102
WTNT42 KNHC 090835
TCDAT2
HURRICANE FRED DISCUSSION NUMBER 7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072009
500 AM AST WED SEP 09 2009
ENHANCED INFRARED SATELLITE IMAGES INDICATE THAT FRED HAS UNDERGONE
RAPID INTENSIFICATION. THE EYE IS NOW EMBEDDED WITHIN CLOUD TOPS
OF -55 DEG C OR COLDER...AND THE DATA T-NUMBER IS AT LEAST 5.0.
THIS CORRESPONDS TO A CONSERVATIVE CURRENT INTENSITY ESTIMATE OF 90
KT. THE UPPER-LEVEL OUTFLOW IS WELL-DEFINED...ESPECIALLY OVER THE
NORTHERN AND WESTERN PORTIONS OF THE CIRCULATION. FRED IS EXPECTED
TO REMAIN IN A LOW-SHEAR ENVIRONMENT FOR THE NEXT 24 HOURS...SO
SOME ADDITIONAL STRENGTHENING IS LIKELY TODAY. IN ABOUT 36 HOURS
OR SO...THE GLOBAL MODELS SHOW THAT THE HURRICANE WILL BE MOVING
INTO INCREASING SOUTH-SOUTHWESTERLY SHEAR ASSOCIATED WITH A LARGE
UPPER-TROPOSPHERIC TROUGH OVER THE CENTRAL ATLANTIC. OVER THE NEXT
FEW DAYS...FRED WILL ALSO BE MOVING OVER SLIGHTLY COOLER SEA
SURFACE TEMPERATURES AND INTO A DRIER MID-LEVEL AIRMASS. THIS
COMBINATION OF ENVIRONMENTAL CHANGES SHOULD BRING ABOUT
WEAKENING...AND OFFICIAL FORECAST SHOWS A WEAKENING TREND
COMMENCING AFTER 24 HOURS. THIS IS FAIRLY CLOSE TO THE LATEST
SHIPS GUIDANCE. THE GFDL AND HWRF MODELS...WHICH SEEM TO BE LESS
SENSITIVE TO INCREASED SHEAR...DO NOT WEAKEN FRED NEARLY AS MUCH AS
THE STATISTICAL/DYNAMICAL GUIDANCE AT DAYS 4 AND 5.
THE MOTION HAS BEEN BENDING GRADUALLY TO THE RIGHT AND IS NOW ABOUT
300/11. THE MID-LEVEL RIDGE TO THE NORTH OF THE HURRICANE HAS BEEN
WEAKENING AS A MID- TO UPPER-LEVEL TROUGH APPROACHES 35W NORTH OF
20N. DURING THE NEXT 72 HOURS...FRED IS FORECAST TO TURN NORTHWARD
INTO THE WEAKNESS CAUSED BY THE TROUGH AND TO DECELERATE AS THE
STEERING FLOW BECOMES VERY WEAK. LATER IN THE PERIOD...THE
DYNAMICAL GUIDANCE SHOWS A WEAK MID-TROPOSPHERIC RIDGE BUILDING TO
THE NORTH AND NORTHEAST OF FRED AND THIS COULD EVENTUALLY BLOCK THE
NORTHWARD MOTION OF THE SYSTEM. THE OFFICIAL FORECAST IS ONLY
SLIGHTLY TO THE WEST OF THE PREVIOUS ONE AND NOT QUITE AS FAST AS
THE MODEL CONSENSUS. THE GFDL AND HWRF TAKE FRED FARTHER NORTH
THAN MOST OF THE OTHER MODELS...PROBABLY BECAUSE THEY KEEP FRED AS
A DEEP CYCLONE FOR TOO LONG.
FORECAST POSITIONS AND MAX WINDS
INITIAL 09/0900Z 13.2N 31.7W 90 KT
12HR VT 09/1800Z 14.1N 32.7W 100 KT
24HR VT 10/0600Z 15.4N 33.9W 100 KT
36HR VT 10/1800Z 16.5N 34.3W 90 KT
48HR VT 11/0600Z 17.3N 34.5W 75 KT
72HR VT 12/0600Z 18.4N 34.2W 60 KT
96HR VT 13/0600Z 20.6N 34.0W 45 KT
120HR VT 14/0600Z 23.0N 34.5W 30 KT
FORECASTER PASCH
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