000 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