WDPN32 PGTW 121500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (RAMMASUN) WARNING 
NR 09//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 09W (RAMMASUN), LOCATED APPROXIMATELY 187 NM 
WEST OF ANDERSEN AFB, GUAM, HAS TRACKED WESTWARD AT 15 KNOTS OVER 
THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY 
(EIR) REVEALS DEEPENING CENTRAL CONVECTION AS THE BROKEN FORMATIVE 
BANDING ALONG THE LEADING WESTERN EDGE HAS BECOME MORE PERSISTENT 
AND THE LOW LEVEL CIRCULATION CENTER (LLCC) IS BEGINNING TO 
CONSOLIDATE. A 121205Z AMSU-B MICROWAVE IMAGE ADDITIONALLY SHOWS 
IMPROVED LOW LEVEL STRUCTURE AS IMPROVED BANDING CAN BE OBSERVED 
DESPITE AN OVERALL SMALL CONVECTIVE SIGNATURE. UPPER-LEVEL ANALYSIS 
REVEALS AN UNCHANGED, MARGINAL ENVIRONMENT CHARACTERIZED BY WEAKLY 
DIFFLUENT EASTERLY OUTFLOW AND LOW TO MODERATE (10 TO 15 KNOTS) 
VERTICAL WIND SHEAR (VWS). THERE IS LOW CONFIDENCE IN THE INITIAL 
POSITION DUE TO THE SOME AMBIGUITY IN THE EIR LOOP WHILE POSITION 
FIXES FROM ALL REPORTING AGENCIES REMAIN WIDELY SPREAD. THE CURRENT 
INTENSITY HAS BEEN INCREASED TO TROPICAL STORM STRENGTH (35 KNOTS) 
BASED ON THE IMPROVED LOW LEVEL STRUCTURE OF THE SYSTEM SEEN IN THE 
AFOREMENTIONED SATELLITE IMAGERY AND AS DVORAK INTENSITY ESTIMATES 
FROM PGTW AND RJTD HAVE INCREASED TO 35 KNOTS AS WELL. TS 09W 
CONTINUES TO TRACK ALONG THE SOUTHERN PERIPHERY OF A DEEP-LAYERED 
SUBTROPICAL RIDGE (STR) THAT IS ANCHORED TO THE NORTH OF THE SYSTEM.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST TRACK PHILOSOPHY FROM THE 
PREVIOUS PROGNOSTIC REASONING BULLETIN.
   B. TS 09W IS FORECAST TO TRACK WESTWARD FOR THE NEXT 72 HOURS 
ALONG THE SOUTHERN PERIPHERY OF THE ENTRENCHED STR. ENVIRONMENTAL 
CONDITIONS WILL REMAIN MARGINAL FOR THE NEXT 36 TO 48 HOURS, LEADING 
TO A SLOW INTENSIFICATION PROCESS. NEAR TAU 72, VWS WILL BEGIN TO 
DECREASE AND OUTFLOW WILL BEGIN TO IMPROVE ALLOWING FOR INCREASED 
INTENSIFICATION AS THE SYSTEM APPROACHES THE SOUTHWESTERN EDGE OF 
THE STR.
   C. AFTER TAU 72, A MID-LATITUDE TROUGH IS FORECAST TO DIG OVER 
EASTERN CHINA, WHICH WILL MODIFY THE STR, LEADING TO A MORE WEST-
NORTHWEST TRACK TOWARDS LUZON. FAVORABLE SEA SURFACE TEMPERATURES IN 
THE PHILIPPINE SEA ALONG WITH INCREASED OUTFLOW WILL LEAD TO A 
MAXIMUM INTENSITY AS THE SYSTEM APPROACHES LAND, REACHING 95 KNOTS 
BEFORE LANDFALL. AFTER LANDFALL, THE TERRAIN OF LUZON WILL 
SIGNIFICANTLY WEAKEN THE SYSTEM AS IT MOVES INTO THE SOUTH CHINA 
SEA. MODEL GUIDANCE IS IN GOOD AGREEMENT; HOWEVER, DUE TO THE LOW 
CONFIDENCE IN THE INITIAL POSITIONING, THE OVERALL CONFIDENCE IN THE 
FORECAST REMAINS LOW.//
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