Hurricane NORBERT

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HURRICANE NORBERT DISCUSSION NUMBER  21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP152008
800 PM PDT WED OCT 08 2008

SATELLITE IMAGES CONTINUE TO DISPLAY A RATHER IMPRESSIVE TROPICAL
CYCLONE WITH A WELL-DEFINED EYE AND CIRRUS OUTFLOW FANNING AWAY
FROM THE CENTER.  ALTHOUGH CLOUD-TOP TEMPERATURES HAVE WARMED A
LITTLE IN THE EYEWALL RECENTLY...DVORAK SATELLITE CLASSIFICATIONS
HAVEN'T CHANGED...SO THE INITIAL INTENSITY IS LEFT AT 115 KT.  THE
HURRICANE SHOULD CONTINUE TO EXPERIENCE LIGHT SHEAR CONDITIONS AND
WARM WATERS FOR THE NEXT DAY OR SO.  THE SHEAR IS THEN FORECAST TO
INCREASE DUE TO AN APPROACHING UPPER-TROUGH AND...COMBINED WITH
SOME COOLER WATERS...THE HURRICANE SHOULD WEAKEN AS IT APPROACHES
LAND.  THE BIGGEST QUESTION IS HOW QUICKLY IT WILL LOSE STRENGTH. 
THE DYNAMICAL MODELS ARE SHOWING A MUCH STRONGER SYSTEM APPROACHING
BAJA CALIFORNIA WHILE THE STATISTICAL GUIDANCE SHOW A RATHER RAPID
DROP OFF IN THE WINDS.  THE INTENSITY FORECAST WILL BE SHADED A
LITTLE HIGHER THAN THE INTENSITY CONSENSUS AND IS SIMILAR TO THE
PREVIOUS FORECAST.  

THE HURRICANE HAS NOW TURNED TOWARD THE NORTHWEST AND IS MOVING AT
ABOUT 8 KT. NORBERT IS ROUNDING THE SOUTHWESTERN PERIPHERY OF
RIDGING OVER MEXICO.  LATE IN THE DAY TOMORROW...THE TROPICAL
CYCLONE SHOULD TURN TOWARD THE NORTH INTO A BREAK IN THE
SUBTROPICAL RIDGE.  ALL MODELS FORECAST A RATHER DEEP TROUGH DIVING
INTO THE WESTERN USA AND NORTHWESTERN MEXICO BY THE WEEKEND...
HOWEVER THERE IS A BIG DISCREPANCY ON HOW THE MODELS HANDLE THE
TROPICAL CYCLONE RESPONDING TO THE TROUGH.  THE CORE OF THE
DIFFERENCES REALLY REVOLVES AROUND IF THE NORBERT STAYS INTACT
UNDER INCREASING SHEAR.  AN INTACT SYSTEM WOULD LIKELY JUST
ACCELERATE NORTHEASTWARD AHEAD OF THE TROUGH...BUT A RAPIDLY
WEAKENING ONE MIGHT SHEAR APART AND LEAVE A WEAKER SYSTEM BEHIND
BEFORE A MEXICAN LANDFALL...LIKE THE GFS/ECMWF MODELS.  GIVEN HOW
STRONG THE SYSTEM IS NOW AND THE ENVIRONMENTAL CONDITIONS AHEAD OF
IT...NORBERT SEEMS UNLIKELY TO WEAKEN TO THAT DEGREE BEFORE
LANDFALL.  THUS...THE OFFICIAL FORECAST WILL LEAN ON THE FASTER
GUIDANCE AND GIVES LESS WEIGHT TO THE SLOWER SOLUTIONS OF THE GFS/
ECMWF MODELS.  THE NEW NHC FORECAST IS A LITTLE FASTER THAN THE
PREVIOUS ONE AND IS AHEAD OF THE DYNAMICAL MODEL CONSENSUS.  

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      09/0300Z 17.1N 111.8W   115 KT
 12HR VT     09/1200Z 17.8N 112.6W   115 KT
 24HR VT     10/0000Z 18.9N 113.4W   110 KT
 36HR VT     10/1200Z 20.5N 113.6W   100 KT
 48HR VT     11/0000Z 22.5N 113.2W    90 KT
 72HR VT     12/0000Z 28.0N 109.0W    45 KT...INLAND
 96HR VT     13/0000Z 35.0N 104.0W    20 KT...REMNANT LOW INLAND
120HR VT     14/0000Z...DISSIPATED
 
$$
FORECASTER BLAKE
 
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