WDPN33 PGTW 012100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (KRATHON) WARNING NR 019//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.5N 119.2E
   INITIAL INTENSITY: 105 KTS
   GEOGRAPHIC REFERENCE: 250 NM SOUTH-SOUTHWEST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
WELL-DEFINED INNER CONVECTIVE CORE WITH A COLD RING OF CLOUD TOPS
BETWEEN -70 AND -80 DEGREES CELSIUS ENCIRCLING A 20 NM DIAMETER
EYE. EYE TEMPERATURE HAS BEEN COOLING IN EIR IMAGERY, INDICATING
WEAKENING. A 011738Z AMSR-2 MICROWAVE IMAGE SHOWED EVIDENCE OF
CONCENTRIC EYEWALLS. BASED ON MOM6 OCEAN MODELLING FROM HAFS-A,
SIGNIFICANT OCEAN COOLING IS CURRENTLY OCCURRING BENEATH THE NEARLY
STATIONARY TYPHOON, LIKELY CONTRIBUTING TO THE ONGOING WEAKENING
TREND. UPPER-LEVEL OUTFLOW REMAINS EXPANSIVE IN ALL QUADRANTS WITH
LOW VALUES OF VERTICAL WIND SHEAR IN THE ENVIRONMENT. THE INITIAL
INTENSITY IS LOWERED TO 105 KT BASED ON A BLEND OF AGENCY DVORAK
ESTIMATES AND OBJECTIVE SATELLITE-BASED ESTIMATES RANGING FROM 95
TO 125 KT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   RJTD: T6.5 - 127 KTS
   RCTP: T6.5 - 127 KTS
   KNES: T5.5 - 102 KTS
   CIMSS SATCON: 112 KTS AT 011450Z
   CIMSS ADT: 94 KTS AT 011730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TYPHOON 20W (KRATHON) IS BARELY MOVING
SOUTHWEST OF TAIWAN, MIRED BETWEEN A SUBTROPICAL RIDGE TO ITS EAST
AND ANOTHER RIDGE OVER SOUTHERN CHINA AND NORTHERN VIETNAM. THE
SLOW MOVEMENT IS RESULTING IN DYNAMIC OCEAN COOLING BENEATH THE
TYPHOON ACCORDING TO NUMERICAL MODELING, WHICH IS LIKELY TO
CONTINUE OVER THE NEXT 24 HOURS, PROGRESSIVELY WEAKENING THE STORM.
THE TRACK FORECAST IS CHALLENGING DUE TO THE WEAK STEERING
CURRENTS, WITH NUMERICAL MODELS SPLIT OVER WHICH OF THE TWO RIDGES
WILL HAVE MORE INFLUENCE OVER TYPHOON KRATHON. THE ECMWF, UKMET,
GALWEM, HAFS-A, AND COAMPS-TC MODELS GENERALLY TRACK NORTHEASTWARD
TOWARD TAIWAN, WHILE THE GFS AND GFS ENSEMBLE MEAN TURN
SOUTHWESTWARD INTO A NORTHEASTERLY WIND SURGE BELT EXITING THE
TAIWAN STRAIGHT. IT IS WORTH NOTING THAT A SIGNIFICANT FRACTION OF
THE GFS ENSEMBLE MEMBERS MOVE NORTHEASTWARD WITH THE REST OF THE
MODEL GUIDANCE, CONTRIBUTING TO THE ASSESSMENT THAT THE GFS AND GFS
ENSEMBLE MEAN ARE OUTLIER SOLUTIONS. THE JTWC FORECAST THUS
MAINTAINS A SLOW, CRAWLING TRACK NORTHEASTWARD OVER TAIWAN, MAKING
LANDFALL IN JUST OVER 24 HOURS, SIMILAR TO THE PREVIOUS FORECAST.
OVERALL CONFIDENCE IS LOW, HOWEVER, GIVEN THAT SOME MODELS
ULTIMATELY TURN THE STORM WESTWARD ACROSS THE TAIWAN STRAIGHT,
WHILE OTHERS END UP NORTHEAST OF THE ISLAND IN 3 TO 4 DAYS. THE
INTENSITY FORECAST PRESUMES A TRACK OVER THE HIGH TERRAIN OF
TAIWAN, CAUSING STEEP WEAKENING AFTER 24 HOURS, ULTIMATELY
CULMINATING IN DISSIPATION AFTER MULTIPLE DAYS OVER LAND. HOWEVER,
MAX WINDS WEST AND NORTH OF THE CIRCULATION MAY REMAIN AT OR ABOVE
30 KT DUE TO A COOL SURGE EVENT CHANNELING THROUGH THE TAIWAN
STRAIGHT THROUGH 72 TO 96 HOURS. THE JTWC FORECAST THUS SHOWS
DISSIPATION AT AN INTENSITY OF 30 KT DUE TO THE CIRCULATION
BECOMING ILL-DEFINED AND ABSORBED INTO THE BROADER NORTHEASTERLY
SURGE AND ASSOCIATED FRONTAL ZONE. THIS EVOLUTION IS SUPPORTED BY
MOST GLOBAL MODELS THAT SHOW A TRACK OVER TAIWAN.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS CLOSE TO THE
MULTI-MODEL CONSENSUS THROUGH 24 HOURS, THEN BECOMES SLOWER OVER
TAIWAN AS THE CONSENSUS BECOMES SIGNIFICANTLY INFLUENCED BY OUTLIER
WESTERLY TRACKS. THE JTWC FORECAST IS CLOSE TO A BLEND OF THE
ECMWF, ECMWF ENSEMBLE MEAN, UKMET, AND THE CLUSTER OF GFS ENSEMBLE
MEMBERS WHICH MOVE OVER TAIWAN. THE JTWC INTENSITY FORECAST IS
BELOW THE MULTI-MODEL CONSENSUS AFTER 24 HOURS DUE TO THE
EXPECTATION OF LANDFALL IN TAIWAN, A SOLUTION NOT SHOWN BY
CONSENSUS MEMBERS THAT KEEP THE TYPHOON OVER THE SOUTH CHINA SEA,
MAKING THE CONSENSUS MEAN INTENSITY UNREPRESENTATIVE.

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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