Tropical Storm PRAPIROON Advisory Per, 18.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 22W (PRAPIROON) WARNING
NR 42//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 22W (PRAPIROON), LOCATED APPROXIMATELY 150 NM
EAST OF KADENA AIR BASE, OKINAWA, JAPAN, HAS TRACKED NORTHEASTWARD
AT 13 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
SATELLITE IMAGERY SHOWS A SINGULAR BAND OF DEEP CONVECTION LOCATED
ALONG THE NORTHWESTERN QUADRANT AND IS WRAPPING ALONG THE SOUTHERN
PERIPHERY TOWARDS THE LOW LEVEL CIRCULATION CENTER (LLCC). THE BAND
HAS BEEN FLARING OVER THE PAST 12 HOURS AND IS APPROACHING DIURNAL
MAXIMUM, WHICH IS HELPING TO ENHANCE THE IMPROVING POLEWARD OUTFLOW
CHANNEL. UPPER LEVEL ANALYSIS INDICATES THE LEADING EDGE OF AN
APPROACHING MID-LATITUDE TROUGH IS INCREASING THE EFFECTIVE POLEWARD
VENTING OF THE LLCC WITH AN ANTICYCLONE LOCATED TO THE EAST CREATING
A LOW VERTICAL WIND SHEAR (VWS) ENVIRONMENT. A TOTAL PRECIPITABLE
WATER (TPW) IMAGE INDICATES A DRY RIBBON OF AIR HAS COMPLETELY
SURROUNDED THE LLCC. THE DRY AIR HAS YET TO PENETRATE THE CENTER OF
THE LLCC, BUT A LOOP OF TPW IMAGERY SHOWS A DIMINISHING WARM, MOIST
AIR MASS AS THE LLCC HAS LOST CONTACT TO THE LARGER TROPICAL AIR
MASS TO THE SOUTH. THE SYSTEM IS BEING STEERED BY THE WESTERN EDGE
OF A DEEP SUBTROPICAL RIDGE (STR) ANCHORED TO THE EAST. IT HAS BEGUN
TO ACCELERATE NORTHEASTWARD IN RESPONSE TO THE TROUGH DIGGING ALONG
THE WESTERN EDGE OF THE STR.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
   B. TS PRAPIROON WILL CONTINUE TO ACCELERATE NORTHEASTWARD AND
BEGIN EXTRA-TROPICAL TRANSITION BEFORE TAU 36, BECOMING A COLD CORE
LOW BY TAU 72. THE SYSTEM IS FORECAST TO BRIEFLY INTENSIFY OVER THE
NEXT 12 HOURS DUE TO THE ENHANCED POLEWARD OUTFLOW, HOWEVER THIS
WILL BE SHORT LIVED WITH THE DECREASING SEA SURFACE TEMPERATURES,
LOST CONNECTION TO THE TROPICAL AIR MASS, AND INCREASING VWS BEYOND
TAU 12. BEYOND TAU 12 THE ENVIRONMENT WILL QUICKLY BECOME
UNFAVORABLE LEADING TO THE EXTRA-TROPICAL TRANSITION PROCESS TO
BEGIN. AVAILABLE NUMERIC MODEL GUIDANCE IS IN VERY TIGHT AGREEMENT,
LENDING HIGH CONFIDENCE FOR THIS FORECAST.//
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