Hurricane Bertha Forecast Discussion #21

By: National Hurricane Center
By: National Hurricane Center

000
WTNT42 KNHC 080832
TCDAT2
HURRICANE BERTHA DISCUSSION NUMBER 21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008
500 AM EDT TUE JUL 08 2008

THE EYE OF THE HURRICANE HAS BECOME A LITTLE LESS DISTINCT OVER THE
PAST SEVERAL HOURS. NONETHELESS...BERTHA HAS BEEN MAINTAINING A
FAIRLY SYMMETRICAL RING OF COLD CLOUD TOPS AROUND THE CENTER.
SUBJECTIVE AND OBJECTIVE DVORAK T-NUMBERS HAVE COME DOWN SLIGHTLY
BUT CURRENT INTENSITY ESTIMATES...BOTH OBJECTIVE AND SUBJECTIVE...
REMAIN CLOSE TO 105 KT. HENCE THE ADVISORY INTENSITY IS UNCHANGED.
SOME FLUCTUATIONS IN STRENGTH ASSOCIATED WITH EYEWALL REPLACEMENTS
COULD OCCUR WITHIN THE NEXT 12 HOURS OR SO. IN THE LONGER-TERM...
THE ENVIRONMENT IS EXPECTED TO GRADUALLY BECOME LESS CONDUCIVE FOR
STRENGTHENING AS BERTHA MOVES TOWARDS HIGHER LATITUDES. THIS IS
REFLECTED IN THE SHIPS MODEL...WHICH WEAKENS BERTHA TO MINIMAL
HURRICANE STRENGTH BY 72 HOURS. THE OFFICIAL INTENSITY FORECAST
CLOSELY FOLLOWS THE INTENSITY MODEL CONSENSUS ICON.

EYE FIXES GIVE A MOTION ESTIMATE OF 310/9 WHICH IS SLIGHTLY TO THE
RIGHT OF PREVIOUS ESTIMATES. GLOBAL MODELS ARE NOW IN FAIRLY GOOD
AGREEMENT THAT BERTHA WILL HEAD FOR A WEAKNESS IN THE
MID-TROPOSPHERIC SUBTROPICAL RIDGE AND TURN NORTHWARD LATER IN THE
FORECAST PERIOD. IT SHOULD BE NOTED THAT THE GFDL AND HWRF MODELS
HAVE BEEN CALLING FOR THIS SCENARIO MORE CONSISTENTLY THAN THE
OTHER GUIDANCE OVER THE PAST COUPLE OF DAYS. THE OFFICIAL TRACK
FORECAST IS ADJUSTED EAST OF THE PREVIOUS ONE BUT IS STILL TO THE
WEST OF MOST OF THE DYNAMICAL MODEL TRACKS AS WELL AS THE MODEL
CONSENSUS. BY DAY 5...STEERING CURRENTS COULD BECOME QUITE WEAK
AND BERTHA MAY MOVE SLOWLY AND ERRATICALLY AS IT WAITS TO BE
EVENTUALLY PICKED UP BY A TROUGH IN THE WESTERLIES.

FORECAST POSITIONS AND MAX WINDS

INITIAL 08/0900Z 21.4N 53.3W 105 KT
12HR VT 08/1800Z 22.2N 54.4W 100 KT
24HR VT 09/0600Z 23.4N 55.9W 95 KT
36HR VT 09/1800Z 24.7N 57.4W 90 KT
48HR VT 10/0600Z 26.0N 58.6W 85 KT
72HR VT 11/0600Z 28.0N 59.5W 80 KT
96HR VT 12/0600Z 30.0N 59.5W 75 KT
120HR VT 13/0600Z 32.0N 59.0W 70 KT

$$
FORECASTER PASCH


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