WDPN33 PGTW 301500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (KRATHON) WARNING NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.5N 120.5E
   INITIAL INTENSITY: 125 KTS
   GEOGRAPHIC REFERENCE: 539 NM SOUTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 53 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS THE EYE
OF TYPHOON 20W (KRATHON) HAS BECOME MUCH MORE RAGGED AND SLIGHTLY
OBLONG SINCE THE LAST WARNING, BUT THE MICROWAVE EYE APPEARS
CIRCULAR BY COMPARISON. THE SYSTEM IS STRUCTURED WELL WITH
SYMMETRIC, SPIRAL BANDS OF CONVECTION AND ROBUST RADIAL OUTFLOW IN
AN ENVIRONMENT OF LOW VERTICAL WIND SHEAR. A 301011Z SSMIS
MICROWAVE IMAGE AND A 301009Z PARTIAL RCM-3 NRCS IMAGE DEPICT A
WELL-DEFINED EYE, CONSISTENT WITH THE HIGH-CONFIDENCE INITIAL
POSITION ASSESSMENT THAT WAS PLACED USING ANIMATED EIR IMAGERY AND
A 301200Z PGTW RADAR FIX. THE INITIAL INTENSITY WAS ASSESSED WITH
HIGH CONFIDENCE USING A BLEND OF AGENCY SUBJECTIVE DVORAK ESTIMATES
AND A 301009Z PARTIAL RCM-3 IMAGE THAT MEASURED MAXIMUM WINDS OF
125-126 KTS IN THE EASTERN EYEWALL.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: WEAK STEERING BY A DEEP-LAYER
SUBTROPICAL RIDGE TO THE DISTANT NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T6.0 - 115 KTS
   KNES: T6.5 - 127 KTS
   CIMSS SATCON: 112 KTS AT 301035Z
   CIMSS ADT: 117 KTS AT 301130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-31 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: ONSET OF LAND INTERACTION

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: GRADUAL SLOWING AND WEAKENING WILL OCCUR
IMMINENTLY IN PREPARATION FOR THE EXPECTED VECTOR CHANGE TO THE
NORTH. ERRATIC MOTION WILL BECOME INCREASINGLY LIKELY DURING THE
SLOW DOWN AND ESPECIALLY ONCE THE TYPHOON NEARS THE SOUTHWEST COAST
OF TAIWAN; MINIMAL LOOPS IN THE TRACK OR SOME FORM OF A LEESIDE
JUMP ACROSS TAIWAN CANNOT BE RULED OUT. THEREFORE, THE DWELL TIME
OVER TAIWAN AND THE PATH BEYOND TAU 48 IS PLAGUED WITH LARGE
UNCERTAINTIES THAT NEED TO BE TAKEN INTO CONSIDERATION AND ADJUSTED
AS THE SCENARIO UNFOLDS. THE BULK OF THE MODEL GUIDANCE SUPPORTS
THAT AN EMERGENCE OF 20W WILL TAKE PLACE SOMEWHERE ALONG THE
NORTHEASTERN COAST OF TAIWAN PRIOR TO TAU 72 AT A DRASTICALLY
WEAKENED STATE. GOING FORWARD, THE SYSTEM WILL WEAKEN AT A SLOW AND
GRADUAL PACE BUT LARGELY MAINTAIN STRENGTH THROUGH THE MAJORITY OF
THE FORECAST PERIOD. THE POSITION OF THE SYSTEM AT TAU 120 IS
FORECAST WITH INCREASING UNCERTAINTY DUE TO AMBIGUITY IN HOW A
WESTWARD-PROTRUDING SUBTROPICAL RIDGE TO THE EAST SITUATED OVER
JAPAN WILL INTERACT WITH AN APPROACHING MAJOR SHORTWAVE TROUGH FROM
THE NORTHWEST. 


MODEL DISCUSSION: GLOBAL ENSEMBLES ARE IN TIGHT AGREEMENT REGARDING
THE TRACK UNTIL AROUND TAU 72, WHERE A LARGE AMOUNT OF UNCERTAINTY
REMAINS. THE BULK OF THE GUIDANCE IS HINTING TOWARDS A
NORTH-NORTHEASTWARD TRACK THAT DEFLECTS TO THE WEST OR NORTHWEST
NEAR TAU 120, WITH VARIANCES IN THE PLACEMENT AND TIMING OF THAT
DEFLECTION. WITHOUT THE SUPPORT OF THE MAJOR SHORTWAVE TROUGH
DISCUSSED IN THE FORECAST REASONING, THERE WILL BE NO MECHANISM TO
RESTRENGTHEN THE SYSTEM. THEREFORE, THE ENSEMBLES ARE COMING INTO
BETTER AGREEMENT THAT THE SYSTEM WILL GRADUALLY WEAKEN THROUGH THE
END OF THE FORECAST PERIOD. OUTLIERS IN THE TRACK GUIDANCE SEEM TO
BE THE RESULT OF AN OVER-FORECASTED DECAY RATE WHICH SWITCHES THE
PRIMARY STEERING MECHANISM TO THE SUBTROPICAL RIDGE TO THE WEST,
WHICH IS MUCH CLOSER TO THE SYSTEM IN THE LOW LEVELS. HOWEVER, AT A
MORE REASONABLE RATE OF WEAKENING WHILE OVER TAIWAN, THE
SUBTROPICAL RIDGE TO THE EAST IS ABLE TO HANG ONTO THE STEERING
DOMINANCE, AND THIS IS REFLECTED BY THE BULK OF THE MODEL TRACKERS.
THE INTENSITY GUIDANCE IS IN RELATIVELY GOOD AGREEMENT WITH THE
RATE OF WEAKENING, AND MOST OF THE UNCERTAINTY RELATES TO THE DWELL
TIME OVER LAND. THE JTWC FORECAST ALIGNS CLOSELY WITH THE CONSENSUS
MEAN FOR TRACK AND INTENSITY.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: HIGH
   INTENSITY 72-120 HR: MEDIUM//
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