WDPN31 PGTW 202100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 02W (SURIGAE) WARNING NR 030//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 02W (SURIGAE), LOCATED APPROXIMATELY 297 NM
EAST-NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD
AT 07 KTS OVER THE PAST SIX HOURS. SURIGAE CONTINUES TO EXHIBIT A 
LARGE 65 NM EYE, WHICH HAS WARMED IN RECENT HOURS. A REMNANT INNER 
RING OF 40 NM DIAMETER CONTINUES TO CIRCULATE ALONG THE INNER RIM OF 
THE PRIMARY EYEWALL. THE CORE REMAINS LARGELY SYMMETRIC, AS VERTICAL 
WIND SHEAR (VWS) CONTINUES TO STAY UNDER 10 KTS. SATELLITE-BASED 
INTENSITY ESTIMATES HAVE ASSUMED A WIDE RANGE OF VALUES OVER THE 
PAST 12 HOURS, RANGING FROM AS HIGH AS 130-135 KTS FROM EARLIER 
200930Z SMAP AND SAR PASSES, TO LOWER VALUES OF 116 KT FROM SATCON 
AND 110 KT FROM ADT. BASED ON A COMBINATION OF THESE ESTIMATES, 
ALONG WITH A 201800Z 6.0 (115 KTS) CURRENT INTENSITY ESTIMATE FROM 
PGTW, THE INITIAL INTENSITY IS HELD AT 120 KTS. THE TYPHOON'S 
OVERALL SATELLITE PRESENTATION HAS CHANGED LITTLE DURING THE PAST 24 
HOURS, SAVE FOR CONTINUING DISSOLUTION OF THE INNERMOST CONVECTIVE 
RING. 
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. SURIGAE'S FORWARD SPEED HAS 
INCREASED TO A SLIGHTLY BRISKER 07 KTS, WHICH IS LIKELY FAST ENOUGH 
TO PREVENT OCEAN COOLING BENEATH THE TYPHOON FROM CAUSING WEAKENING, 
BUT SLOW ENOUGH THAT INTENSIFICATION IS NOT EXPECTED. THE 
LARGE AND STABLE CORE SIZE ALSO FAVORS LITTLE INTENSITY CHANGE UNTIL 
THE ATMOSPHERIC ENVIRONMENT BECOMES MORE HOSTILE. THIS IS EXPECTED 
TO OCCUR BEGINNING AROUND 36 HOURS AS A SHORTWAVE TROUGH WITHIN THE 
SUBTROPICAL JET (STJ) APPROACHES FROM SOUTHEASTERN CHINA, 
DRAMATICALLY INCREASING VWS TO AROUND 30 KTS. STEADY WEAKENING IS 
EXPECTED TO ENSUE AFTER 36 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. THE GFS POSITIONS SURIGAE DIRECTLY BENEATH THE BASE OF THE 
SHORTWAVE, INDUCING RAPID WEAKENING AS THE TROUGH AXIS OUTRUNS THE 
TYPHOON. OTHER MODELS SUCH AS THE JAPANESE GSM AND CANADIAN GEM 
POSITION SURIGAE FARTHER AHEAD OF THE SHORTWAVE, ALLOWING INTENSITY 
TO REMAIN HIGHER FOR LONGER. THE CURRENT FORECAST SPLITS BETWEEN 
THESE OUTCOMES, SHOWING WEAKENING BELOW TYPHOON FORCE AFTER 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 HAS BEEN NUDGED 
SOUTHWARD AT 96 AND 120 HOURS TOWARD THE MULTI-MODEL CONSENSUS, 
WHICH HAS SHIFTED SOUTHWARD DURING THE PAST 24 HOURS. 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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