HURRICANE BERTHA DISCUSSION NUMBER 19

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HURRICANE BERTHA DISCUSSION NUMBER 19
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008
500 PM EDT MON JUL 07 2008

BERTHA'S SATELLITE PRESENTATION HAS CONTINUED TO IMPROVE THIS
AFTERNOON WITH A VERY DISTINCT EYE NOW SURROUNDED BY A RING OF COLD
CLOUD TOPS. SUBJECTIVE DVORAK T NUMBERS WERE UNANIMOUSLY 5.0 BUT
OBJECTIVE NUMBERS HAVE INCREASED TO 6.0 FOR THE PAST 3 HOURS. THIS
SUPPORTS AN INITIAL INTENSITY OF 100 KT MAKING BERTHA A MAJOR
CATEGORY THREE HURRICANE ON THE SAFFIR-SIMPSON HURRICANE SCALE.
BERTHA'S INTENSIFICATION TO MAJOR HURRICANE TODAY HIGHLIGHTS THE
DIFFICULTIES OF FORECASTING RAPID INTENSITY CHANGES. IN THE
SHORT-TERM...SHEAR IS EXPECTED TO BE LOW AND THE INTENSITY WILL BE
PRIMARILY CONTROLLED BY EYEWALL CYCLES. AS A RESULT...SOME
FLUCTUATIONS IN INTENSITY ARE LIKELY. IN A DAY OR TWO...THE GFS
MODEL STILL INDICATES INCREASING SHEAR. THE SHIPS AND LGEM
STATISTICAL MODELS...WHICH BASE THEIR SHEAR ESTIMATES FROM THE
GFS...SHOW WEAKENING BEYOND 24 HOURS AND SO DOES THE OFFICIAL
FORECAST.

BERTHA HAS BEEN MOVING MORE TOWARDS THE NORTHWEST DURING THE LAST
COUPLE OF HOURS WITH A REDUCTION IN FORWARD SPEED...BOTH INDICATIONS
THAT THE HURRICANE HAS REACHED THE MUCH-ANTICIPATED WEAKNESS IN THE
RIDGE. SINCE BERTHA COULD BE WOBBLING...THE INITIAL MOTION
ESTIMATE BASED ON A 12 HOUR AVERAGE IS 300/10. TRACK GUIDANCE
REMAINS IN GOOD AGREEMENT ON A GRADUAL NORTHWARD TURN DURING THE
NEXT 2-3 DAYS. THEREAFTER...GLOBAL MODELS SUGGEST THAT THE
STEERING CURRENTS COULD BECOME WEAK LEADING TO INCREASED UNCERTAINTY
IN THE TRACK FORECAST. EVEN THOUGH THE OFFICIAL FORECAST IS
SHIFTED A LITTLE TO THE EAST...IT IS STILL WAY TOO SOON TO
DETERMINE WHETHER OR NOT BERTHA WILL AFFECT BERMUDA.

FORECAST POSITIONS AND MAX WINDS

INITIAL 07/2100Z 20.1N 52.1W 100 KT
12HR VT 08/0600Z 20.8N 53.5W 100 KT
24HR VT 08/1800Z 21.7N 55.4W 95 KT
36HR VT 09/0600Z 22.9N 57.3W 90 KT
48HR VT 09/1800Z 24.0N 59.0W 85 KT
72HR VT 10/1800Z 26.5N 61.5W 80 KT
96HR VT 11/1800Z 29.0N 62.5W 75 KT
120HR VT 12/1800Z 31.5N 62.5W 75 KT

$$
FORECASTER RHOME


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