ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM 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 NNNN