Tropical Storm KROVANH Advisory пт, 18.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (KROVANH) WARNING NR 13//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 20W (KROVANH), LOCATED APPROXIMATELY 141 NM
SOUTHEAST OF IWO TO, JAPAN HAS TRACKED NORTHWESTWARD AT 10 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY SHOWS AN ENLARGED 27NM EYE SURROUNDED BY A CONVECTIVE CORE
STRUCTURE THAT IS STRUGGLING RECENTLY DUE TO DRY AIR ALONG THE
WESTERN PERIPHERY PULLING INTO THE CIRCULATION. A 171616Z AMSR-2
36GHZ MICROWAVE IMAGE SHOWS A SMALL 15NM MICROWAVE EYE FEATURE WITH
THE BULK OF CONVECTION CONFINED ALONG THE NORTHERN PERIPHERY. THE
INITIAL POSITION IS BASED ON THE EYE POSITION IN THE AFOREMENTIONED
IMAGERY WITH HIGH CONFIDENCE. THE CURRENT INTENSITY HAS BEEN
INCREASED TO 105 KNOTS BASED ON AN ASSESSMENT OF DVORAK INTENSITY
ESTIMATES FROM ALL AGENCIES AND INITIAL SIGNS OF INTENSIFICATION
OVER THE PAST SIX HOURS. UPPER LEVEL ANALYSIS INDICATES A MARGINALLY
FAVORABLE ENVIRONMENT WITH EXCELLENT DIVERGENCE ALOFT BUT INCREASING
VERTICAL WIND SHEAR (VWS) DUE TO A MID-LATITUDE TROUGH TO THE WEST.
SEA SURFACE TEMPERATURES (SSTS) REMAIN VERY FAVORABLE. TY 20W IS
TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A DEEP-LAYERED SUB-
TROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 20W WILL CONTINUE TO TRACK ON A NORTHWESTWARD TRAJECTORY
FOR THE NEXT 12 HOURS BEFORE TURNING POLEWARD, ROUNDING THE STR
AXIS, AND TRACKING TO THE NORTHEAST. MARGINALLY FAVORABLE
ENVIRONMENTAL CONDITIONS WILL PERSIST FOR THE NEXT 12 HOURS ALLOWING
TY KROVANH TO INTENSIFY SLIGHTLY. BEYOND TAU 24, CONTINUED DRY AIR
ENTRAINMENT AND INCREASING VWS WILL BEGIN TO WEAKEN THE TYPHOON.
SSTS WILL DROP BELOW 26 CELSIUS JUST AFTER TAU 48 WHICH WILL
INCREASE THE RATE OF WEAKENING. DYNAMIC MODEL GUIDANCE IS IN VERY
TIGHT AGREEMENT THROUGH THIS PORTION OF THE FORECAST PERIOD.
   C. IN THE EXTENDED TAUS, TY KROVANH WILL CONTINUE TO TRACK TO THE
NORTHEAST AROUND THE STR. 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 AT TAU 96 AND CONTINUE THROUGH THE END OF THE
FORECAST PERIOD. DYNAMIC MODEL GUIDANCE DIVERGES IN THIS PORTION OF
THE FORECAST DUE TO A COMPLEX STEERING ENVIRONMENT WHICH COULD CAUSE
THE SYSTEM TO BECOME QUASI-STATIONARY. ALTHOUGH THE MODEL GUIDANCE
IS STRUGGLING TO DETERMINE A SOLUTION IN THE EXTENDED FORECAST, THE
TIGHT AGREEMENT IN THE FIRST 72 HOURS, LENDS TO HIGH CONFIDENCE IN
THE JTWC TRACK FORECAST.//
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