ZCZC MIATCDAT2 ALL TTAA00 KNHC DDHHMM 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 NNNN
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Page last modified: Tuesday, 21-Apr-2009 12:09:05 UTC