Tropical Storm KROVANH Advisory jeu, 17.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (KROVANH) WARNING NR 10//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 20W (KROVANH), LOCATED APPROXIMATELY 290 NM
SOUTHEAST OF IWO TO, JAPAN HAS TRACKED NORTHWESTWARD AT 11 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
DEPICTS A SYMMETRIC CORE STRUCTURE WITH DEEP SPIRAL BANDING WRAPPING
INTO A 20NM CLOUD FILLED EYE WHICH SUPPORTS THE INITIAL POSITION
WITH HIGH CONFIDENCE. A 162105Z WINDSAT MICROWAVE IMAGE CONTINUES TO
SHOW AN IMPROVED CONVECTIVE STRUCTURE WITH A CONSTRICTING MICROWAVE
EYE. THE INTENSITY HAS BEEN INCREASED TO 80 KNOTS BASED ON AN
ASSESSMENT OF DVORAK INTENSITY ESTIMATES AND REFLECTS THE IMPROVED
STRUCTURE OF THE TYPHOON. ENVIRONMENTAL ANALYSIS INDICATES A VERY
FAVORABLE ENVIRONMENT WITH NEAR RADIAL OUTFLOW, LOW (5-10 KNOT)
VERTICAL WIND SHEAR (VWS), AND SEA SURFACE TEMPERATURES (SSTS) NEAR
30 CELSIUS. TY 20W IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A
DEEP-LAYERED SUB-TROPICAL RIDGE (STR) TO THE NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 20W WILL TRACK ON A NORTHWESTWARD TRAJECTORY ALONG THE
SOUTHWESTERN PERIPHERY OF THE STEERING STR FOR THE NEXT 24 HOURS
BEFORE TURNING POLEWARD AND ROUNDING THE STR AXIS. FAVORABLE
ENVIRONMENTAL CONDITIONS WILL SUPPORT RAPID INTENSIFICATION FOR THE
NEXT 24 HOURS. BEYOND TAU 24, VWS WILL INCREASE TO GREATER THAN 20
KNOTS DUE TO AN APPROACHING MID-LATITUDE TROUGH FROM THE WEST.
INITIALLY THE AFOREMENTIONED TROUGH WILL PROVIDE AN ENHANCED
POLEWARD OUTFLOW CHANNEL, ALLOWING TY KROVANH TO PEAK AT 115 KNOTS
BY TAU 36. AFTERWARDS THE INCREASED VWS WILL BEGIN TO WEAKEN THE
SYSTEM.
   C. IN THE EXTENDED TAUS, TY 20W WILL TRACK TO THE NORTHEAST FOR
THE REMAINDER OF THE FORECAST PERIOD. INCREASING VWS AND COOLER SSTS
WILL CONTINUE TO WEAKEN THE SYSTEM AS IT ACCELERATES INTO THE WEAK
MID-LATITUDE BAROCLINIC ZONE. THE SYSTEM IS FORECAST TO BEGIN EXTRA-
TROPICAL TRANSITION (ETT) AT TAU 96 AND COMPLETE ETT BY THE END OF
THE FORECAST PERIOD. DYNAMIC MODEL GUIDANCE CONTINUES TO BE IN
OVERALL GOOD AGREEMENT, LENDING TO HIGH CONFIDENCE IN THE JTWC TRACK
FORECAST.//
NNNN
NNNN