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National Hurricane Center Discussion

Data from the Plymouth State College (PSC) Weather Center
URL: http://vortex.plymouth.edu




770 


WTNT43 KNHC 270234


TCDAT3


HURRICANE MITCH DISCUSSION NUMBER  22


NATIONAL WEATHER SERVICE MIAMI FL


10 PM EST MON OCT 26 1998





THE EYE CONTINUES TO BE EXTREMELY WELL-DEFINED AND THE UPPER-


TROPOSPHERIC OUTFLOW REMAINS VERY IMPRESSIVE.  LATEST DVORAK


CLASSIFICATIONS FROM SAB IN WASHINGTON AND THE TPC CONTINUE TO


SUPPORT A CURRENT INTENSITY OF 155 KNOTS...HOWEVER THERE HAS
BEEN


SOME EROSION OF THE COLD CLOUD TOPS OVER THE NORTHWEST
SEMICIRCLE OF


THE HURRICANE...WHICH IS BELIEVED TO BE A TEMPORARY CONDITION. 
IT


IS VERY UNUSUAL FOR HURRICANES TO MAINTAIN SUCH GREAT INTENSITY
FOR


VERY LONG...BUT HURRICANES SUCH AS THESE ARE RARE EVENTS
THEMSELVES.





MITCH WILL LIKELY REMAIN AN EXTREMELY DANGEROUS HURRICANE FOR AT


LEAST A DAY OR TWO.  THE MAIN FACTOR GOVERNING WHETHER MITCH
WILL


MAINTAIN SUCH INTENSITY...OTHER THAN EYEWALL REPLACEMENT CYCLES


WHICH CAN CAUSE SHORT-TERM FLUCTUATIONS...IS INCREASED VERTICAL


SHEAR.  THIS SHEAR MAY BE PRODUCED BY STRONGER UPPER-LEVEL


WESTERLIES TO THE NORTH OF THE HURRICANE...WHICH COULD
EVENTUALLY


IMPINGE ON MITCH.





MOTION CONTINUES TOWARD THE WEST-NORTHWEST.  OUR TRACK
PREDICTION


GUIDANCE CONTINUES TO BE ANYTHING BUT STRAIGHTFORWARD.  THE 500
MB


HIGH OVER THE GULF OF MEXICO COULD CONTINUE TO PUSH MITCH ON A


WEST-NORTHWESTWARD TO WESTWARD PATH TOWARD BELIZE OR
YUCATAN...AND


THIS IS SHOWN BY THE BETA/ADVECTION MODELS AND THE U.K. MET.
OFFICE


GLOBAL MODEL.  ON THE OTHER HAND THE NCEP GLOBAL
MODEL...NOGAPS...


AND THE BAROTROPIC MODEL SHOW A TURN TO THE NORTH IN A COUPLE OF


DAYS.  THE LATTER TRACK IS CONSISTENT WITH A SUBTLE WESTWARD
SHIFT


OF THE ABOVEMENTIONED RIDGE IN THE MODEL FORECAST...WHICH COULD


LEAVE A SLIGHT OPENING TO THE NORTH OF MITCH.  THE LATEST GFDL
RUN


SHOWS A SLOW MEANDERING MOTION DEVELOPING IN 12 TO 24
HOURS...AND


PERSISTING THROUGH 72 HOURS.  THE OFFICIAL TRACK FORECAST...LIKE
THE


PREVIOUS ONE...SHOWS A SLOWING OF THE FORWARD SPEED IN 12 HOURS
OR


SO WITH A GRADUAL TURN TO THE NORTH IN A COUPLE OF DAYS.  THE


LONGER-TERM MOVEMENT OF MITCH REMAINS SHROUDED IN UNCERTAINTY.





IT IS INTERESTING TO NOTE THAT...BASED ON THE 905 MB CENTRAL


PRESSURE MEASURED FROM THE AIRCRAFT EARLIER TODAY...MITCH IS
TIED AS


THE FOURTH STRONGEST HURRICANE OBSERVED IN THE ATLANTIC BASIN. 
HERE


ARE THE RANKINGS:





GILBERT (1988)...888 MB


UNNAMED (1935)...892 MB


ALLEN   (1980)...899 MB


CAMILLE (1969)...905 MB


MITCH   (1998)...905 MB





PASCH


   


FORECAST POSITIONS AND MAX WINDS


 


INITIAL     27/0300Z 17.4N  84.1W   155 KTS


12HR VT     27/1200Z 17.7N  85.0W   155 KTS


24HR VT     28/0000Z 18.0N  85.5W   150 KTS


36HR VT     28/1200Z 18.2N  85.8W   140 KTS


48HR VT     29/0000Z 18.5N  86.0W   135 KTS


72HR VT     30/0000Z 19.0N  86.0W   125 KTS