WDPN31 PGTW 091500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (TALIM) WARNING 
NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 20W (TALIM), LOCATED APPROXIMATELY 156 NM NORTHWEST
OF ANDERSEN AFB, GUAM, HAS TRACKED WEST-NORTHWESTWARD AT 09 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY
SHOWS THE SYSTEM CONTINUED TO CONSOLIDATE AS FORMATIVE BANDS DEEPENED
AND WRAPPED TIGHTER INTO A BROAD AND OBSCURED LOW LEVEL CIRCULATION.
THE INITIAL POSITION IS EXTRAPOLATED WITH LOW CONFIDENCE ON A LARGE
LOW REFLECTIVITY CIRCULATION FEATURE IN THE 090826Z SSMIS MICROWAVE
PASS. THE INITIAL INTENSITY OF 35 KNOTS IS BASED ON OBJECTIVE AND
AGENCY DVORAK FIXES RANGING FROM T1.5 TO T2.9 AND REFLECTS THE
IMPROVED STATE OF THE SYSTEM. TS 20W IS TRACKING IN A FAVORABLE
ENVIRONMENT WITH STRONG EQUATORWARD OUTFLOW AND A STEADY EASTWARD
OUTFLOW INTO A TUTT CELL, LOW (10-15 KNOT) VERTICAL WIND SHEAR (VWS),
AND WARM SEA SURFACE TEMPERATURES (SSTS) IN THE PHILIPPINE SEA AT
30-31 CELSIUS. THE CYCLONE IS TRACKING ALONG THE SOUTHERN PERIPHERY
OF THE SUBTROPICAL RIDGE (STR) LOCATED TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE. 
   B. TS 20W WILL CONTINUE TO TRACK WEST-NORTHWESTWARD IN THE
PHILIPPINE SEA UNDER THE STEERING INFLUENCE OF THE STR. AS FAVORABLE
CONDITIONS PERSIST, THE SYSTEM WILL STEADILY THEN RAPIDLY INTENSIFY,
REACHING 90 KNOTS BY TAU 72.
   C. BEYOND TAU 72, TS TALIM WILL INITIALLY REMAIN ON A
WEST-NORTHWESTWARD TRACK UNDER THE STEERING INFLUENCE OF THE STR.
AFTER TAU 96, THE CYCLONE WILL TRACK MORE NORTHWESTWARD AS THE STR
WEAKENS AND RECEDES. TS 20W WILL CONTINUE TO INTENSIFY AT A RAPID
RATE AS VWS REMAINS LOW, SSTS STAY WARM AT 30 CELSIUS AND A ROBUST
OUTFLOW PERSISTS, PEAKING AT 115 KNOTS BY TAU 96 AS IT APPROACHES THE
SOUTHERN TIP OF TAIWAN. AFTERWARD, INTERACTION WITH SOUTHERN TAIWAN
AND EXPOSURE TO INCREASING VWS, EXACERBATED BY THE CROSS FLOW IN THE
TAIWAN STRAIT, WILL CAUSE RAPID DECAY - DOWN TO 85 KNOTS BY TAU 120.
AVAILABLE NUMERIC MODEL GUIDANCE IS IN GOOD AGREEMENT WITH NVGM AS
THE SOLE OUTLIER TO THE RIGHT OF THE MODEL ENVELOPE. THE JTWC
FORECAST IS LAID WITH FAIR CONFIDENCE SLIGHTLY LEFT OF CONW TO OFFSET
NVGM.//
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