Ana and TD 3 take aim at the Lesser Antilles

By: Dr. Jeff Masters , 16:17:GMT den 15. august 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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what is going on with the trough that suppose to turn these systems north"?
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Quoting tikikopamsxm:
Hi Dan!

we are damned this year!
Good luck to you from Oyster Pond


Pam

One for Monday and one for Thursday or Friday as it stands now,,, what a week!

more worried about TD3 (Bill) which could be a major by the time it hits 63W

We are at sealevel here in Orient

Dan
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Bill looking incredible.
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Quoting Weather456:
they are literally joined together by a line of convergence


They are holding hands
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HWRF and GFDL take Ana to the Gulf.

HWRF thru Cuba and GFDL south of Cuba then NW to the Gulf.
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Quoting Drakoen:
Upper level convergence separates Ana from 03L


Bill better watch that he's not charged with sexual harassment.
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sorry ike, my bad.. they did....a low chance..we will see...
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I just looked at the water vapor loop at http://www.ssd.noaa.gov/goes/east/watl/loop-wv.html and hit the Tropic Forcast Points and it shows that Ana is coming to South Florida. It's still to early to be sure.
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Quoting nola70119:
Watching the Gulf......lot of heat potential in that water.


Oceanic Heat Content in the GOM
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2:00 EDT NHC comments regarding GOM wave

...TROPICAL WAVES...
TROPICAL WAVE IS ALONG 81W/82W S OF 20N MOVING W 15 KT. THIS
WAVE IS ASSOCIATED WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED
ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. RECENT
VISIBLE SATELLITE IMAGERY INDICATES CYCLONIC TURNING ASSOCIATED
WITH LOW LEVEL CLOUDS NEAR THIS WAVE. THE 15/1200 UTC QUIKSCAT
PASS INDICATES WELL-DEFINED CYCLONIC CURVATURE IN THE LOW LEVEL
FLOW NEAR THIS WAVE...WITH E TO SE WINDS OF 15 TO 20 KT WITHIN
120 NM E OF THE WAVE AXIS AND E WINDS AROUND 10 KT WITHIN 120 W
OF THE WAVE AXIS. SCATTERED MODERATE CONVECTION IS WITHIN 90 NM
EITHER SIDE OF THE WAVE AXIS S OF 19N. THIS CONVECTION IS BEING
SUPPORTED BY ATMOSPHERIC INSTABILITY ASSOCIATED WITH AN UPPER
LEVEL LOW CENTERED NEAR 19N84W AND AN UPPER TROUGH EXTENDING
FROM THIS UPPER LOW TO 11N82W.
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Ike, no talk of the blob i see....hope this thing don't catch everyone with there pants down...
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NHC will shift the track further south on Ana. HWRF has it into Cuba and GFDL has it going into the Caribbean.
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397. IKE
Member Since: juni 9, 2005 Posts: 23 Comments: 37858
395. amd
Hmmm, amazing how things can change in a few hours.

Shear seems to be decreasing around Ana and td3, and more west winds are being found near key west (although pressures are still very high, for now).

Also, the upper level low to the south of the wave which was limiting convergence with the keys wave seems to be becoming more broad and weak.

If pressures fall about 4 to 5 mb in the keys in the next few hours, something could be a brewing.

here is the link of the current shear profile in the western Atlantic basin:

Link
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The system in the keys is moving NW.
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Anyone know how to find out if Keesler is going out to look at the blob near the Keys? A C-130 just flew over about 5 minutes ago. I am assuming they are going to look at??
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392. jipmg
wow we are seeing some rapid formation, that thing is blowing up
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If something is really getting started up off the coast of Florida as sat. seems to be suggesting where would the steering currents take it as things look now?
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389. Skyepony (Mod)
Drak~ Thanks for posting nowCOAST that's what I was refrencing. WUndermap has alot going on down there too.
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Quoting mobilegirl81:
Convection is growing over the keys. If it gets any bigger, there will be some thing to worry about.

Thank you and Drak too. I've been watching these buoys for dropping pressure and west shifting winds since 2am. Sorry for my little "outburst" earlier when no-one seemed to notice.
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Hmmmmmmm. Bill looks to be a threat here in NC.....
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386. IKE
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT SAT AUG 15 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
STORM ANA...LOCATED ABOUT 920 MILES EAST OF THE LEEWARD ISLANDS...
AND ON NEWLY-DEVELOPED TROPICAL DEPRESSION THREE...LOCATED ABOUT
740 MILES WEST-SOUTHWEST OF THE CAPE VERDE ISLANDS.

THUNDERSTORM ACTIVITY ASSOCIATED WITH A TROPICAL WAVE HAS BECOME
MORE CONCENTRATED TODAY OVER THE FLORIDA KEYS AND THE ADJACENT
SOUTHEASTERN GULF OF MEXICO. PRESSURES REMAIN HIGH IN THIS AREA...
AND ANY ADDITIONAL DEVELOPMENT...IF ANY...SHOULD BE SLOW TO OCCUR
AS THE SYSTEM MOVES NORTHWESTWARD OVER THE EASTERN GULF OF MEXICO.
THERE IS A LOW CHANCE...LESS THAN 30 PERCENT...OF THIS SYSTEM
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

PUBLIC ADVISORIES ON TROPICAL STORM ANA ARE ISSUED UNDER WMO HEADER
WTNT32 KNHC AND UNDER AWIPS HEADER MIATCPAT2. FORECAST/ADVISORIES
ON TROPICAL STORM ANA ARE ISSUED UNDER WMO HEADER WTNT22 KNHC AND
UNDER AWIPS HEADER MIATCMAT2.

PUBLIC ADVISORIES ON TROPICAL DEPRESSION THREE ARE ISSUED UNDER WMO
HEADER WTNT33 KNHC AND UNDER AWIPS HEADER MIATCPAT3.
FORECAST/ADVISORIES ON TROPICAL DEPRESSION THREE ARE ISSUED UNDER
WMO HEADER WTNT23 KNHC AND UNDER AWIPS HEADER MIATCMAT3.

$$
FORECASTER BEVEN

Member Since: juni 9, 2005 Posts: 23 Comments: 37858
Watching the Gulf......lot of heat potential in that water.
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AOI/XX/XX
MARK
24.4N/81.8W

THREAT AREA #1
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how fast is this area supposed to move away from the keys?
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380. jpsb
Quoting WatchingThisOne:
Anyone watching that blob SW of Florida take a look at the 12Z CMC from 96 to 144 hours.
A few of us have been making noise all morning about that blob, but not much real interest in it yet. I am watching it, it is a lot closer to me then Ana or TD3.
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91L forming near Key west right now,probably our next TD as well as the area drifts NNW,IMO
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Quoting Skyepony:
The trying to develope low down in the FL straits has stepped off Cuba, moving quick, over the keys. A few west winds can be seen there, blowing up quick. Here's from a buoy on the right side. Looks like it's coming up the west side of Fl.

NFB - Northwest Florida Bay, FL (nfbf1)
Local Time: 1:26 PM EDT on August 15, 2009 Location: 25.08 -81.09 |
Buoy Type: Offshore Tower :
Windspeed measured by: obtained from anemometer

Wind direction (W Dir): South (165 - 174 Degrees)
Wind Speed (W Spd): 19.0 kts (21.9 mph)
Wind Gust (W Spd): 23.0 kts (26.5 mph
)
Atmospheric Pressure (AP): 30.02 in
We have a serious problem developing off the keys.
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377. JLPR
Quoting Patrap:
TD 3 Storm Relative 16km Geostationary Water Vapor Imagery

Time of Latest Image: 20090815 1515UTC



Storm Relative 16km Geostationary Water Vapor Imagery

To compliment the 16km storm relative TPW product listed above, water vapor imagery, with a spectral weight near 6.7 um is displayed with the same resolution, projection, and storm relative geometry. Water Vapor imagery is helpful in determining the location of deep convection, indicated by the coldest pixels, relative upper-level moisture content in areas devoid of deep convection, and upper-level atmospheric motions via animation of these images. The imagery can be used to infer favorable and unfavorable regions of environmental forcing (e.g., areas of increased vertical wind shear or atmospheric subsidence).


that wave exiting Africa must be the other storm the GFS wants to develop
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Convection is growing over the keys. If it gets any bigger, there will be some thing to worry about.
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Hi Dan!

we are damned this year!
Good luck to you from Oyster Pond
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Quoting jipmg:
there is a surface low based on wind observation over the everglades, winds coming out of the WEST in key west, and out of the EAST in NAPLES



I can see that. There is evidence that may support a weak area of low pressure
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Quoting cg2916:

Fujiwhara.


They're just a little over the threshold to be considered Fujiwhara. 900 miles, my friend.
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Quoting tropicaltank:
Perhaps explosive development.Near the keys


I agree and see the possibility especially in the GOM.
Member Since: Oktober 21, 2008 Posts: 243 Comments: 3564
370. 996tt
Quoting WatchingThisOne:
Anyone watching that blob SW of Florida take a look at the 12Z CMC from 96 to 144 hours.

12Z CMC

Interesting ...


I think that is Ana you are seeing.
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Quoting Ameister12:

Is it the cluster of thunderstorms hitting the Florida Keys.
Some of us are wondeing what's up at 28N 91W (GOM). Maybe something like a TD or weak TS is what the doctor ordered to take the edge off some of those SST's that are making bath water sound cool. The swirl around KW looks pretty dicey too.
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Ana and Td3 are doing the Fujiwhara effect!

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HWRF making Ana a hurricane still. the run is out thru 42 hours on ncep.
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Oh dear

Quite a week ahead me thinks

Dan (St Martin)
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Something is brewing around Key West, FL. You can see rotation in the convection over the area on visible satellite imagery as well as RGB.
Member Since: Oktober 21, 2008 Posts: 243 Comments: 3564

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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.