Tropical Storm NORBERT

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TROPICAL STORM NORBERT DISCUSSION NUMBER   9
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP152008
800 PM PDT SUN OCT 05 2008
 
DEEP CONVECTION HAS BEEN WAXING AND WANING AROUND THE LOW-LEVEL
CIRCULATION CENTER THIS AFTERNOON AND EVENING...BUT THE OVERALL
TREND HAS BEEN FOR IMPROVED ORGANIZATION. DVORAK SATELLITE
INTENSITY ESTIMATES ARE T3.0/45 KT FROM BOTH TAFB AND SAB.
HOWEVER...3-HR AVERAGE ODT/ADT ESTIMATES HAVE BEEN T3.8 TO T3.9. 
ALSO...THERE WAS A 05/2317Z AMSU INTENSITY ESTIMATE OF 55 KT.
THEREFORE...THE INITIAL INTENSITY HAS BEEN INCREASED TO 55 KT.

THE INITIAL MOTION ESTIMATE IS 270/07. THE INITIAL POSITION WAS
ADJUSTED SLIGHTLY TO THE SOUTH OR LEFT OF THE PREVIOUS TRACK BASED
ON A 05/2022Z AMSR OVERPASS...WHICH REVEALED A TIGHT LOW-LEVEL
CIRCULATION CENTER IN THE 37 GHZ CHANNEL ALONG 14N LATITUDE. OTHER
THAN THE SLIGHT SOUTHWARD RELOCATION...THERE IS NO SIGNIFICANT
CHANGE TO THE PREVIOUS FORECAST TRACK OR PHILOSOPHY. FOR THE NEXT
96 HOURS...NORBERT IS EXPECTED TO GRADUALLY MOVE WEST-NORTHWESTWARD
AND THEN TURN NORTHWESTWARD AROUND THE WESTERN PERIPHERY OF A
SUBTROPICAL RIDGE SITUATED TO THE NORTH OF THE CYCLONE. AFTER
THAT...A MID-LEVEL SHORTWAVE TROUGH IS FORECAST TO DROP SOUTHWARD
ALONG THE U.S. WEST COAST AND INTO THE U.S. DESERT SOUTHWEST BY 120
HOURS...WHICH SHOULD WEAKEN THE RIDGE AND ALLOW NORBERT TO TURN
MORE TOWARD THE NORTH. THE OFFICIAL FORECAST TRACK IS SIMILAR TO
THE PREVIOUS ADVISORY AND IS ALSO SIMILAR TO BUT FASTER THAN THE
NHC MODEL CONSENSUS...TVCN.
 
THE MODERATE EASTERLY SHEAR THAT HAS BEEN PLAGUING NORBERT FOR MANY
DAYS NOW IS EXPECTED TO DECREASE SLIGHTLY AND SHIFT AROUND FROM THE
SOUTHEAST OVER THE NEXT 72 HOURS. ALTHOUGH THE CYCLONE IS FORECAST
TO REMAIN OVER 28C AND WARMER SSTS DURING THIS TIME...THE MID-LEVEL
ENVIRONMENT IS FORECAST TO GRADUALLY BECOME LESS MOIST. THE RESULT
IS THAT ONLY SLOW STRENGTHENING INTO A CATEGORY 1 OR 2 HURRICANE IS
EXPECTED. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE
PREVIOUS ADVISORY AND THE SHIPS INTENSITY MODEL...BUT IS MUCH LOWER
THAN THE HOT-TO-TROT HWRF MODEL...WHICH MAKES NORBERT A 119-KT
CATEGORY 4 HURRICANE IN 2-3 DAYS. IN CONTRAST...THE USUALLY ROBUST
GFDL MODEL BARELY BRINGS THE CYCLONE UP TO 70 KT IN 48 HOURS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      06/0300Z 14.1N 103.7W    55 KT
 12HR VT     06/1200Z 14.3N 104.6W    60 KT
 24HR VT     07/0000Z 14.7N 105.7W    65 KT
 36HR VT     07/1200Z 15.1N 107.0W    70 KT
 48HR VT     08/0000Z 15.7N 108.3W    75 KT
 72HR VT     09/0000Z 17.3N 110.5W    80 KT
 96HR VT     10/0000Z 19.5N 112.5W    75 KT
120HR VT     11/0000Z 23.0N 113.5W    65 KT
 
$$
FORECASTER STEWART
 
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