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Tropical Storm ANA


ZCZC MIATCDAT2 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM ANA DISCUSSION NUMBER  13
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL022009
500 AM AST SAT AUG 15 2009
 
SATELLITE IMAGES INDICATE THAT THE TROPICAL DEPRESSION HAS CONTINUED
TO BECOME BETTER ORGANIZED AND IS NOW UPGRADED TO TROPICAL STORM
ANA. THE STORM IS DISPLAYING IMPROVED BANDING IN THE WESTERN
SEMICIRCLE ALONG WITH A BALL OF CONVECTION NEAR THE CENTER. NOAA
BUOY 41041 REPORTED A MINIMUM PRESSURE OF ABOUT 1005 MB AS THE
DEPRESSION PASSED VERY NEAR THE BUOY. THE INITIAL INTENSITY IS
RAISED TO 35 KT FOR THIS ADVISORY IN AGREEMENT WITH DVORAK
INTENSITY ESTIMATES FROM SAB AND TAFB.

THE INITIAL MOTION ESTIMATE IS 270/14. THE GLOBAL MODELS ARE IN
AGREEMENT THAT A DEEP-LAYER RIDGE WILL STRENGTHEN NORTH OF THE
TROPICAL CYCLONE OVER THE NEXT DAY OR SO. THIS PATTERN FAVORS THE
TRACK OF ANA GRADUALLY BENDING FROM A WEST TO A WEST-NORTHWEST
DIRECTION WITH AN INCREASE IN FORWARD SPEED. THE ONLY SIGNIFICANT
OUTLIERS TO THIS TRACK ARE THE GFDL AND GFS...WHICH BOTH WEAKEN THE
SYSTEM RATHER QUICKLY...LEADING TO A MORE WESTWARD TRACK OF THE
CYCLONE. IN A FEW DAYS...SOME OF THE MODELS...SUCH AS THE GFS...
SHOW A WEAKNESS IN THE RIDGE OVER THE WESTERN ATLANTIC THAT COULD
ALLOW THE CYCLONE TO GAIN A LITTLE MORE LATITUDE. THIS WEAKNESS
APPEARS TO BE CAUSED BY THE MID- TO UPPER-LEVEL LOW CURRENTLY NEAR
25N 65W. HOWEVER...THE MAJORITY OF THE GUIDANCE SHOWS THE MID- TO
UPPER-LEVEL LOW MOVING WEST-SOUTHWESTWARD WITH MINIMAL INFLUENCE ON
THE STRENGTH OF THE RIDGE. GENERALLY...THE MODELS THAT HOLD ONTO
ANA ARE IN GOOD AGREEMENT THROUGHOUT THE FORECAST PERIOD. THE NHC
TRACK FORECAST IS SHIFTED TOWARD THE SOUTHWEST FOR THIS ADVISORY...
BUT NOT AS FAR AS THE MODEL CONSENSUS.

THE 0000 UTC GLOBAL MODELS GENERALLY FORECAST A MORE CONDUCIVE
ENVIRONMENT FOR STRENGTHENING THAN PREVIOUS CYCLES...SHOWING A
WEAKER MID-OCEANIC TROUGH AFFECTING THE SYSTEM. IN PARTICULAR...THE
UKMET AND NOGAPS BUILD UPPER-RIDGING NEAR THE CYCLONE WITH LIGHT
SHEAR THROUGH THE PERIOD. HOWEVER...THE ECMWF SHOWS SOME WESTERLY
SHEAR DEVELOPING IN ABOUT A DAY...BUT EVEN THAT MODEL HAS LIGHTER
SHEAR CONDITIONS IN A FEW DAYS. THE INTENSITY GUIDANCE RUNS THE
FULL SPECTRUM THIS MORNING...WITH THE GFDL DISSIPATING THE
SYSTEM...WHILE THE HWRF SHOWS A CATEGORY TWO HURRICANE BY THE END
OF THE FORECAST PERIOD. GIVEN THE UNCERTAINTY IN THE UPPER-LEVEL
ENVIRONMENT LATER IN THE FORECAST PERIOD...THE OFFICIAL INTENSITY
FORECAST IS INCREASED CONSERVATIVELY...IN BEST AGREEMENT WITH THE
SHIPS MODEL BUT BELOW THE INTENSITY CONSENSUS.

A TROPICAL STORM WATCH MAY BE REQUIRED FOR PORTIONS OF THE LEEWARD
ISLANDS LATER TODAY.

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      15/0900Z 14.6N  46.8W    35 KT
 12HR VT     15/1800Z 14.7N  49.4W    40 KT
 24HR VT     16/0600Z 15.3N  52.7W    45 KT
 36HR VT     16/1800Z 16.1N  56.4W    45 KT
 48HR VT     17/0600Z 17.0N  60.0W    50 KT
 72HR VT     18/0600Z 19.5N  67.0W    55 KT
 96HR VT     19/0600Z 22.5N  73.0W    60 KT
120HR VT     20/0600Z 26.0N  78.5W    60 KT
 
$$
FORECASTER BLAKE
 
NNNN


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Page last modified: Thursday, 31-Dec-2009 12:09:03 UTC