WDPN31 PGTW 231500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W (JELAWAT) WARNING NR 13//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 18W (JELAWAT), LOCATED APPROXIMATELY 470 NM EAST- 
SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTH-NORTHWESTWARD AT 
04 KNOTS OVER THE PAST SIX HOURS. TY 18W HAS RAPIDLY INTENSIFIED 
OVER THE PAST 24 HOURS WITH A 65 KNOT INCREASE (55 TO 120 KNOTS) 
AND, BASED ON ANIMATED INFRARED (IR) SATELLITE IMAGERY, HAS ALSO 
COMPLETED A SMALL COUNTER-CLOCKWISE LOOP FROM 07Z TO 09Z. ALTHOUGH 
GENERALLY POLEWARD, THE TRACK MOTION OVER THE PAST 12 HOURS HAS BEEN 
VERY ERRATIC AND THE MOTION OVER THE PAST TWO HOURS MAY BE SIGNALING 
ANOTHER LOOP. IR IMAGERY DEPICTS A RAPIDLY CONSOLIDATING SYSTEM WITH 
A 10NM ROUND EYE AND STRONG SPIRAL BANDING OVER THE WESTERN SEMI-
CIRCLE. THE INITIAL INTENSITY IS ASSESSED AT 120 KNOTS BASED ON 
DVORAK ESTIMATES RANGING FROM T6.0 (115 KNOTS) TO T6.5 (127 KNOTS) 
FROM PGTW AND KNES/RJTD, RESPECTIVELY. THERE IS GOOD CONFIDENCE IN 
THE INITIAL POSITION AND RECENT MOTION BASED ON THE SMALL EYE 
EVIDENT IN IR. TY 18W REMAINS EMBEDDED WITHIN A COMPLEX, WEAK 
STEERING ENVIRONMENT RESULTING FROM THE PERSISTENT TROUGHING PRESENT 
OVER ASIA AND THE PRESENCE OF A DEVELOPING LOW PRESSURE SYSTEM (93W) 
LOCATED ABOUT 695NM TO THE EAST-NORTHEAST. THE 23/00Z 500MB ANALYSIS 
DEPICTS A LARGE BREAK IN THE SUBTROPICAL RIDGE (STR) NORTH OF THE 
SYSTEM WITH A DEEP MIDLATITUDE SHORTWAVE TROUGH MOVING INTO WESTERN 
JAPAN AND A SHORTWAVE RIDGE MOVING INTO EASTERN CHINA. 
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
REASONING MESSAGE. DUE TO THE RAPID INTENSIFICATION, HOWEVER, THE 
PEAK INTENSITY IS NOW 140 KNOTS AT TAU 24.
   B. TY 18W IS FORECAST TO TRACK SLOWLY NORTHWARD THROUGH TAU 36 
UNDER THE STEERING INFLUENCE OF A BUILDING NEAR-EQUATORIAL RIDGE 
(NER) TO THE EAST. AS 93W TRACKS NORTHWARD, THE NER IS EXPECTED TO 
STRENGTHEN TO THE EAST AND NORTHEAST OF TY 18W, PROVIDING A 
NORTHWARD STEERING INFLUENCE. AFTER TAU 48, THE SHORTWAVE TROUGH 
WILL TRACK EASTWARD AND THE STR WILL BUILD NORTH OF THE SYSTEM, 
WHICH WILL ALLOW TY 18W TO TURN NORTHWESTWARD. DUE TO THE COMPLEX 
STEERING ENVIRONMENT, DYNAMIC MODEL GUIDANCE HAS CONTINUED TO REMAIN 
UNSTABLE WITH LARGE SHIFTS IN THE TRACK GUIDANCE FROM RUN-TO-RUN. 
THERE IS CURRENTLY A 300NM SPREAD IN SOLUTIONS AT TAU 72 WITH TWO 
DISTINCT MODEL GROUPINGS. THE EASTERN GROUP, COMPOSED OF UKMO, WBAR 
AND JGSM, INDICATES A NORTH-NORTHEASTWARD TRACK. THE WESTERN GROUP, 
COMPOSED OF GFDN, ECMWF, NOGAPS, ECMWF AND GFS, FAVORS A NORTH-
NORTHWESTWARD TO NORTHWESTWARD TRACK. THE JTWC FORECAST CONTINUES TO 
FAVOR THE WESTERN GROUP OF MODEL SOLUTIONS; HOWEVER, THERE IS LOW 
CONFIDENCE IN THE FORECAST TRACK. AVAILABLE ENSEMBLE GUIDANCE ALSO 
INDICATES A HIGH DEGREE OF UNCERTAINTY IN THE FORECAST TRACK WITH A 
SPREAD SIMILAR TO THE DETERMINISTIC SOLUTIONS. TY 18W IS EXPECTED TO 
PEAK NEAR TAU 24 AND SHOULD SEE GRADUAL WEAKENING THROUGH THE 
REMAINDER OF THE PERIOD AS POLEWARD FLOW WEAKENS.
   C. IN THE EXTENDED TAUS, THE DYNAMIC MODELS REMAIN CLUSTERED IN 
TWO GROUPS AND DIVERGE FURTHER WITH A 635NM SPREAD. THE JTWC 
FORECAST CONTINUES TO FAVOR THE WESTERN GROUP OF SOLUTIONS, WHICH 
INDICATE A NORTHWESTWARD TRACK TOWARD TAIWAN WITH A RE-CURVE POINT 
EAST OF TAIWAN. AFTER TAU 120, TY 18W IS FORECAST TO RE-CURVE TOWARD 
OKINAWA IN RESPONSE TO ANOTHER DEEP SHORTWAVE TROUGH, WHICH IS 
FORECAST TO TRACK INTO EASTERN CHINA AFTER TAU 96. THERE IS LOW 
CONFIDENCE IN THE EXTENDED TRACK DUE TO THE AFOREMENTIONED ISSUES.//
NNNN