HOME	ARCHIVES	FORECASTS	IMAGERY	ABOUT TPC	RECONNAISSANCE

ZCZC MIATCDEP2 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM ISELLE DISCUSSION NUMBER  10
NATIONAL WEATHER SERVICE MIAMI FL
2 AM PDT TUE SEP 17 2002

ISELLE CONTINUES TO GENERATE AN IMPRESSIVE AMOUNT OF COLD CONVECTIVE
TOPS.  HOWEVER...AN SSM/I OVERPASS AT 0323Z AND SHORTWAVE IR
IMAGES SUGGEST THAT THE CONVECTION IS MOSTLY IN THE WESTERN
SEMICIRCLE OF THE CIRCULATION.  SATELLITE INTENSITY ESTIMATES
ARE 65 KT FROM TAFB...55 KT FROM SAB...AND 45 KT FROM AFWA.
THE INITIAL INTENSITY IS SET TO 55 KT AS A COMPROMISE BETWEEN
THESE VALUES.  IT SHOULD BE NOTED THAT AN EARLIER QUIKSCAT OVERPASS
SHOWED 40 KT WINDS AT THE MOST...SO 55 KT MAY BE A LITTLE GENEROUS.

THE INITIAL MOTION IS 305/14.  WATER VAPOR IMAGERY INDICATES THAT
ISELLE IS ON THE SOUTH SIDE OF A MID-LEVEL RIDGE...WHICH IS
WEAKENING AS A LARGE DEEP-LAYER TROUGH MOVES INTO THE WESTERN
UNITED STATES.  LARGE-SCALE MODELS INDICATE THAT RIDGE SHOULD
WEAKEN FURTHER THROUGH THE FORECAST PERIOD...ALLOWING ISELLE TO
GRADUALLY TURN NORTHWARD OR POSSIBLY EVEN NORTHEASTWARD.  NHC TRACK
GUIDANCE SHOWS A RATHER LARGE SPREAD BY THE END OF THE FORECAST
PERIOD.  THE GFDN RECURVES ISELLE TO THE NORTHEAST...WHILE THE
GFDL SHOWS A NORTHERLY MOTION.  THE AVN TURNS THE STORM NORTH-
NORTHWESTWARD...WHILE THE BAMM...BAMS...AND NHC91 GO NORTHWESTWARD.
THE OTHER MODELS ARE SCATTERED IN BETWEEN.  SINCE THE TROUGH TO
THE NORTH IS FORECAST TO BYPASS ISELLE AND SOME RIDGING IS FORECAST
TO REMAIN TO THE EAST...THE FORECAST TRACK WILL CALL FOR A
NORTH-NORTHWESTWARD MOTION IN BEST AGREEMENT WITH THE AVN.

ISELLE SHOWS EXCELLENT OUTFLOW OVER THE WESTERN SEMICIRCLE AND FAIR
TO POOR OUTFLOW OVER THE EASTERN SEMICIRCLE.  VERTICAL SHEAR HAS
DECREASED DURING THE PAST 24 HR...SO UPPER-LEVEL CONDITIONS ARE
FAVORABLE FOR STRENGTHENING.  HOWEVER...THE STORM IS STARTING TO
MOVE OVER COOLER WATERS ...AND TIME IS RUNNING OUT FOR IT TO
STRENGTHEN.  THE INTENSITY FORECAST WILL CONTINUE TO CALL FOR
ISELLE TO BECOME A HURRICANE IN 24 HR...THEN BEGIN TO WEAKEN.
THIS IS IN AGREEMENT WITH THE SHIPS MODEL.

INITIAL AND 12 HR FORECAST WIND RADII HAVE BEEN REVISED SOMEWHAT
BASED ON THE SSM/I AND QUIKSCAT OVERPASSES.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     17/0900Z 21.0N 113.3W    55 KTS
12HR VT     17/1800Z 21.9N 114.7W    60 KTS
24HR VT     18/0600Z 22.6N 115.4W    65 KTS
36HR VT     18/1800Z 23.2N 116.0W    65 KTS
48HR VT     19/0600Z 23.8N 116.5W    60 KTS
72HR VT     20/0600Z 25.0N 117.0W    50 KTS
 
 
NNNN