688 
 WTNT42 KNHC 080236
 TCDAT2
 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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