Hurricane NORBERT
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HURRICANE NORBERT DISCUSSION NUMBER 20
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP152008
200 PM PDT WED OCT 08 2008
NORBERT IS A VERY IMPRESSIVE-LOOKING HURRICANE WITH VERY COLD CLOUD
TOPS SURROUNDING A RATHER SYMMETRIC 30-35 NM WIDE EYE. A 1709 UTC
AMSU OVERPASS SUGGEST THAT NORBERT MAY BE ATTEMPTING TO DEVELOP
CONCENTRIC EYEWALLS...BUT THERE HAVE NOT BEEN ANY ADDITIONAL
MICROWAVE IMAGERY TO CORROBORATE THIS. SUBJECTIVE DVORAK INTENSITY
ESTIMATES FROM TAFB AND SAB ARE A CONSENSUS T6.0 OR 115 KT...WHICH
IS USED FOR THE INITIAL INTENSITY.
ENVIRONMENTAL CONDITIONS ARE FORECAST TO REMAIN FAVORABLE FOR
ANOTHER DAY OR SO...AND INTENSITY CHANGES DURING THIS TIME WILL
LIKELY BE DETERMINED BY INNER-CORE STRUCTURE...WHICH IS TYPICALLY
DIFFICULT TO PREDICT. THE INTENSITY FORECAST ALLOWS FOR SOME
SLIGHT ADDITIONAL INTENSIFICATION IN THE NEAR TERM. THEREAFTER
NORBERT WILL BE MOVING OVER SLIGHTLY COOLER WATERS...WHICH IS
EXPECTED TO INITIATE GRADUAL WEAKENING. IT IS MUCH TOO EARLY TO
DETERMINE HOW STRONG NORBERT WILL BE WHEN IT APPROACHES THE BAJA
PENINSULA. IF NORBERT MOVE A LITTLE SLOWER AND TRACKS WEST OF THE
CURRENT FORECAST IT WOULD SPEND MORE TIME OVER COOLER WATERS...
THAN A FASTER AND MORE EASTWARD TRACK. IN ADDITION TO THE TRACK
FORECAST DILEMMA...SOUTHWESTERLY SHEAR IS PREDICTED TO INCREASE
AROUND THE TIME NORBERT APPROACHES BAJA CALIFORNIA. GIVEN THESE
UNCERTAINTIES...THE OFFICIAL FORECAST IS CLOSE THE INTENSITY
CONSENSUS AND IS NOT AS STRONG AS THE MORE AGGRESSIVE HWRF MODEL
WHICH KEEPS NORBERT RATHER STRONG UNTIL FINAL LANDFALL IN MAINLAND
MEXICO.
THE INITIAL MOTION REMAINS THE SAME AS EARLIER TODAY...290/8 KT. THE
TRACK GUIDANCE IS IN GENERALLY GOOD AGREEMENT THAT A NORTHWESTWARD
MOTION SHOULD COMMENCE SOON...AS NORBERT BEGINS TO ROUND THE
SOUTHWESTERN PERIPHERY OF A MID-LEVEL RIDGE LOCATED OVER NORTHERN
MEXICO. THEREAFTER...NORBERT SHOULD TURN NORTHWARD...THEN
NORTHEASTWARD AHEAD OF A DEEP-LAYER TROUGH MOVING INTO THE WESTERN
UNITED STATES IN A COUPLE OF DAYS. WHILE THE GUIDANCE AGREES ON
THIS SCENARIO...THERE CONTINUES TO BE A VERY LARGE SPREAD ON THE
FORWARD MOTION OF THE HURRICANE IN 2-3 DAYS. FOR EXAMPLE...AT 72
HOURS...THE GFS...ECMWF...GFDN...AND UKMET ALL SHOW NORBERT NEAR OR
SOUTHWEST OF THE BAJA COAST...WHILE THE GFDL...HWRF AND NOGAPS
PREDICT THAT NORBERT WILL BE OVER MAINLAND MEXICO AT THAT TIME.
SOME OF THESE DIFFERENCE ARE LIKELY IN RESPONSE TO HOW STRONG OR
DEEP THE VARIOUS MODELS KEEP NORBERT. GIVEN THE LARGE SPREAD...THE
NHC FORECAST REMAINS NEAR THE MODEL CONSENSUS UNTIL IT IS MORE
CLEAR AS TO WHICH ONE OF THESE SOLUTIONS WILL PREVAIL. THE NEW
FORECAST IS NEARLY IDENTICAL TO THE PREVIOUS ADVISORY.
THE WIND RADII HAVE BEEN EXPANDED SLIGHTLY ON THE BASIS OF DATA FROM
A QUIKSCAT OVERPASS.
FORECAST POSITIONS AND MAX WINDS
INITIAL 08/2100Z 16.6N 111.2W 115 KT
12HR VT 09/0600Z 17.2N 112.1W 120 KT
24HR VT 09/1800Z 18.3N 113.0W 115 KT
36HR VT 10/0600Z 19.7N 113.5W 105 KT
48HR VT 10/1800Z 21.5N 113.3W 95 KT
72HR VT 11/1800Z 26.0N 110.5W 70 KT
96HR VT 12/1800Z 32.0N 106.0W 25 KT...REMNANT LOW INLAND
120HR VT 13/1800Z...DISSIPATED
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FORECASTER BROWN
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