Hurricane ISABEL

ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER  23
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT THU SEP 11 2003
 
ISABEL HAS CONTINUED TO INTENSIFY TODAY.  DVORAK T-NUMBERS FROM ALL
3 AGENCIES...TAFB...SAB...AND AFWA ARE NOW 7.0 AND OBJECTIVE
T-NUMBERS ARE ALSO ABOUT THE SAME VALUE.  THIS SUPPORTS A CURRENT
INTENSITY ESTIMATE OF 140 KT...A CATEGORY 5 ON THE SAFFIR-SIMPSON
HURRICANE SCALE.  HURRICANES RARELY MAINTAIN SUCH STRENGTH FOR VERY
LONG...AND ISABEL MAY NOT STAY A CAT 5 FOR EVEN AS LONG AS SHOWN
HERE.  THERE IS AN UPPER-LEVEL CYCLONE ABOUT 15 DEGREES TO THE
WEST-NORTHWEST OF THE HURRICANE BUT THIS SYSTEM APPEARS TO BE
NARROWING AND IF THIS TREND CONTINUES...IT SHOULD NOT HAVE MUCH OF
AN IMPACT ON THE INTENSITY OF ISABEL.  ANOTHER POSSIBLE FACTOR IS
THE COOLED SST WAKE PRODUCED BY HURRICANE FABIAN IN THE VICINITY OF
63W.  SINCE THERE DO NOT TO BE ANY MAJOR INHIBITING FACTORS IN THE
ENVIRONMENT...INTERNAL DYNAMICS SUCH AS EYEWALL REPLACEMENT CYCLES
WILL PROBABLY HAVE THE GREATEST INFLUENCE ON INTENSITY CHANGE.  THE
OFFICIAL FORECAST ASSUMES THAT WE WILL CONTINUE TO HAVE A MAJOR
HURRICANE ON OUR HANDS THROUGHOUT THE FORECAST PERIOD.

MOTION CONTINUES AT ABOUT 280/8...ALONG WITH SOME MINOR TROCHOIDAL
WOBBLES.  A DEEP-LAYER HIGH PRESSURE AREA TO THE NORTH OF ISABEL IS
LIKELY TO MAINTAIN THE SLOW WESTWARD TO WEST-NORTHWESTWARD STEERING
OVER THE NEXT SEVERAL DAYS.  THE CURRENT NHC FORECAST IS SOMEWHAT
SLOWER THAN THE PREVIOUS ONE...BUT FASTER THAN THE GUNA CONSENSUS. 
THIS IS FAIRLY CLOSE TO THE LATEST U.K. MET OFFICE TRACK.  THE
LATTER MODEL IS THE WESTERNMOST OF THE GUIDANCE SUITE.

THE BIG QUESTION CONTINUES TO BE WHAT WILL HAPPEN BEYOND THE 5-DAY
FORECAST PERIOD.  IT IS STILL IMPOSSIBLE TO STATE WITH ANY
CONFIDENCE WHETHER A SPECIFIC AREA ALONG THE U.S. COAST WILL BE
IMPACTED BY ISABEL.  THIS WILL LIKELY DEPEND ON THE RELATIVE
STRENGTH AND POSITIONING OF A MID-TROPOSPHERIC RIDGE NEAR THE EAST
COAST AND A MID-LATITUDE TROUGH TO THE WEST OR NORTHWEST AROUND THE
MIDDLE OF NEXT WEEK.  UNFORTUNATELY...WE HAVE LITTLE SKILL IN
PREDICTING THE EVOLUTION OF STEERING FEATURES AT THESE LONG RANGES. 

FORECASTER PASCH
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      11/2100Z 21.6N  55.3W   140 KT
 12HR VT     12/0600Z 21.7N  56.7W   140 KT
 24HR VT     12/1800Z 21.9N  58.6W   135 KT
 36HR VT     13/0600Z 22.4N  60.5W   130 KT
 48HR VT     13/1800Z 22.9N  62.3W   125 KT
 72HR VT     14/1800Z 24.0N  65.5W   115 KT
 96HR VT     15/1800Z 25.0N  68.5W   115 KT
120HR VT     16/1800Z 26.0N  71.5W   115 KT
 
NNNN