Tropical Storm KROVANH Advisory mer, 16.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (KROVANH) WARNING
NR 06//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 20W (KROVANH), LOCATED APPROXIMATELY 165 NM EAST-
NORTHEAST OF PAGAN, HAS TRACKED NORTHWESTWARD AT 09 KNOTS OVER
THE PAST SIX HOURS. THE CURRENT POSITION IS BASED ON A 152151Z GMI
IMAGE AND A 152332Z PGTW SATELLITE FIX. THE INTENSITY OF 45 KNOTS IS
CONSISTENT WITH SUBJECTIVE DVORAK AND AUTOMATED SATELLITE INTENSITY
ESTIMATES FROM MULTIPLE REPORTING AGENCIES. RECENT ANIMATED
MULTISPECTRAL SATELLITE IMAGERY SHOWS INCREASING ORGANIZATION, WITH
DEEP CONVECTIVE BANDING WRAPPING DIRECTLY INTO THE SYSTEM CENTER.
VERTICAL WIND SHEAR HAS DECREASED AS THE SYSTEM SHIFTED CLOSER TO AN
UPPER-LEVEL RIDGE AXIS DURING THE PAST SIX HOURS. TS 20W CONTINUES
TO TRACK ALONG THE PERIPHERY OF A SUBTROPICAL STEERING RIDGE TO THE
NORTH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 20W IS EXPECTED TO TRACK GENERALLY NORTHWESTWARD ALONG THE
PERIPHERY OF THE CURRENT STEERING RIDGE FOR THE NEXT 36 HOURS BEFORE
TURNING POLEWARD AND ROUNDING THE RIDGE AXIS THROUGH TAU 72. STEADY
INTENSIFICATION IS EXPECTED AS SYSTEM TRACKS OVER VERY WARM WATER,
VERTICAL WIND SHEAR DECREASES, AND POLEWARD OUTFLOW IMPROVES.
INTENSITY IS EXPECTED TO PEAK AROUND 105 KNOTS BETWEEN TAU 48 AND
TAU 72. HOWEVER, A PERIOD OF RAPID INTENSIFICATION AND HIGHER
MAXIMUM INTENSITY ARE POSSIBLE GIVEN FAVORABLE ENVIRONMENTAL
CONDITIONS.
   C. TS 20W IS EXPECTED TO ACCELERATE INTO THE MIDLATITUDE
BAROCLINIC ZONE AND BECOME EXTRATROPICAL IN THE EXTENDED FORECAST
PERIOD. INCREASING WESTERLY VERTICAL WIND SHEAR AND PASSAGE OVER
COOLER WATER WILL INDUCE SOME WEAKENING DURING THE TRANSITION.
DYNAMIC MODEL TRACK FORECASTS REMAIN IN FAIR AGREEMENT. SOME
ENSEMBLE GUIDANCE STILL TRACKS THE SYSTEM FARTHER TO THE WEST BEFORE
RECURVATURE, BUT THE JAPANESE ENSEMBLE MEAN HAS MOVED CLOSER TO THE
DETERMINISTIC GROUPING IN THE LATEST MODEL RUN.  HWRF, ON THE OTHER
SIDE OF THE GUIDANCE ENVELOPE, DEPICTS A TIGHTER RECURVATURE THAN
THE PRIMARY GROUPING. THE CURRENT OFFICIAL FORECAST LIES CLOSE TO
THE MULTI-MODEL CONSENSUS. GIVEN NOTED UNCERTAINTY IN ORIENTATION OF
THE RECURVATURE, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST.//
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