Tropical Storm NORBERT

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TROPICAL STORM NORBERT DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP152008
800 PM PDT SAT OCT 04 2008
 
DEEP CONVECTION HAS INCREASED AND BECOME BETTER ORGANIZED AROUND THE
LOW-LEVEL CENTER...AND THE DEPRESSION HAS STRENGTHENED INTO
TROPICAL STORM NORBERT. THE INITIAL INTENSITY OF 35 KT IS BASED ON
A DVORAK SATELLITE INTENSITY ESTIMATE OF T2.5/35 KT FORM TAFB...AND
A 04/1652Z ASCAT OVERPASS THAT CAME IN AFTER THE 21Z ADVISORY WAS
ISSUED...WHICH SHOWED SEVERAL 30- TO 34-KT WIND VECTORS IN THE
NORTHWEST QUADRANT. SINCE THAT THE TIME OF THE ASCAT OVERPASS...
HOWEVER...THE CONVECTIVE ORGANIZATION OF THE SYSTEM HAS IMPROVED.
 
THE INITIAL MOTION ESTIMATE IS 280/05. AVAILABLE MODEL GUIDANCE IS
IN GOOD AGREEMENT ABOUT A SLOW WESTWARD TO WEST-NORTHWESTWARD
MOTION THROUGH 96 HOURS AS NORBERT MOVES AROUND THE SOUTHWESTERN
PERIPHERY OF A SUBTROPICAL RIDGE FORECAST TO BUILD WESTWARD TO THE
NORTH OF THE CYCLONE. BY 120 HOURS...A SLOW TURN TOWARD THE
NORTHWEST IS EXPECTED AS A WEAK MID-LEVEL TROUGH IS FORECAST TO DIG
SOUTHWARD ALONG THE CALIFORNIA COAST AND ERODE THE WESTERN PORTION
OF THE MID-LEVEL RIDGE. THE OFFICIAL FORECAST TRACK IS CLOSE TO THE
PREVIOUS TRACK AND IS SLIGHTLY NORTH OF THE NHC MODEL CONSENSUS.
 
MODERATE VERTICAL SHEAR IS FORECAST TO WEAKEN THROUGH 72 HOURS AS
NORBERT REMAINS OVER SSTS GREATER THAN 28C. ALSO...AS NORBERT MOVES
FARTHER WEST...THE NEGATIVE EFFECTS OF DRY EASTERLY DOWNSLOPE AIR
COMING FROM THE GULF OF TEHUANTEPEC SHOULD BE REDUCED. THEREFORE...
GRADUAL STRENGTHENING IS FORECAST SIMILAR TO THE SHIPS AND ICON
INTENSITY MODELS. IT SHOULD BE NOTED THAT THE HWRF MODEL MAKES
NORBERT A 102-KT MAJOR HURRICANE ON DAY 4. HOWEVER...THIS SCENARIO
IS BEING DISCOUNTED AT THIS TIME DUE TO VERTICAL WIND SHEAR
EXPECTED TO INCREASE TO MORE THAN 20 KT AFTER 72 HOURS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      05/0300Z 14.2N 100.9W    35 KT
 12HR VT     05/1200Z 14.4N 101.8W    40 KT
 24HR VT     06/0000Z 14.7N 103.0W    45 KT
 36HR VT     06/1200Z 15.0N 104.0W    50 KT
 48HR VT     07/0000Z 15.4N 105.3W    55 KT
 72HR VT     08/0000Z 16.0N 107.0W    65 KT
 96HR VT     09/0000Z 17.0N 109.5W    65 KT
120HR VT     10/0000Z 18.5N 111.5W    65 KT
 
$$
FORECASTER STEWART
 
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