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Hurricane BERTHA


ZCZC MIATCDAT2 ALL
TTAA00 KNHC DDHHMM
HURRICANE BERTHA DISCUSSION NUMBER  25
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL022008
500 AM EDT WED JUL 09 2008

THE CLOUD PATTERN ASSOCIATED WITH BERTHA APPEARS TO HAVE BECOME
SLIGHTLY MORE CIRCULAR AND ORGANIZED OVER THE PAST FEW HOURS.  A
SLIGHT EXPANSION OF THE CIRRUS CANOPY OVER THE SOUTHERN AND WESTERN
PORTIONS OF THE CIRCULATION SUGGESTS THAT VERTICAL SHEAR MAY BE
DECREASING.  THIS IS CONSISTENT WITH WATER VAPOR ANIMATIONS WHICH
SHOW AN UPPER-LEVEL CYCLONE NEAR 27N 68W MOVING WESTWARD AND
FARTHER AWAY FROM THE TROPICAL CYCLONE.  DVORAK SATELLITE CURRENT
INTENSITY ESTIMATES ARE ONLY 55 TO 65 KT AND THEREFORE THE CURRENT
WIND SPEED IS ADJUSTED TO 65 KT FOR THIS ADVISORY.  THE SHIPS MODEL
WHICH USES THE GFS UPPER-LEVEL WIND FORECAST DOES NOT SHOW A
DECREASE IN SHEAR OR ANY STRENGTHENING.  HOWEVER THE GFDL AND HWRF
MODELS...BOTH OF WHICH HAVE SOME LIMITED SKILL IN INTENSITY
PREDICTION...FORECAST A MODEST INCREASE IN STRENGTH OVER THE NEXT
48 HOURS OR SO.  MY WIND SPEED FORECAST ONLY HINTS AT THE
POSSIBILITY OF RE-INTENSIFICATION.  HOWEVER BERTHA WILL CONTINUE TO
TRAVERSE WARM WATERS FOR A COUPLE OF DAYS AND SINCE OTHER
ENVIRONMENTAL FACTORS DO NOT APPEAR INHIBITING...IT WOULD NOT BE
SURPRISING TO SEE IT BECOME STRONGER AGAIN.

ALTHOUGH THERE HAS BEEN A FAIR AMOUNT OF SCATTER IN THE CENTER FIXES
OVERNIGHT...MY ESTIMATE OF INITIAL MOTION IS STILL NORTHWESTWARD OR
305/9.  THERE HAS BEEN NO SIGNIFICANT CHANGE IN THE TRACK FORECAST
REASONING FROM THE PREVIOUS ADVISORY PACKAGE.   A MID-TROPOSPHERIC
ANTICYCLONE TO THE NORTH OF BERTHA IS LIKELY TO WEAKEN AS A 500 MB
SHORTWAVE TROUGH MOVES OFF OF THE U.S. EAST COAST IN 2-3 DAYS. 
THIS EVOLUTION SHOULD CAUSE THE MOTION OF THE HURRICANE TO SLOW
FURTHER AND TO TURN MORE NORTHWARD AROUND THAT TIME.  GLOBAL MODELS
INDICATE THAT THE TROUGH WILL MISS BERTHA AND LEAVE IT IN WEAK
STEERING CURRENTS UNTIL NEAR THE END OF THE FORECAST PERIOD WHEN A
NEW AND STRONGER TROUGH APPROACHES THE EAST COAST.  A VERY SLOW
MOTION IS INDICATED AROUND DAYS 3-4 DUE TO THE WEAK STEERING AND
BERTHA COULD ALSO MOVE ERRATICALLY AROUND THAT TIME.  BY DAY 5 THE
OFFICIAL FORECAST SHOWS A SLIGHT INCREASE IN NORTH-NORTHEASTWARD
MOTION IN RESPONSE TO THE SECOND TROUGH.  THE OFFICIAL TRACK
FORECAST IS QUITE CLOSE TO THE VARIABLE DYNAMICAL MODEL
CONSENSUS...TVCN.

IT IS STILL TOO EARLY TO KNOW WHETHER BERTHA WILL HAVE AN IMPACT ON
BERMUDA.  INTERESTS ON THAT ISLAND SHOULD CONTINUE TO MONITOR THE
PROGRESS OF THIS HURRICANE OVER THE NEXT COUPLE OF DAYS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      09/0900Z 23.5N  56.5W    65 KT
 12HR VT     09/1800Z 24.2N  57.8W    65 KT
 24HR VT     10/0600Z 25.4N  59.2W    70 KT
 36HR VT     10/1800Z 26.8N  60.2W    70 KT
 48HR VT     11/0600Z 28.0N  61.0W    70 KT
 72HR VT     12/0600Z 30.0N  61.5W    70 KT
 96HR VT     13/0600Z 31.0N  61.5W    65 KT
120HR VT     14/0600Z 33.0N  61.0W    60 KT
 
$$
FORECASTER PASCH
 
NNNN


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Page last modified: Tuesday, 21-Apr-2009 12:09:05 UTC