WDPN33 PGTW 010900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (KRATHON) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.9N 119.4E
   INITIAL INTENSITY: 125 KTS
   GEOGRAPHIC REFERENCE: 277 NM SOUTH-SOUTHWEST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 49 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A 22NM WIDE
EYE FEATURE WITH SUBSIDENT AIR CLEARING THE EYE CENTER. THE SETUP
OF AN EYEWALL REPLACEMENT CYCLE IS EVIDENT IN RADAR IMAGERY AS THE
SECONDARY EYEWALL HAS ALMOST COMPLETELY ENCIRCLED THE INNER EYE AND
THE NORTHWESTERN PORTION OF THE INNER EYE HAS BEGUN TO BREAK DOWN.
A 010528Z GCOM W1 AMSR2 89GHZ IMAGE SUPPORTS THE ANTICIPATED EYEWALL
REPLACEMENT CYCLE REVEALING A TELLTALE MOAT-LIKE FEATURE BETWEEN
THE SECONDARY EYEWALL AND INNER EYEWALL. WATER VAPOR IMAGERY
REVEALS STRONG EQUATORWARD OUTFLOW INTO DIFFLUENT UPPER-LEVEL FLOW.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
AFOREMENTIONED AMSR2 IMAGERY AND THE ANIMATED MSI. THE INITIAL
INTENSITY OF 125 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON
THE AGENCY AND OBJECTIVE FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT BETWEEN
A SUBTROPICAL RIDGE TO THE EAST AND WEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   RJTD: T7.0 - 140 KTS 
   KNES: T6.5 - 127 KTS
   DEMS: T7.0 - 140 KTS 
   CIMSS ADT: 129 KTS AT 010530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: HIGH UNCERTAINTY IN THE JTWC
MULTI-MODEL CONSENSUS CONTINUES TO CONTRIBUTE TO UNCERTAINTY IN THE
FORECAST TRACK AND INTENSITY.  

FORECAST DISCUSSION: TYPHOON (TY) 20W IS FORECAST TO TRACK
NORTHEASTWARD GRADUALLY FOR THE FIRST 36 HOURS OF THE FORECAST AS
IT REMAINS IN A COMPETING STEERING ENVIRONMENT. BETWEEN TAU 12-36,
AN UPPER-LEVEL TROUGH WILL WEAKEN THE STR TO THE WEST, ALLOWING FOR
THE STEERING ENVIRONMENT TO BE PICKED UP BY THE EASTERN STR. TY 20W
WILL MAKE LANDFALL BETWEEN TAU 36-48 AND CONTINUE TO WEAKEN OVER
LAND. BY THE TIME THE CIRCULATION COMES BACK OUT OVER WATER AT TAU
120, THE SYSTEM WILL BE WEAK AFTER INTERACTING WITH THE XUESHAN
MOUNTAIN RANGE OF NORTHERN TAIWAN. THE INTENSITY FORECAST REFLECTS
THE TRACK, WITH A SLIGHT DECREASE IN INTENSITY AS THE SYSTEM
REMAINS SLOW AND NEARLY QUASI-STATIONARY CAUSING SIGNIFICANT
UPWELLING OF COOLER WATER FOR THE FIRST 24 HOURS OF THE FORECAST.
AFTER LANDFALL, MORE DRASTIC AND CONTINUOUS WEAKENING IS EXPECTED
UNTIL THE SYSTEM WEAKENS TO 35KTS BY TAU 120. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE BIFURCATES BETWEEN
THE BULK OF THE JTWC MULTI-MODEL CONSENSUS MEMBERS TRACKING
NORTHEAST AND GFS AND GEFS TRACKING WEST. AN ALTERNATE SCENARIO
INDICATED BY GFS AND GEFS MODEL SOLUTIONS REPRESENT A COMPLETELY
DIFFERENT TRACK WHERE THE SYSTEM REMAINS QUASI-STATIONARY ENCASED
BETWEEN THE TWO SUBTROPICAL RIDGES AND WEAKEN DUE TO SIGNIFICANT
UPWELLING. THE SYSTEM WOULD LIKELY REMAIN NEARLY IN PLACE UNTIL THE
AFOREMENTIONED UPPER-LEVEL TROUGH ERODES THE WESTERN STR, ALLOWING
THE SYSTEM TO DRIFT WESTWARD WITH THE LOW-LEVEL FLOW. THE JTWC
INTENSITY GUIDANCE CLOSELY ALIGNS WITH GFS AS MOST MEMBERS ARE
GFS-BASED. THE JTWC TRACK AND INTENSITY FORECASTS ALIGN WITH THE
FIRST SCENARIO DUE TO THE MULTI-MODEL MEAN BUT HAS SLOWED THE TRACK
SPEED DUE TO THE UNCERTAINTY IN HOW LONG THE SYSTEM WILL REMAIN
QUASI-STATIONARY AND WHETHER IT WILL TRACK NORTHEASTWARD OR
WESTWARD. OVERALL, THE JTWC FORECAST CONFIDENCE IS EXTREMELY LOW.

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