eyes, that little swirl of clouds you see there is ana's center.
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In response to a recent infection from a "special" weather advisory, 91L has lost all semblance of lower level convergence.

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2745. IKE
Quoting lopaka001:
I still see shear tearing at Ana, but she sure is resilient..
Maybe it is my eyes, but the latest image shows the COC way in front of the convection to her west..




System looks pathetic.
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2744. sfla82
Quoting stormhank:
as of now...does it seem the east coast will be spared any affects from bill?? I noticed models r trending to curve it north around 70-75W longitude??


Yeah we are spared. Bill looks to be a monster storm, but the good thing is most of can just watch him go out to sea with no worries!!!!
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Member Since: Ιούλιος 24, 2005 Posts: 407 Comments: 19076
I still see shear tearing at Ana, but she sure is resilient..
Maybe it is my eyes, but the latest image shows the COC way in front of the convection to her west..



Enlarge Image click here!
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What a day....from nada to (2,0,0)
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2737. jipmg
Wow.. Bill is erupting 0-0
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Quoting weatherboykris:
Bill is going right along the NHC forecast points right now. It is not going in the direction the models would indicate, though. I expect little change at 11.




has of right now all mode run most be thorn in the trash and we start all there worth less right now thorn them out the window
Member Since: Μάιος 21, 2006 Posts: 5089 Comments: 114071
NEW ENTRY POSTED:
South Florida StormWatch
Member Since: Posts: Comments:
Quoting AllStar17:


No....no.....no.....no....no

El Nino will certainly not last a couple of years, and some signs show it has already peaked, and is weakening.


ENSO chart shows it back to warm neutral conditions by February 2010. Looks likely a neutral with a possible cool bias for the 2010 season, like 2008.
Member Since: Αύγουστος 10, 2009 Posts: 3 Comments: 672
Quoting bluewaterblues:
It is amazing the damage that hurricanes can well inland...

You are so right, I am guilty of thinking in the limited terms of "point of impact" and coastal damage. More people are affected then we realize sometimes.
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Quoting TheDawnAwakening:
Taz, I agree. 91L is much closer to home and is much more important right now. We could have a possible Humberto of 2007 situation. Also to remember that a rapidly intensifying storm is likely to slow down some more.

There are watches for the leewards for Ana. So for now I'll keep my eye on Ana
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2731. KEEPEROFTHEGATE (Mod)
AOI/91L/XX
MARK
26.1N/83.5W
Member Since: Ιούλιος 15, 2006 Posts: 165 Comments: 52343
Member Since: Ιούλιος 24, 2005 Posts: 407 Comments: 19076
Bill is going right along the NHC forecast points right now. It is not going in the direction the models would indicate, though. I expect little change at 11.
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91 looks to be coming together...
Member Since: Αύγουστος 14, 2007 Posts: 0 Comments: 435
2727. GatorWX
Quoting washingaway:


I love you man


I love when people try so hard! How could that possibly be for real. you could have studied english for 3 weeks and write better than that! I simply don't understand?????
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Still no advisories
Quoting jipmg:


so bill has the potential to move out of the cone of uncertainty then, since its continuing on a due west movement


No one has any idea about how the ridges will affect Ana, let alone Bill another few days out. Way too many variables out there...
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2724. viman
Quoting Weather456:


its Ana and shes currently moving at a pretty fast clip so Monday night seems reasonable.


What about fluctuations in intensity, I noticed that most of the pm that the center was exposed, you think we can get more than what we're expecting?
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I think Bill might be at 50 mph. by 11 p.m. which is in minutes from now.
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Quoting AllStar17:


There is not an 11 pm TWO, it is a 2 am TWO


"Special outlooks may be issued as conditions warrant."
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2720. Drakoen
Run the water vapor imagery and you can see a push of dry air on Bills northwestern side prevent the system from wrapping around in the mid to upper levels. The zone of upper level convergence is not helping Bill.
Member Since: Οκτώβριος 28, 2006 Posts: 57 Comments: 29714
Quoting Ameister12:
It looks like Ana might be completely exposed again.




Continuing her waxing and waning trend, but do not write her off.
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2718. Relix
Quoting reedzone:


Bill is intensifying and is a possible threat down the road.


And it's a threat to me. I am worried focus will shift too much to 91L and people forget we at the antilles will get hammered =(. I don't think we in PR wll receive a direct impact but it won't do bad to check.
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Quoting Skylink:


no doubt about it, we need the rain so bad, lakes are less than 50% full, and they just closed the last boat ramp on Lake Travis, I think we will need 3 tropical systems here to end the drought. But there's always hope.

Here we are under 30%
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Quoting DestinJeff:
Link

looks like 91L is right along 84W, just N or 26N. some deep convection to the north, but doesn't look to be wrapping just yet. note the nice semi-circle created by the circulation on the southern side.

lots of hot water now, land interaction a non-factor. current vector goes to central gulf coast, but would expect some deviation from straight-line path (right of straight)

Land interaction is a big factor, the florida peninsula is right there.
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It looks like Ana might be completely exposed again.


Member Since: Αύγουστος 9, 2009 Posts: 10 Comments: 4504

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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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