952 
 WTPZ45 KNHC 070247
 TCDEP5
 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
  
 $$
 FORECASTER BERG/STEWART