HURRICANE BERTHA DISCUSSION NUMBER 18

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WTNT42 KNHC 071432
TCDAT2
HURRICANE BERTHA DISCUSSION NUMBER 18
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008
1100 AM EDT MON JUL 07 2008

BERTHA'S SATELLITE PRESENTATION HAS BECOME MORE IMPRESSIVE DURING
THE LAST 6 HOURS WITH A DISTINCT EYE NOW APPARENT. THE INITIAL
INTENSITY IS INCREASED TO 80 KT IN LINE WITH THE CONSENSUS OF THE
VARIOUS SATELLITE ESTIMATES. IN THE SHORT-TERM...THERE ARE NO
APPARENT ENVIRONMENTAL FACTORS WHICH WOULD INHIBIT FURTHER
INTENSIFICATION TODAY AND THE OFFICIAL FORECAST NOW CALLS FOR
BERTHA TO BECOME A CATEGORY TWO HURRICANE. HOWEVER...THE INTENSITY
FORECAST BECOMES MORE UNCERTAIN BEYOND 36 HOURS AS THE GLOBAL
MODELS DISAGREE ON THE DETAILS OF THE DEVELOPMENT OF AN UPPER-LEVEL
TROUGH OVER THE WESTERN ATLANTIC. THE GFS FORECAST THE MOST
UNFAVORABLE ENVIRONMENT WITH BERTHA ESSENTIALLY RUNNING INTO THE
TROUGH. NOT SURPRISINGLY...THE SHIPS AND LGEM STATISTICAL
MODELS...WHICH INCLUDE ATMOSPHERIC INFORMATION FROM THE GFS...SHOW
CONSIDERABLE WEAKENING. MEANWHILE...THE UKMET...GFDL...AND HWRF
MODELS SHOWS A MUCH MORE FAVORABLE ENVIRONMENT AND DELAY WEAKENING
UNTIL THE VERY END OF THE FORECAST PERIOD. THE OFFICIAL INTENSITY
FORECAST LEANS MORE TOWARDS THE HIGHER SHEAR SCENARIO INDICATED BY
THE GFS BUT DOES NOT WEAKEN BERTHA AS FAST AS THE SHIPS AND LGEM
MODELS.

THERE HAS BEEN LITTLE CHANGE IN THE HURRICANE'S HEADING DURING THE
LAST 6 HOURS WITH THE INITIAL MOTION ESTIMATE ESSENTIALLY
UNCHANGED... 285/13. HOWEVER...BERTHA IS BEGINNING TO ENCOUNTER A
WEAKNESS IN THE SUBTROPICAL RIDGE WHICH SHOULD RESULT IN A GRADUAL
TURN TOWARDS THE NORTH AND A REDUCTION IN FORWARD SPEED. THE
MODELS GENERALLY AGREE ON THIS EVOLUTION...BUT THERE REMAINS SOME
SPREAD AMONGST THE MODELS ON WHAT LONGITUDE BERTHA WILL TURN NORTH.
WHILE THE DEGREE OF THE TURN HAS IMPORTANT IMPLICATIONS REGARDING
POTENTIAL IMPACTS TO BERMUDA...IT IS MUCH TO EARLY TO DETERMINE IF
BERTHA WILL ACTUALLY THREATEN THAT ISLAND. HOWEVER...INTERESTS IN
BERMUDA SHOULD MONITOR THE PROGRESS OF THIS SYSTEM. THE NEW
OFFICIAL FORECAST IS NUDGED SLIGHTLY EASTWARD TOWARD THE TRACK
MODEL CONSENSUS.

FORECAST POSITIONS AND MAX WINDS

INITIAL 07/1500Z 19.6N 51.3W 80 KT
12HR VT 08/0000Z 20.3N 53.3W 90 KT
24HR VT 08/1200Z 21.2N 55.5W 90 KT
36HR VT 09/0000Z 22.1N 57.5W 85 KT
48HR VT 09/1200Z 23.2N 59.2W 80 KT
72HR VT 10/1200Z 25.5N 62.0W 75 KT
96HR VT 11/1200Z 28.5N 63.5W 70 KT
120HR VT 12/1200Z 31.0N 63.5W 70 KT


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