Tropical Storm KROVANH Advisory 17 Σεπ.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (KROVANH) WARNING NR 09//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 20W (KROVANH), LOCATED APPROXIMATELY 356 NM
SOUTHEAST OF IWO TO, JAPAN HAS TRACKED WEST-NORTHWESTWARD AT 09
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY DEPICTS A DEEPENING CORE STRUCTURE WITH TIGHTLY CURVED
BANDING. A 161728Z SSMI 37GHZ MICROWAVE IMAGE SHOWS A SMALL 20NM
MICROWAVE EYE FEATURE WHILE THE 85GHZ IMAGE SHOWS INTENSE DEEP
CONVECTIVE BANDING ALONG THE NORTHERN PERIPHERY AND WRAPPING AROUND
THE WESTERN QUADRANT. THE WIND FIELD HAS BEEN ADJUSTED BASED ON A
161151Z ASCAT PASS. THE INITIAL POSITION IS BASED ON THE SMALL
MICROWAVE EYE FEATURE AND SUPPORTED BY SATELLITE FIXES FROM RJTD AND
PGTW WITH HIGH CONFIDENCE. THE CURRENT INTENSITY IS ASSESSED AT 65
KNOTS BASED ON CONCURRING DVORAK INTENSITY ESTIMATES OF T4.0 (65
KNOTS) FROM ALL AGENCIES AND SUPPORTS THE IMPROVED CONVECTIVE
SIGNATURE SEEN IN ALL AVAILABLE IMAGERY. 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 WEST-NORTHWESTWARD TO NORTHWESTWARD
TRAJECTORY ALONG THE SOUTHWESTERN PERIPHERY OF THE STEERING STR FOR
THE NEXT 24 HOURS BEFORE TURNING POLEWARD AND ROUNDING THE RIDGE
AXIS. VERY 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 105 KNOTS NEAR 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. DYNAMIC MODEL GUIDANCE IS IN OVERALL
GOOD AGREEMENT, LENDING TO HIGH CONFIDENCE IN THE JTWC TRACK
FORECAST.//
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