000
WTPZ45 KNHC 080257
TCDEP5
HURRICANE NORBERT DISCUSSION NUMBER  17
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP152008
800 PM PDT TUE OCT 07 2008

RECENT TRMM AND AMSU MICROWAVE DATA SHOW THAT NORBERT HAS A
WELL-DEFINED 20-25 N MI WIDE EYE AND A CLOSED EYEWALL.  THE EYE HAS
OCCASIONALLY APPEARED IN VISIBLE AND INFRARED IMAGERY AND IS
GRADUALLY BECOMING MORE DISTINCT WITH TIME.  THE EYEWALL CLOUD TOPS
EXCEED -80C IN SOME AREAS.  SATELLITE INTENSITY ESTIMATES ARE 90 KT
FROM TAFB AND SAB...AND THAT IS THE INITIAL INTENSITY FOR THIS
ADVISORY.  THE CIRRUS OUTFLOW IS GOOD IN ALL DIRECTIONS AT THIS
TIME.

THE INITIAL MOTION IS 290/8.  THERE IS LITTLE CHANGE IN THE TRACK
FORECAST PHILOSOPHY FROM THE LAST SEVERAL ADVISORIES.  NORBERT IS
ON THE SOUTHWEST SIDE OF A MID-LEVEL RIDGE OVER CENTRAL MEXICO. 
THE LARGE-SCALE MODELS FORECAST A LARGE DEEP-LAYER TROUGH TO
DEVELOP OVER THE WESTERN UNITED STATES AND ADJACENT WATERS BY 72-96
HR.  MOST TRACK GUIDANCE FORECASTS THIS TROUGH TO BE STRONG ENOUGH
TO RECURVE NORBERT NORTHEASTWARD INTO BAJA CALIFORNIA AND MAINLAND
MEXICO.  HOWEVER...THERE ARE TWO OUTSTANDING OUTLIERS IN THE GFS
AND ECMWF...WHICH FORECAST NORBERT TO MISS CONNECTIONS WITH THE
TROUGH AND TURN WESTWARD.  IN THE CASE OF THE GFS...IT APPEARS THAT
THE MODEL SHEARS THE HURRICANE APART...WHILE THE ECMWF LIFTS THE
TROUGH OUT BEFORE NORBERT CAN REACH IT.  THE NEW TRACK FORECAST
FOLLOWS THE SCENARIO OF THE OTHER DYNAMICAL GUIDANCE...CALLING FOR
NORBERT TO TURN NORTHWARD IN RESPONSE TO THE TROUGH BY 72 HR...AND
THEN CROSS BAJA CALIFORNIA INTO MAINLAND MEXICO.  THE NEW TRACK IS
FASTER THAN THE PREVIOUS TRACK AFTER 72 HR...BUT IS MUCH SLOWER
THAN THE NOGAPS...HWRF...GFDL...AND GFDN.  OVERALL THE NEW TRACK IS
IN BEST AGREEMENT WITH THE GUNA AND TCON CONSENSUS MODELS.

THE INTENSITY FORECAST IS A LITTLE TRICKY.  NORBERT SHOULD BE IN A
LIGHT SHEAR ENVIRONMENT FOR THE NEXT 60 HR OR SO...AND OVER SEA
SURFACE TEMPERATURES OF 28C OR HIGHER FOR 48 HR OR SO.  THIS...
COMBINED WITH THE CURRENT STRUCTURE AND COLD CLOUD TOPS...SUGGESTS
THE POSSIBILITY OF RAPID INTENSIFICATION.  INDEED...THE RAPID
INTENSIFICATION INDEX ATTACHED TO THE SHIPS MODEL HAS A 35 PERCENT
CHANCE OF 25 KT STRENGTHENING IN 24 HR...AND A 25 PERCENT CHANCE OF
35 KT STRENGTHENING.  ON THE OTHER HAND...MOST OF THE GUIDANCE
CALLS FOR THE HURRICANE TO PEAK AT ABOUT 105 KT INTENSITY IN 36 HR
OR SO...A LESS THAN RAPID INCREASE.  THE EXCEPTION TO THIS IS THE
HWRF...WHICH FORECASTS NORBERT TO REACH CATEGORY 4 STATUS.  BASED
ON CURRENT TRENDS... THE INTENSITY FORECAST NOW CALLS FOR NORBERT
TO BECOME A MAJOR HURRICANE...WITH A PEAK INTENSITY OF 110 KT IN
24-36 HR.  HOWEVER...IT WOULD BE NO SURPRISE IF IT GOT STRONGER. 
AFTER 48-60 HR...NORBERT SHOULD ENCOUNTER COOLER WATERS AND
SOUTHWESTERLY VERTICAL SHEAR...WHICH SHOULD CAUSE SOME WEAKENING
BEFORE THE SYSTEM REACHES BAJA CALIFORNIA.  NORBERT SHOULD WEAKEN
RAPIDLY AFTER LANDFALL IN MAINLAND MEXICO.
 
WHILE IT IS STILL PREMATURE TO SAY WHAT KIND OF IMPACT NORBERT MAY
HAVE ON BAJA CALIFORNIA...INTERESTS IN THE AREA...ESPECIALLY THE
SOUTHERN PENINSULA...SHOULD MONITOR THE PROGRESS OF NORBERT.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      08/0300Z 15.7N 109.0W    90 KT
 12HR VT     08/1200Z 16.1N 110.2W   100 KT
 24HR VT     09/0000Z 16.9N 111.5W   110 KT
 36HR VT     09/1200Z 17.8N 112.6W   110 KT
 48HR VT     10/0000Z 19.1N 113.4W   105 KT
 72HR VT     11/0000Z 22.5N 113.0W    95 KT
 96HR VT     12/0000Z 26.0N 111.0W    70 KT
120HR VT     13/0000Z 30.0N 108.5W    30 KT...INLAND
 
$$
FORECASTER BEVEN