WDPN31 PGTW 311500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 10W (SAOLA) WARNING NR 15//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 10W (SAOLA), LOCATED APPROXIMATELY 230 NM SOUTHEAST 
OF 
TAIPEI, TAIWAN, HAS TRACKED NORTHWESTWARD AT 08 KNOTS OVER THE PAST 
SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS
DEEP CONVECTIVE BANDING OVER THE SOUTHERN SEMI-CIRCLE OF THE LOW- 
LEVEL CIRCULATION CENTER (LLCC) WITH BUILDING TIGHTLY CURVED 
BANDING OVER THE NORTHERN PORTION. A 310902Z CORIOLIS 37 GHZ IMAGE 
DEPICTS THE VIGOROUS LLCC STRUCTURE WITH MULTIPLE FEEDER BANDS. TY 
10W CONTINUES TO MEANDER IN A GENERAL POLEWARD DIRECTION BUT HAS 
RECENTLY PICKED UP SPEED AND TAKEN A NORTHWESTWARD TRAJECTORY OVER 
THE LAST SIX HOURS. THE SYSTEM IS STILL IN A WEAK STEERING 
ENVIRONMENT WITH A NEAR EQUATORIAL RIDGE (NER) TO THE SOUTHEAST AND 
A SUBTROPICAL RIDGE (STR) TO THE NORTH. THE CURRENT POSITION IS 
BASED ON THE EIR AND PGTW FIX WITH GOOD CONFIDENCE. THE CURRENT 
INTENSITY IS BASED ON DVORAK ESTIMATES OF 65 KNOTS FROM PGTW, KNES, 
AND RJTD. UPPER-LEVEL ANALYSIS INDICATES A POINT SOURCE OF 
DIVERGENCE JUST SOUTHWEST OF TY 10W WHICH IS FLOWING INTO UPPER-
LEVEL TROUGHING FURTHER TO THE WEST. POLEWARD OUTFLOW IS NOW 
NONEXISTENT AND VERTICAL WIND SHEAR (VWS) HAS SLIGHTLY INCREASED TO 
10-15 KNOTS FROM THE NORTH. A LARGE AREA OF UPPER-LEVEL CONVERGENCE 
AND STRONG VWS RESIDES ROUGHLY ALONG 28N AND EXTENDS FROM THE 
MARIANAS TO EASTERN CHINA, AS EVIDENT IN THE ANIMATED WATER VAPOR 
IMAGERY. AS TY 10W GAINS LATITUDE AND TS 11W TRACKS CLOSER TO THE 
NORTH, IT SEEMS AS THOUGH IN THE LAST FEW FRAMES OF IMAGERY THAT 
OUTFLOW EASTWARD INTO THE TROUGHING MAY BE SLIGHTLY IMPROVING AND 
THE PRESSURE MAY BE SLIGHTLY EASING.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY 
FROM THE PREVIOUS PROGNOSTIC REASONING.
   B. TY 10W IS FORECAST TO SLOWLY DRIFT IN A GENERAL NORTHWARD 
DIRECTION UNDER THE INFLUENCE OF THE COMPETING STEERING MECHANISMS 
OVER THE NEXT 24-36 HOURS. AFTER TAU 36 THE STR TO THE NORTH IS 
EXPECTED TO BECOME THE MAIN STEERING INFLUENCE AND CAUSE AN 
INCREASE IN NORTHWESTWARD TRACK SPEED. UPPER-LEVEL CONDITIONS 
SHOULD GRADUALLY BECOME MORE FAVORABLE AND SEA SURFACE TEMPERATURES 
SHOULD PEAK NEAR 29C ALLOWING FOR TY 10W TO INTENSIFY NEAR A PEAK 
OF 100 KNOTS BY TAU 48. BY TAU 72 THE LLCC SHOULD BE OVERLAND AND 
BEGIN TO DISSIPATE DUE TO FRICTIONAL FORCES.
   C. BY TAU 96 TY 10W SHOULD HAVE DISSIPATED OVERLAND. NUMERICAL 
MODEL GUIDANCE CONTINUES TO COME INTO BETTER AGREEMENT IN TERMS OF 
THE TIMING OF THE NORTHWESTWARD TRACK DEFLECTION. THE EGRR REMAINS 
UNSTABLE AND ERRATIC AND THE JGSM AND ECMWF CONTINUE TO BE THE LEFT 
MOST OUTLIERS. THE OFFICIAL JTWC TRACK FORECAST IS SLIGHTLY FASTER 
THAN THE MODEL CONSENSUS (CONW) DURING THE FIRST TWO DAYS AND THEN 
REMAINS SLOWER IN THE EXTENDED FORECAST. THESE ADJUSTMENTS WERE 
MADE TO OFFSET THE EGRR UP TO TAU 48 AND THEN THE FASTER GFS AND 
GFDN FOR THE REMAINDER. TRACK FORECAST CONFIDENCE MUST CURRENTLY 
REMAIN LOW DUE TO THE WEAK STEERING ENVIRONMENT AND CAUTION IN THE 
NORTHWESTWARD TRACK MOTION TIMING.//
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