000
WTPZ45 KNHC 091457
TCDEP5
HURRICANE NORBERT DISCUSSION NUMBER  23
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP152008
800 AM PDT THU OCT 09 2008
 
A 0906 UTC AMSR-E MICROWAVE PASS INDICATED THAT NORBERT MAY BE
UNDERGOING AN EYEWALL REPLACEMENT. HOWEVER...RECENT GEOSTATIONARY
SATELLITE IMAGERY SHOWS THE CONVECTION WITHIN THE INNER EYEWALL
MAKING A COMEBACK AND THE OUTER CONVECTIVE RING BECOMING LESS
DISTINCT. STILL...THE OVERALL CONVECTIVE PATTERN HAS THINNED...AND
CI NUMBERS FROM TAFB AND SAB AS WELL AS THE ADT HAVE FALLEN TO 5.5.
THE INITIAL INTENSITY IS ADJUSTED ACCORDINGLY TO 100 KT. THE
INTENSITY WILL LIKELY BE CONTROLLED BY INTERNAL DYNAMICS FOR THE
NEXT 12 HOURS OR SO IF IN FACT NORBERT IS GOING THROUGH AN EYEWALL
REPLACEMENT. SINCE FORECAST SKILL IN THESE SCENARIOS IS NOT THAT
GREAT...THE INTENSITY IS HELD AT 100 KT FOR THE SHORT TERM AS SEA
SURFACE TEMPERATURES REMAIN SUFFICIENTLY WARM AND VERTICAL SHEAR IS
LOW.  AFTER 36 HOURS OR SO...THE SHEAR IS EXPECTED TO INCREASE AS
NORBERT GETS CLOSER TO THE STRONG MID-LATITUDE TROUGH OVER THE
WESTERN UNITED STATES...AND WEAKENING IS EXPECTED AS THE HURRICANE
APPROACHES THE BAJA PENINSULA.

NORBERT HAS BEEN WOBBLING A LITTLE BIT BUT IS MOVING AT AN AVERAGE
MOTION OF 320/6.  IN GENERAL...THE TRACK GUIDANCE HAS SLOWED DOWN
DURING THE FIRST 48 HOURS...AND THE OFFICIAL FORECAST HAS ENDED UP
A LITTLE BEHIND THE PREVIOUS FORECAST.  ONLY THE GFS CONTINUES TO
SHOW NORBERT FAILING TO REACH THE BAJA PENINSULA DUE TO STRONG
VERTICAL SHEAR DECOUPLING THE SYSTEM...AND LEAVING THE LOW-LEVEL
CIRCULATION MEANDERING OFFSHORE.  WHILE THIS SCENARIO IS NOT OUT OF
THE QUESTION...IT HAS HAPPENED BEFORE...THE NHC FORECAST CONTINUES
TO LIE CLOSE TO THE CONSENSUS OF THE OTHER MODELS AND STILL BRINGS
NORBERT ACROSS THE BAJA PENINSULA TO MAINLAND MEXICO.  A 96-HOUR
POSITION IS NO LONGER GIVEN SINCE IT IS UNLIKELY THAT A LOW-LEVEL
CENTER WOULD BE ABLE TO SURVIVE THE HIGH RUGGED TERRAIN OF
NORTHWESTERN MEXICO.  HOWEVER...THE MID-LEVEL REMNANTS AND THE
ASSOCIATED RAINFALL WILL LIKELY SPREAD OVER NORTHERN MEXICO AND THE
SOUTH-CENTRAL UNITED STATES BY DAY 4 AND 5.
 
AN AIR FORCE RECONNAISSANCE HURRICANE HUNTER AIRCRAFT IS SCHEDULED
TO INVESTIGATE NORBERT LATER THIS AFTERNOON. A HURRICANE WATCH WILL
LIKELY BE REQUIRED FOR PORTIONS OF SOUTHWESTERN BAJA CALIFORNIA
LATER TODAY OR TONIGHT.
 

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      09/1500Z 18.0N 112.7W   100 KT
 12HR VT     10/0000Z 18.6N 113.4W   100 KT
 24HR VT     10/1200Z 19.8N 114.0W   100 KT
 36HR VT     11/0000Z 21.5N 113.9W    90 KT
 48HR VT     11/1200Z 23.1N 112.9W    80 KT
 72HR VT     12/1200Z 27.5N 109.5W    35 KT...INLAND
 96HR VT     13/1200Z...DISSIPATED INLAND
 
$$
FORECASTER BERG