WDPN31 PGTW 171500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 22W (PRAPIROON) 
WARNING NR 41//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 22W (PRAPIROON), LOCATED APPROXIMATELY 130 NM
SOUTHEAST OF KADENA AIR BASE, OKINAWA, JAPAN, HAS TRACKED
NORTHEASTWARD AT 14 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED 
INFRARED SATELLITE IMAGERY (EIR) SHOWS THE SYSTEM MAINTAINED SHALLOW
PERIPHERAL CONVECTION AROUND A WELL-DEFINED BUT FULLY EXPOSED LOW
LEVEL CIRCULATION CENTER (LLCC). THIS IS ALSO EVIDENT ON A 170835Z
SSMI-S MICROWAVE IMAGE THAT SHOWS A BROAD LLCC WITH WEAK CONVECTIVE
BANDS WRAPPING AT LEAST HALFWAY AROUND THE CENTER. THE INITIAL
POSITION IS BASED ON THE EIR LOOP AND THE MICROWAVE IMAGE WITH FAIR
CONFIDENCE. THE INITIAL INTENSITY OF 45 KNOTS IS SLIGHTLY HIGHER THAN
DVORAK ESTIMATES FROM RJTD AND PGTW TO REFLECT THE SUSTAINED TIGHT
BANDING. UPPER LEVEL ANALYSIS INDICATES THE SYSTEM IS DIRECTLY UNDER
A BREAK IN THE RIDGE AXIS IN AN AREA OF LOW (05-10 KNOT) VERTICAL
WIND SHEAR (VWS). WATER VAPOR ANIMATION SHOWS GOOD RADIAL OUTFLOW
WITH INCREASING STREAM ON THE POLEWARD CHANNEL. THE CYCLONE HAS
CRESTED THE WESTERN EDGE OF A DEEP SUBTROPICAL RIDGE (STR) ANCHORED
TO THE EAST. IT HAS BEGUN TO ACCELERATE NORTHEASTWARD IN RESPONSE TO
AN STR WEAKENED BY A MID-LATITUDE TROUGH DIGGING IN FROM THE YELLOW SEA.
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 48 AND BECOME A COLD CORE
LOW BY TAU 72. THE SYSTEM MAY INTENSIFY SLIGHTLY AS POLEWARD OUTFLOW
IMPROVES OVER THE NEXT 24 HOURS WITH THE STRONG WESTERLIES AHEAD OF
THE TROUGH. AFTERWARDS, INCREASING VWS AND COOLING SEA SURFACE
TEMPERATURES WILL GRADUALLY WEAKEN THE CYCLONE. THE NUMERIC MODEL
GUIDANCE IS IN VERY TIGHT AGREEMENT, LENDING HIGH CONFIDENCE TO THIS
FORECAST.    //
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