309
WTNT42 KNHC 080301
TCDAT2
TROPICAL STORM FRED DISCUSSION NUMBER 2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072009
1100 PM AST MON SEP 07 2009
A RECENTLY RECEIVED TRMM PASS FROM 2324 UTC SUGGESTS THAT THE CENTER
OF THE CYCLONE IS LOCATED FARTHER SOUTH AND CLOSER TO THE DEEP
CONVECTION. RECENT INFRARED GEOSTATIONARY IMAGERY SHOWS A CURVED
BAND BEGINNING TO WRAP INTO THE LOCATION OF THE SUSPECTED CENTER.
BASED ON THIS EVIDENCE...THE DEPRESSION IS UPGRADED TO TROPICAL
STORM FRED AND THE INITIAL INTENSITY IS SET TO 35 KT. THE SHIPS
MODEL CURRENTLY ANALYZES EASTERLY WIND SHEAR OF ABOUT 15 KNOTS OVER
FRED. THIS SHEAR IS FORECAST TO DECREASE IN ABOUT 12 HOURS...AND
WITH THE CYCLONE MOVING OVER WARM WATER...THIS SHOULD ALLOW FOR
ADDITIONAL STRENGTHENING THROUGH 72 HOURS OR SO. BEYOND THAT
TIME...FRED IS EXPECTED TO ENCOUNTER INCREASINGLY SOUTHWESTERLY
WIND SHEAR AHEAD OF AN UPPER-LEVEL TROUGH. THE COMBINATION OF THE
SHEAR AND COOLER SSTS SHOULD RESULT IN A SLOW WEAKENING AT DAYS 4
AND 5. THE OFFICIAL FORECAST IS ABOVE THE ICON INTENSITY CONSENSUS
FOR THE FIRST 24 HOURS GIVEN THE CURRENT SATELLITE TRENDS...AND IS
CLOSE TO ICON FROM 24 TO 48 HOURS. BEYOND THAT TIME...THE INTENSITY
FORECAST IS CLOSER TO LGEM...SINCE THAT MODEL TYPICALLY HAS A GOOD
HANDLE ON THE EFFECTS OF CHANGING ENVIRONMENTAL CONDITIONS LATE IN
THE FORECAST PERIOD.
THE INITIAL MOTION IS ESTIMATED TO BE 275/13...BUT THIS IS UNCERTAIN
GIVEN THE RECENT RELOCATION OF THE CENTER. THE TRACK GUIDANCE
REMAINS IN GENERAL AGREEMENT ON TAKING THE CYCLONE ON A WESTWARD TO
WEST-NORTHWESTWARD HEADING TO THE SOUTH OF A NARROW SUBTROPICAL
RIDGE AXIS FOR ABOUT 48 HOURS. BEYOND THAT TIME...FRED IS EXPECTED
TO RECURVE INTO A BREAK IN THE RIDGE BETWEEN 30W AND 35W. AT THE
END OF THE PERIOD...MUCH OF THE GUIDANCE SUGGESTS A VERY SLOW
NORTHWARD OR NORTH-NORTHWESTWARD MOTION...AS THE MID-TO UPPER-LEVEL
TROUGH THAT CAUSES THE BREAK IN THE RIDGE LIFTS OUT...ALLOWING WEAK
RIDGING TO BUILD IN NORTH OF FRED. THE OFFICIAL FORECAST TRACK IS
SHIFTED SIGNIFICANTLY TO THE SOUTH OF THE PREVIOUS TRACK DUE TO THE
MORE SOUTHERLY LOCATION OF THE CENTER. BY THE END OF THE
PERIOD...THE OFFICIAL FORECAST SHOWS A TURN TOWARD THE NORTH AND
THE NORTH-NORTHWEST WITH A DECREASE IN FORWARD SPEED...IN GOOD
AGREEMENT WITH THE TVCN MULTI-MODEL CONSENSUS.
FORECAST POSITIONS AND MAX WINDS
INITIAL 08/0300Z 11.8N 26.3W 35 KT
12HR VT 08/1200Z 12.0N 28.0W 45 KT
24HR VT 09/0000Z 12.6N 30.0W 50 KT
36HR VT 09/1200Z 13.6N 31.7W 55 KT
48HR VT 10/0000Z 14.8N 32.9W 60 KT
72HR VT 11/0000Z 17.5N 34.0W 55 KT
96HR VT 12/0000Z 19.0N 34.0W 55 KT
120HR VT 13/0000Z 21.0N 34.5W 50 KT
FORECASTER BRENNAN
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