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HURRICANE ISIDORE DISCUSSION NUMBER  27
NATIONAL WEATHER SERVICE MIAMI FL
5 PM EDT SUN SEP 22 2002
 
AIR FORCE RESERVE HURRICANE HUNTERS FOUND A MINIMUM PRESSURE OF 935
MB...UP 1 MB FROM 7 HOURS AGO. AGAIN...THIS PRESSURE WOULD GENERALLY 
CORRESPOND TO ABOUT 128 KT AND CATEGORY 4 INTENSITY.  ALL THREE 
SATELLITE AGENCIES CONTINUE TO REPORT A DVORAK SATELLITE INTENSITY 
ESTIMATE OF T6.5...OR 127 KT. A DROPSONDE IN THE SOUTHEAST QUADRANT 
JUST NORTH OF THE YUCATAN COAST CAME IN WITH 108 KT. ONE COULD ARGUE 
THAT SINCE THIS WAS AN OFFSHORE WIND THAT STRONGER WINDS TO CATEGORY 
4 STRENGTH COULD EXIST TO THE NORTH OF THE CENTER OVER THE WATER. 
HOWEVER...THE BACKGROUND PRESSURE IS UNUSALLY LOWER THAN NORMAL...SO 
THE TYPICAL PRESSURE-WIND RELATIONSHIP MAY NOT APPLY TO ISIDORE THE 
SAME WAY IT DID NOT APPLY TO HURRICANE FLOYD IN 1999. RECON IS STILL 
INVESTIGATING ISIDORE AND THEY ARE SCHEDULED TO PUNCH THROUGH THE 
NORTHERN EYEWALL DURING THE HOUR TO SEE IF STRONGER WINDS EXIST.
 
THE INITIAL MOTION ESTIMATE IS 260/07. THERE IS A SIGNIFICANT CHANGE 
TO THE PREVIOUS FORECAST TRACK AFTER 48 HOURS. ISIDORE IS EXPECTED 
TO CONTINUE MOVING WEST-SOUTHWESTWARD UNDER THE INFLUENCE OF A VERY 
NARROW AND WEAK...5870 METERS AT 500 MB...MID-LEVEL RIDGE THAT 
EXTENDS FROM NEAR BROWNSVILLE TEXAS NORTHEASTWARD ALONG THE GULF 
COAST TO THE CAROLINAS. THE SHORTWAVE TROUGH THAT WAS MENTIONED 
YESTERDAY OVER THE PACIFIC NORTHWEST THAT THE MODELS DID NOT 
INITIALIZE WELL SHOWED UP QUITE NICELY TODAY IN THE 12Z UPEPR-AIR 
DATA AS A SMALL CLOSED LOW OVER CENTRAL TEXAS. A 30-35 KT SPEED MAX 
ON THE WEST SIDE OF THE LOW SHOULD HELP TO DIG THE LOW SOUTHWARD 
INTO SOUTHERN TEXAS AND NORTHEAST MEXICO AND EFFECTIVELY WEAKEN AND 
EVENTUALLY ERODE THE WEAK RIDGE AXIS OVER THE WESTERN GULF. THIS 
SHOULD ALLOW ISIDORE TO GRADUALLY GAIN LATITUDE AFTER ABOUT 24 TO 36 
HOURS AND EVENTUALLY MOVE NORTHWARD AT A FASTER SPEED OF AROUND 10 
KT BY 72 HOURS. BOTH THE AVN AND GFDL MODELS HAVE ABANDONED THEIR 
PREVIOUSLY CONSISTENT SHARP SOUTHWEST MOTION AROUND THE WESTERN 
YUCATAN AND DEEP INTO THE BAY OF CAMPECHE. ALL OF THE GLOBAL MODELS 
ARE NOW IN GOOD AGREEMENT ON QUICKLY BREAKING DOWN THE RIDGE ALONG 
THE CENTRAL AND WESTERN GULF COAST AS A STRONGER SHORTWAVE TROUGH 
ENTERS THE SOUTHERN PLAINS BY 48 HOURS. THE RIDGE ACROSS FLORIDA AND 
THE SOUTHEAST UNITED STATES IS FORECAST TO STRENGTHEN...WHICH SHOULD 
HELP TO GRADUALLY TURN ISIDORE TO THE NORTHWEST AND THEN NORTHWARD 
AFTER 48 HOURS. THE OFFICIAL TRACK IS CLOSE THE PREVIOUS TRACK 
THROUGH 48 HOURS...AND THEN IS TO THE RIGHT OF AND FASTER AFTER 
THAT. THIS IS SIMILAR TO THE AVN-AVN ENSEMBLE-UKMET-GFDL CONSENSUS. 
IT IS NOTEWORHTY TO MENTION THAT THE NOGAPS MODEL HAS BEEN 
ADVERTISING A MORE NORTHWARD TURN FOR THE LAST 2 DAYS...BUT IT 
APPEARS TO BE A LITTLE TOO FAR EAST AT THIS TIME.
 
THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS INTENSITY FORECAST.
SOME ADDITIONAL INTENSIFICATION IS POSSIBLE DUE TO THE LOW SHEAR AND 
ABUNDANCE OF WARM GULF WATER UP TO ABOUT 28N LATITUDE. THE SHIPS 
INTENSITY MODEL BRINGS ISIDORE TO 131 KT IN 48 HOURS...WITH ONLY 
VERY SLOW WEAKENING AFTER THAT. NOTE...THE WIND RADII WERE EXPANDED 
SICNE ISIDORE IS ALREADY A LARGER THAN AVERAGE ATLANTIC 
HURRICANE...AND IS EXPECTED TO GROW EVEN LARGER BY 72 HOURS.
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     22/2100Z 21.5N  89.2W   110 KTS
12HR VT     23/0600Z 21.4N  90.2W   110 KTS
24HR VT     23/1800Z 21.4N  91.3W   110 KTS
36HR VT     24/0600Z 21.5N  92.0W   115 KTS
48HR VT     24/1800Z 22.3N  92.7W   125 KTS
72HR VT     25/1800Z 25.0N  93.0W   125 KTS
 
 
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