Hurricane NORBERT
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HURRICANE NORBERT DISCUSSION NUMBER 13
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP152008
800 PM PDT MON OCT 06 2008
NORBERT HAS BEEN PRODUCING A SOLID MASS OF DEEP CONVECTION WITH
CLOUD TOPS COLDER THAN -80C OVER THE PAST SEVERAL HOURS. DVORAK
INTENSITY ESTIMATES FROM TAFB AND SAB REMAIN AT T4.0...AND THE ADT
ESTIMATE FROM UW-CIMSS IS ALSO NEAR T4.0. A COMPARISON OF 91 AND 37
GHZ CHANNELS FROM A 0003 UTC SSMIS PASS INDICATES THAT THE
CIRCULATION MAY BE TILTED A LITTLE WESTWARD WITH HEIGHT DUE TO
EASTERLY SHEAR...BUT IT DOES APPEAR THAT AN EYEWALL HAS DEVELOPED
AROUND THE CENTER. THEREFORE...NORBERT IS UPGRADED TO A HURRICANE
WITH 65-KT WINDS.
NORBERT HAS BEEN MOVING STEADILY WEST-NORTHWESTWARD AT 285/7. THE
TRACK FORECAST REASONING HAS CHANGED VERY LITTLE AND CONTINUES TO
SHOW NORBERT MOVING WEST-NORTHWEST OVER THE NEXT 48 HOURS OR
SO...THEN TURNING NORTH AND NORTH-NORTHEASTWARD AROUND A MID-LEVEL
RIDGE CENTERED OVER MEXICO FROM DAY 3 THROUGH 5. MOST OF THE MODELS
ARE TIGHTLY-CLUSTERED WITH A FEW EXCEPTIONS. THE GFS CONTINUES TO
SHOW THE DISTURBANCE NEAR THE COAST OF EL SALVADOR BECOMING THE
DOMINANT CIRCULATION OVER THE NEXT FEW DAYS AND DOWNPLAYS THE
EXISTENCE OF NORBERT. SINCE THAT SOLUTION HAS BEEN WRONG FOR
SEVERAL DAYS...THE GFS IS DISCOUNTED IN THIS FORECAST. THE HWRF HAS
ALSO BEEN DISCOUNTED SINCE IT SHOWS A WIDER AND FASTER SWING AROUND
THE MID-LEVEL RIDGE...BRINGING THE SYSTEM TO WESTERN TEXAS BY DAY
5. THE NHC OFFICIAL FORECAST IS VERY CLOSE TO THE CONSENSUS OF THE
OTHER MODELS...AND IS JUST A LITTLE BIT EAST OF THE PREVIOUS
FORECAST AT THE LATTER END OF THE PERIOD.
EASTERLY TO SOUTHEASTERLY SHEAR IS EXPECTED TO CONTINUE TO INFLUENCE
NORBERT OVER THE NEXT 48 HOURS BEFORE IT REACHES THE MID-LEVEL
RIDGE AXIS...SO ONLY MODEST STRENGTHENING IS ANTICIPATED DURING
THAT TIME FRAME. THIS IS MORE OR LESS IN LINE WITH THE SHIPS AND
LGEM MODELS. HOWEVER...SHIPS BEGINS TO WEAKEN NORBERT BY 72 HOURS
DUE TO THE IDIOSYNCRASIES OF THE GFS AND ITS OVERLY ENTHUSIASTIC
DEVELOPMENT OF THE OTHER DISTURBANCE. DISREGARDING THAT
CONTRIBUTION IN THE SHIPS MODEL...THE OFFICIAL FORECAST KEEPS
NORBERT AT 80 KT AT DAY 3. THEREAFTER...SOUTHWESTERLY SHEAR IS
EXPECTED TO INCREASE AS NORBERT IS PICKED UP BY A LARGE UPPER
TROUGH OVER THE WESTERN UNITED STATES...AND GRADUAL WEAKENING
SHOULD ENSUE AS THE SYSTEM APPROACHES THE BAJA PENINSULA.
FORECAST POSITIONS AND MAX WINDS
INITIAL 07/0300Z 14.7N 105.9W 65 KT
12HR VT 07/1200Z 15.0N 106.9W 70 KT
24HR VT 08/0000Z 15.4N 108.3W 75 KT
36HR VT 08/1200Z 15.9N 109.6W 80 KT
48HR VT 09/0000Z 16.6N 110.9W 80 KT
72HR VT 10/0000Z 18.5N 112.5W 80 KT
96HR VT 11/0000Z 21.5N 112.5W 70 KT
120HR VT 12/0000Z 24.5N 111.0W 60 KT...INLAND BAJA CALIFORNIA
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FORECASTER BERG/STEWART
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