Hurricane BERTHA

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HURRICANE BERTHA DISCUSSION NUMBER  33
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL022008
500 AM EDT FRI JUL 11 2008
 
THE LATEST SATELLITE MICROWAVE DATA AT 02Z INDICATED THAT BERTHA WAS
CONTINUING ITS EYEWALL REPLACEMENT CYCLE...WITH A FRAGMENT OF THE
OLD INNER EYEWALL REMAINING INSIDE THE 60 N MI WIDE OUTER EYEWALL. 
INFRARED IMAGERY SINCE THEN SUGGESTS LITTLE CHANGE IN THE STRUCTURE
OF THE HURRICANE.  SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB
REMAIN 77 KT...SO THE INITIAL INTENSITY REMAINS 75 KT.  THE CIRRUS
OUTFLOW IS NOW FAIR TO GOOD IN ALL DIRECTIONS.

THE INITIAL MOTION IS NOW 315/6.  TRACK GUIDANCE IS IN GOOD
AGREEMENT THAT BERTHA WILL TURN NORTHWARD DURING THE NEXT 36 HR AS
A MID-LEVEL RIDGE NORTH OF THE HURRICANE MOVES EASTWARD.  SERIOUS
GUIDANCE DIVERGENCE OCCURS BEYOND THAT TIME.  THE GFS IS NOW
CALLING FOR A SLOW EASTWARD MOTION FROM 48-120 HR...THE UKMET
CALLING FOR A SLOW NORTHWARD MOTION...AND THE ECMWF AND CANADIAN
MODELS TRAPPING BERTHA IN THE SUBTROPICAL RIDGE AND STALLING IT
NEAR 31N61W.  THE OTHER DYNAMICAL GUIDANCE FORECAST BERTHA TO MOVE
SLOWLY NORTH-NORTHEASTWARD IN RESPONSE TO WEAK RIDGING TO THE EAST
AND A SERIES OF MID/UPPER-LEVEL SHORTWAVE TROUGHS MOVING THROUGH
THE EASTERN UNITED STATES.  SINCE THE ECMWF AND GFS ARE NOT SHOWING
MUCH RUN-TO-RUN CONSISTENCY...THE ONLY CHANGE TO THE FORECAST TRACK
FROM THE PREVIOUS ADVISORY WILL BE TO CALL FOR A SLOWER NORTH-
NORTHEASTWARD MOTION AFTER 48 HR.  THE NEW TRACK LIES ON THE LEFT
SIDE OF THE MODEL CONSENSUS IN BEST AGREEMENT WITH THE FLORIDA
STATE SUPERENSEMBLE.

BERTHA IS CURRENTLY UNDER A LARGE UPPER-LEVEL ANTICYCLONE...WITH THE
LARGE-SCALE MODELS FORECASTING THIS TO CONTINUE FOR AT LEAST 36 HR. 
BASED ON A CONSENSUS OF THE INTENSITY GUIDANCE...THE INTENSITY
FORECAST WILL KEEP BERTHA AT 75 KT DURING THIS TIME.  HOWEVER...
THERE IS STILL A CHANCE OF SOME STRENGTHENING AT THE END OF THE
EYEWALL REPLACEMENT CYCLE.  STARTING IN 48-72 HR...IT IS EXPECTED
THAT BERTHA WILL SLOWLY MOVE OUT FROM UNDER THE ANTICYCLONE AND
ENCOUNTER VERTICAL WIND SHEAR.  THIS...COMBINED WITH DECREASING SEA
SURFACE TEMPERATURES ALONG THE FORECAST TRACK...SHOULD CAUSE BERTHA
TO WEAKEN.  OCEAN ANALYSES FROM THE ATLANTIC OCEANOGRAPHIC AND
MARINE LABORATORY SHOW THAT THE WARM WATER UNDER BERTHA IS
RELATIVELY SHALLOW...AND THERE IS A CHANCE THAT THIS SLOW-MOVING
SYSTEM COULD UPWELL COLDER WATER UNDERNEATH IT.  THIS COULD
PARTICULARLY BE A FACTOR IF BERTHA STALLS FOR 24 HR OR MORE.

THE LATEST WIND SPEED PROBABILITIES INDICATE THAT...GIVEN
UNCERTAINTIES IN THE FORECASTS OF BERTHA'S TRACK...INTENSITY...AND
SIZE...THERE REMAINS ROUGHLY A 50% CHANCE THAT WINDS OF TROPICAL
STORM FORCE WILL AFFECT BERMUDA DURING THE NEXT FIVE DAYS.  A
TROPICAL STORM WATCH MAY BE ISSUED FOR THE ISLAND LATER TODAY.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      11/0900Z 28.0N  61.7W    75 KT
 12HR VT     11/1800Z 28.8N  62.3W    75 KT
 24HR VT     12/0600Z 29.7N  62.6W    75 KT
 36HR VT     12/1800Z 30.4N  62.5W    75 KT
 48HR VT     13/0600Z 31.3N  62.0W    70 KT
 72HR VT     14/0600Z 32.5N  61.0W    65 KT
 96HR VT     15/0600Z 34.0N  60.5W    60 KT
120HR VT     16/0600Z 36.0N  59.0W    55 KT
 
$$
FORECASTER BEVEN
 
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