WDPN33 PGTW 030900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (KRATHON) WARNING NR 025//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.6N 120.4E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 162 NM SOUTH-SOUTHWEST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: OVER LAND

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS THE
TYPHOON 20W (KRATHON) MAKING LANDFALL NEAR THE CITY OF KAOHSIUNG,
TAIWAN. SPIRAL BANDS OF DEEP CONVECTION ARE SLOWLY THINNING, AS THE
SYSTEM TRACKS NORTH-NORTHEAST, INTO THE CENTRAL TAIWAN, ALONG THE
WESTERN SIDE OF THE CENTRAL MOUNTAIN RANGE. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON A RADAR LOOP, WHICH ALSO SHOWS
INTENSIFYING SOUTHWESTERLY SHEAR IMPACTING THE POLEWARD SECTOR OF
THE OUTFLOW. THE INITIAL INTENSITY OF 65 KTS IS ASSESSED WITH HIGH
CONFIDENCE BASED ON AGENCY AND AUTOMATED DVORAK ESTIMATES LISTED
BELOW, AS WELL AS THE DETERIORATION OF THE CONVECTIVE STRUCTURE
PRESENT OVER THE LAST 6 HOURS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   RJTD: T5.0 - 90 KTS
   RCTP: T4.0 - 65 KTS
   CIMSS SATCON: 78 KTS AT 030400Z
   CIMSS ADT: 61 KTS AT 0300400Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 15-20 KTS
   SST: OVER LAND
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

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: AS TY 20W MADE LANDFALL NEAR THE CITY OF
KAOHSIUNG IT IS FORECAST TO TURN NORTH-NORTHEASTWARD AND TRACK INTO
CENTRAL TAIWAN, UNDER THE INFLUENCE OF A STR TO THE EAST. HOWEVER,
BY TAU 24 THE PRIMARY STEERING WILL BE TAKEN OVER BY THE BUILDING
STR TO THE WEST, AS WELL AS AN ONGOING COLD SURGE EVENT, BRINGING
DRY AND COLD AIR THROUGH THE STRAIT OF TAIWAN. AS KRATHON TRANSITS
OVER LAND, THE UNFAVORABLE IMPACTS OF TERRAIN, AS WELL AS
INCREASING VERTICAL WIND SHEAR, WILL CAUSE FURTHER EROSION LEADING
TO A RAPIDLY DECREASING INTENSITY, REACHING 40 KTS BY TAU 24. AFTER
THAT, THE SYSTEM IS FORECAST TO BE STEERED WESTWARD AND BECOME
EMBEDDED IN THE LOW-LEVEL COLD SURGE, WITH FURTHER WEAKENING OF THE
CYCLONE CORE AND WIND FIELD, EVENTUALLY DISSIPATING BELOW 20 KTS BY
THE END OF THE FORECAST PERIOD. AFTER THE DISSIPATION OF 20W, 
ELEVATED WINDS IN THE TAIWAN STRAIT MAY PERSIST THAT ARE NOT 
ASSOCIATED WITH THE SYSTEM. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT IN
REGARD TO THE GENERAL TRACK OF THE SYSTEM, PRIOR TO ITS DISSIPATION
BACK OVER WATERS OF THE TAIWAN STRAIT BY TAU 48. PRIOR TO THAT
THERE IS REMAINING SIGNIFICANT DISCREPANCY IN THE TIMELINE OF THE
WESTWARD TURN, WITH SOME MODELS TAKING A RAPID TURN AT TAU 0
(NAVGEM), WHILE OTHERS TRACK THE SYSTEM INTO CENTRAL TAIWAN BEFORE
MAKING THE TURN (ECMWF, UKMET, GEFS). JTWC FORECAST IS PLACED WITH
MEDIUM CONFIDENCE, SLIGHTLY TO THE RIGHT OF THE MULTI-MODEL
CONSENSUS, BASED ON THE STRONGER CONFIDENCE IN THE ECMWF AND GEFS
ENSEMBLE RUNS. INTENSITY GUIDANCE REMAINS IN GOOD AGREEMENT
THROUGHOUT THE FORECAST, WITH ALL AIDS ESTIMATING STEADY WEAKENING.
THEREFORE, THE JTWC FORECAST IS PLACED NEAR THE MULTI-MODEL
CONSENSUS, LEADING TO DISSIPATION AT TAU 48.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
NNNN