Hurricane BERTHA

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HURRICANE BERTHA DISCUSSION NUMBER  20
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL022008
1100 PM EDT MON JUL 07 2008

DURING THE AFTERNOON HOURS BETWEEN 1900 AND 2300 UTC...BOTH NHC AND
CIMSS OBJECTIVE T-NUMBERS WERE OSCILLATING AROUND 6.0 ON THE DVORAK
SCALE. NORMALLY THESE NUMBERS CORRESPOND TO AN INTENSITY OF 115
KNOTS.  DURING THAT TIME THE EYE BECAME VERY DISTINCT AND WAS
SURROUNDED BY VERY COLD TOPS.  BERTHA COULD HAVE REACHED A PEAK
INTENSITY A LITTLE BIT HIGHER THAN PREVIOUSLY ESTIMATED DURING THAT
PERIOD. SINCE THEN...OBJECTIVE T-NUMBERS HAVE COME DOWN A LITTLE
BIT AND NEW ESTIMATES SUPPORT AN INTENSITY OF 105 KNOTS.  MINIMUM
CENTRAL PRESSURE HAS ALSO BEEN ADJUSTED. THE INTENSITY IS EXPECTED
TO BE CONTROLLED BY EYEWALL REPLACEMENT CYCLES DURING THE NEXT 12
TO 24 HOURS WHEN BERTHA COULD FLUCTUATE IN INTENSITY. THEREAFTER...
THE OFFICIAL FORECAST CALLS FOR SLIGHT WEAKENING DUE TO INCREASING
SHEAR BUT NOT AS MUCH WEAKENING AS PREDICTED BY THE SHIPS MODEL. 
NEVERTHELESS...THE INTENSITY FORECAST CONTINUES TO BE HIGHLY
UNCERTAIN.

ON THE OTHER HAND...THE TRACK FORECAST HAS BECOME A LITTLE MORE
CERTAIN SINCE THE TRACK MODELS ARE IN BETTER AGREEMENT AND THE
GUIDANCE ENVELOPE IS SMALLER. BERTHA IS MOVING TOWARD THE
WEST-NORTHWEST OR 300 DEGREES AT 10 KNOTS WHILE APPROACHING A
WEAKNESS IN THE SUBTROPICAL RIDGE.  THE RIDGE IS EXPECTED TO
REBUILD SOME AND THIS PATTERN WOULD FAVOR A CONTINUATION OF THE
WEST-NORTHWEST TRACK FOR A DAY OR TWO....FOLLOWED BY A GRADUAL TURN
TO THE NORTHWEST AND NORTH.  BY DAYS 4 AND 5 THE STEERING CURRENTS
ARE FORECAST TO COLLAPSE AND BERTHA WILL PROBABLY MEANDER FOR A
LITTLE BIT.

BERTHA IS CERTAINLY NOT THE ONLY MAJOR HURRICANE THAT HAS FORMED IN
THE MONTH OF JULY. THE LAST OCCURRENCES WERE HURRICANES DENNIS AND
EMILY IN 2005.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      08/0300Z 20.8N  52.8W   105 KT
 12HR VT     08/1200Z 21.5N  54.2W   100 KT
 24HR VT     09/0000Z 22.5N  56.0W   100 KT
 36HR VT     09/1200Z 23.5N  58.0W    95 KT
 48HR VT     10/0000Z 25.0N  59.5W    85 KT
 72HR VT     11/0000Z 27.5N  61.5W    80 KT
 96HR VT     12/0000Z 30.0N  62.0W    75 KT
120HR VT     13/0000Z 32.0N  62.0W    75 KT
 
$$
FORECASTER AVILA
 
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