WDPN33 PGTW 240300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (TWENTYSEVEN) 
WARNING NR 18//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM (TS) 27W (TWENTYSEVEN), LOCATED APPROXIMATELY 147 NM
SOUTH-SOUTHWEST OF ANDERSEN AFB, GUAM, HAS TRACKED NORTHWESTWARD AT
15 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) SHOWS THE MAIN CONVECTION HAS SHEARED SOUTHWARD
PARTIALLY EXPOSING A WEAK AND RAGGED LOW LEVEL CIRCULATION (LLC).
OVERALL, THE SYSTEM REMAINS BROAD AND DISORGANIZED AS DEEP BUT
FRAGMENTED CONVECTIVE BANDS, MOSTLY FROM THE SOUTH TO SOUTHWEST, FEED
LOOSELY INTO THE LLC. THE INITIAL POSITION IS BASED ON THE MSI LOOP
WITH GOOD CONFIDENCE.  AND IS SUPPORTED BY A 232056Z WINDSAT BULLSEYE
PASS. THE INITIAL INTENSITY OF 40 KNOTS IS HELD HIGHER THAN AGENCY
DVORAK ESTIMATES; HOWEVER, IT IS SUPPORTED BY SATCON DVORAK ESTIMATES
AND THE WINDSAT PASS. UPPER-LEVEL ANALYSIS INDICATES THE SYSTEM IS IN
AN AREA OF MODERATE (15-20 KNOT) NORTHERLY WIND SHEAR (VWS) THAT IS
PARTLY OFFSET BY EQUATORWARD OUTFLOW. HOWEVER, A TUTT CELL TO THE
NORTHEAST, JUST EAST OF GUAM, IS CAUSING SUBSIDENCE AND INHIBITING
POLEWARD OUTFLOW. SSTS IN THE REGION ARE VERY WARM AT 30 CELSIUS. THE
CYCLONE IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A BUILDING 
SUBTROPICAL RIDGE (STR) TO THE NORTHEAST.    
3. FORECAST REASONING.
   A. THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 27W WILL DEVELOP SLOWER THAN CLIMATOLOGICAL RATE OVER THE
NEXT THREE DAYS. HOWEVER, THE OVERALL FAVORABLE ENVIRONMENTAL
CONDITIONS WILL STILL INTENSIFY THE SYSTEM TO TYPHOON INTENSITY BY
TAU 48 AS IT TRACKS NORTHWESTWARD IN THE WARM PHILIPPINE SEA, STEERED
BY THE STR. AFTER TAU 48, HOWEVER, AS THE SYSTEM ENCOUNTERS STRONG
VWS AHEAD OF AN APPROACHING MID-LATITUDE TROUGH, THE INTENSITY WILL
BE SUSTAINED AT BEST, POSSIBLY EVEN REDUCED.   
   C. IN THE EXTENDED PERIOD, TS 27W WILL ROUND THE WESTERN EDGE OF
THE STR AND TURN MORE NORTHWARD THEN ACCELERATE NORTHEASTWARD, ON THE
FRONT EDGE OF THE AFOREMENTIONED MID-LATITUDE TROUGH. BY TAU 120 THE
CYCLONE WILL BE NEAR 30N, SOUTH OF HONSHU, JAPAN, AS IT BEGINS EXTRA
TROPICAL TRANSITION. INCREASED POLEWARD OUTFLOW ASSOCIATED WITH THE
MID-LATITUDE TROUGH AND IN PHASE-STORM MOTION WILL PROMOTE A
SECONDARY INTENSIFICATION PHASE, REACHING 80 KNOTS BY END OF
FORECAST. NUMERIC MODEL GUIDANCE SHOWS GOOD AGREEMENT UP TO TAU 48,
WITH JGSM AS THE RIGHTMOST OUTLIER. AFTER TAU 48 THE MODELS SPREAD
OUT SIGNIFICANTLY. IN VIEW OF THESE, THERE IS HIGH CONFIDENCE IN THE
JTWC TRACK FORECAST UP TO TAU 48, WHICH IS LAID JUST LEFT OF
CONSENSUS TO OFFSET JGSM, THEN LOW CONFIDENCE AFTERWARD.//
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