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Tropical Storm Bertha Forecast Discussion #12

By: National Weather Service
By: National Weather Service

000
WTNT42 KNHC 060234
TCDAT2
TROPICAL STORM BERTHA DISCUSSION NUMBER 12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008
1100 PM EDT SAT JUL 05 2008

LATEST SATELLITE IMAGERY INDICATES THAT BERTHA CONTINUES TO EXHIBIT
A CONVECTIVE BURSTING PATTERN WITH THE CENTER CURRENTLY LOCATED
NEAR THE SOUTH SIDE OF THE COLDEST CLOUD TOPS. DVORAK INTENSITY
ESTIMATES ARE UNCHANGED AND SO IS THE INITIAL INTENSITY...45 KT.
BERTHA IS BEGINNING TO ENCOUNTER WARMER WATERS AND THE CYCLONE IS
EXPECTED TO REACH THE 27 DEGREE CELSIUS ISOTHERM IN 36-48 HOURS.
SINCE THE SHEAR IS EXPECTED TO BE LIGHT DURING THIS PERIOD...SLOW
STRENGTHENING IS EXPECTED. THE FORECAST BECOMES MORE UNCERTAIN
BEYOND 48 HOURS DUE TO SPREAD IN THE TRACK MODELS AND THE RESULTING
DIFFERENCES IN THE ATMOSPHERIC CONDITIONS BERTHA MIGHT EXPERIENCE.
A TRACK MORE TOWARDS THE NORTH WOULD ALLOW MORE STRENGTHENING WHILE
A TRACK MORE TOWARDS THE WEST WOULD RESULT IN INCREASING VERTICAL
SHEAR. SINCE THE OFFICIAL TRACK FORECAST TAKES BERTHA INTO AN AREA
WITH MODERATE VERTICAL SHEAR...ARRESTED DEVELOPMENT IS FORECAST
BEYOND 72 HOURS. THIS NEW OFFICIAL FORECAST IS CONSISTENT WITH THE
PREVIOUS FORECAST BUT SLIGHTLY LOWER THAN THE CONSENSUS OF THE
AVAILABLE INTENSITY MODELS.

BERTHA CONTINUES TO MOVE RAPIDLY WESTWARD WITH AN INITIAL MOTION OF
280/18. THIS GENERAL MOTION IS EXPECTED TO CONTINUE FOR THE NEXT
36-48 HOURS COURTESY OF A STRONG RIDGE TO THE NORTH. THEREAFTER...
THE CYCLONE BEGINS TO ENCOUNTER A WEAKNESS IN THE SUBTROPICAL RIDGE
AND TRACK MODELS DIVERGE SIGNIFICANTLY. IN FACT...THE SPREAD IN
THE TRACK MODELS SPAN NEARLY 1300 MILES AT DAY 5 WITH THE UKMET
MODEL KEEPING BERTHA HEADED WESTWARD AND THE HWRF TURNING THE
CYCLONE NORTHWARD. GIVEN THE UNCERTAINTY...THE OFFICIAL FORECAST
IS SIMILAR TO THE PREVIOUS FORECAST AND LIES IN THE MIDDLE OF THE
TRACK MODEL ENVELOPE.

IT SHOULD BE NOTED THAT THERE IS LARGER THAN NORMAL UNCERTAINTY IN
BOTH THE TRACK AND INTENSITY FORECASTS OF BERTHA. ACCORDINGLY...IT
IS MUCH TOO EARLY TO DETERMINE IF BERTHA WILL OR WILL NOT POSE A
THREAT TO ANY LAND AREAS.

FORECAST POSITIONS AND MAX WINDS

INITIAL 06/0300Z 17.0N 41.2W 45 KT
12HR VT 06/1200Z 17.4N 44.0W 45 KT
24HR VT 07/0000Z 18.1N 47.6W 50 KT
36HR VT 07/1200Z 18.9N 51.0W 55 KT
48HR VT 08/0000Z 19.6N 53.7W 60 KT
72HR VT 09/0000Z 21.5N 59.0W 65 KT
96HR VT 10/0000Z 23.5N 63.5W 65 KT
120HR VT 11/0000Z 26.0N 67.5W 65 KT

$$
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