Tropical Storm BERTHA

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TROPICAL STORM BERTHA DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL022008
1100 PM EDT THU JUL 03 2008
 
BERTHA'S SATELLITE PRESENTATION HAS IMPROVED DURING THE LAST 6 HOURS
COURTESY OF A NEW BURST OF DEEP CONVECTION THAT BEGAN AROUND 1900
UTC.  BANDING FEATURES ARE ALSO BECOMING MORE PROMINENT IN BOTH
CONVENTIONAL AND MICROWAVE SATELLITE IMAGERY.  BASED ON THIS
TREND...THE INITIAL INTENSITY IS RAISED TO 40 KT WHICH IS A
COMPROMISE BETWEEN DVORAK INTENSITY ESTIMATES OF 45 KT AND 35 KT
FROM TAFB AND SAB...RESPECTIVELY.  DURING THE NEXT COUPLE OF
DAYS...BERTHA IS FORECAST TO BE LOCATED WITHIN A FAVORABLE
ATMOSPHERIC ENVIRONMENT BUT OVER MARGINALLY WARM SSTS.  SUCH
CONDITIONS SHOULD ALLOW FOR SLOW STRENGTHENING IN THE SHORT-TERM. 
THE OFFICIAL INTENSITY FORECAST IS ESSENTIALLY AN UPDATE OF THE
PREVIOUS ONE AND KEEPS BERTHA JUST BELOW HURRICANE STRENGTH OUT OF
RESPECT OF THE HWRF MODEL.  BEYOND 72 HOURS...VERTICAL SHEAR IS
FORECAST TO INCREASE AND THIS IS REFLECTED IN THE OFFICIAL FORECAST
WITH ARRESTED DEVELOPMENT.

A SERIES OF VERY USEFUL MICROWAVE PASSES INDICATES THAT BERTHA IS A
LITTLE FARTHER SOUTH THAN PREVIOUSLY THOUGHT WITH AN INITIAL MOTION
MORE TOWARDS THE WEST...280/12.  IT WOULD APPEAR THAT THE RECENT
BURST OF CONVECTION IS CAUSING THE CYCLONE TO RESPOND TO THE LARGE
MIDDLE TO UPPER-LEVEL RIDGE TO ITS NORTH.  THIS RIDGE SHOULD KEEP
BERTHA ON A GENERAL WEST-NORTHWESTWARD HEADING OVER THE NEXT 2-3
DAYS.  THEREAFTER...MOST OF THE DYNAMICAL MODELS INDICATE A TURN
TOWARDS THE NORTHWEST AS BERTHA REACHES A BREAK IN THE RIDGE.  EVEN
THOUGH BOTH THE UKMET AND ECMWF SHOW A SIMILAR EVOLUTION IN THE
LARGE-SCALE PATTERN...THESE MODELS KEEP A WEAKER AND SHALLOWER
CYCLONE ON A WEST-NORTHWESTWARD MOTION THROUGH THE ENTIRE FORECAST. 
SINCE THE OFFICIAL FORECAST ASSUMES BERTHA WILL REMAIN A DEEP
SYSTEM...A TURN TOWARDS THE NORTHWEST IS INDICATED BEYOND 72 HOURS. 
THIS IS SIMILAR TO THE PREVIOUS FORECAST...ALBEIT A BIT FARTHER
SOUTH TO ACCOUNT FOR THE INITIAL POSITION RELOCATION. 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      04/0300Z 13.4N  27.0W    40 KT
 12HR VT     04/1200Z 13.8N  29.2W    45 KT
 24HR VT     05/0000Z 14.6N  32.5W    45 KT
 36HR VT     05/1200Z 15.5N  35.9W    50 KT
 48HR VT     06/0000Z 16.6N  39.4W    55 KT
 72HR VT     07/0000Z 18.5N  45.5W    60 KT
 96HR VT     08/0000Z 21.5N  51.0W    60 KT
120HR VT     09/0000Z 25.5N  54.0W    60 KT
 
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FORECASTER RHOME
 
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