WDPN31 PGTW 210300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 02W (SURIGAE) WARNING NR 031//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 02W (SURIGAE), LOCATED APPROXIMATELY 295 NM NORTHEAST OF 
MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 05 KNOTS OVER THE 
PAST SIX HOURS. SURIGAE CONTINUES TO EXHIBIT A LARGE 65 NM EYE WITH 
A WARM CENTER. THE ENCIRCLING COLD RING OF DEEP CONVECTION HAS 
WARMED SLIGHTLY IN RECENT HOURS. THE CORE REMAINS LARGELY SYMMETRIC, 
AS VERTICAL WIND SHEAR (VWS) CONTINUES TO STAY UNDER 10 KTS, THOUGH 
SOME INCREASING DEFORMITY IS NOTED IN THE WESTERN SEMICIRCLE, 
PERHAPS DUE TO A NEARBY DRY AIR MASS OVER LUZON. THE INTENSITY IS 
HELD AT 120 KTS BASED ON A BLEND OF DVORAK INTENSITY ESTIMATES OF 
6.0 (115 KTS) FROM PGTW, T6.5 (127 KTS) FROM KNES, AND 112 KTS FROM 
ADT.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY 
SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B.  THROUGH 24 HOURS, SURIGAE WILL CONTINUE TRACKING NORTH-
NORTHWESTWARD TO THE EAST OF LUZON ALONG THE WESTERN PERIPHERY OF AN 
UPPER-LEVEL RIDGE TO THE EAST. THE LARGE AND STABLE CORE SIZE FAVORS 
LITTLE INTENSITY CHANGE UNTIL THE ATMOSPHERIC ENVIRONMENT BECOMES 
MORE HOSTILE. THIS IS EXPECTED TO OCCUR AFTER 24 HOURS AS A 
SHORTWAVE TROUGH WITHIN THE SUBTROPICAL JET (STJ) APPROACHES FROM 
SOUTHEASTERN CHINA, DRAMATICALLY INCREASING VERTICAL WIND SHEAR TO 
AROUND 30 KTS. STEADY WEAKENING IS EXPECTED TO ENSUE AFTER 24 HOURS 
AS THE TYPHOON ACCELERATES NORTHEASTWARD AND THEN EASTWARD INTO THE 
MID-LATITUDE WESTERLIES. BY AROUND 72 HOURS, THE AFOREMENTIONED 
SHORTWAVE IS EXPECTED TO INTERACT DIRECTLY WITH SURIGAE. MODEL 
SOLUTIONS DIVERGE AT THIS POINT, WITH VARYING DEGREES OF SYMBIOTIC 
INTERACTION BETWEEN THE SHORTWAVE AND THE TYPHOON, DEPENDING ON 
THEIR POSITIONS RELATIVE TO EACH OTHER. THE MORE FAVORABLE THE 
INTERACTION, THE FASTER AND STRONGER SURIGAE IS LIKELY TO BE. THE 
CURRENT FORECAST HEDGES BETWEEN THESE OUTCOMES, AS UNCERTAINTY 
INCREASES SUBSTANTIALLY IN TRACK AND INTENSITY BEGINNING AROUND 72 
HOURS. THE CURRENT FORECAST SHOWS WEAKENING TO 65 KTS AT 72 HOURS. 
THE TRACK FORECAST IS SIMILAR TO THE PREVIOUS ONE, WITH HIGH 
CONFIDENCE THROUGH 48 HOURS AND MODERATE CONFIDENCE THROUGH 72 HOURS.
   C. AFTER 72 HOURS, SURIGAE WILL INTERACT WITH A LOW-LEVEL THERMAL 
GRADIENT SOUTH OF JAPAN, AS WELL AS THE AFOREMENTIONED UPPER-LEVEL 
SHORTWAVE TO ITS NORTHWEST. WHILE MODELS DEPICT A RANGE OF POSSIBLE 
ARRANGEMENTS OF THESE FEATURES, THE INCREASINGLY BAROCLINIC 
ENVIRONMENT AROUND THE CYCLONE IS EXPECTED TO INDUCE THE ONSET OF 
EXTRATROPICAL TRANSITION (ET). THE FORECAST IS HIGHLY DEPENDENT ON 
THE DETAILS OF ET, AND THUS BOTH MODEL TRACK AND INTENSITY SPREAD IS 
HIGH AFTER 72 HOURS. THE CURRENT FORECAST TRACK IS SIMILAR TO THE 
PREVIOUS ONE, EXCEPT SLIGHTLY SLOWER AT 96 AND 120 HOURS DUE TO 
TRENDS IN THE MULTI-MODEL CONSENSUS. WEAKENING TO 45 KTS IS FORECAST 
BY 120 HOURS WITHIN A HIGH SHEAR ENVIRONMENT, BUT THIS FORECAST HAS 
BELOW-AVERAGE CONFIDENCE DUE TO THE AFOREMENTIONED RANGE OF ET 
EVOLUTIONS.//
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