WDPN33 PGTW 011500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (KRATHON) WARNING NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.3N 119.3E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 258 NM SOUTH-SOUTHWEST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 41 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS WARMING
CLOUD TOPS AND A CLOUD-FILLED EYE FEATURE THAT HAS WEAKENED OVER
THE LAST 12 HOURS AS EXPECTED WITH AN EARLIER EYEWALL REPLACEMENT
CYCLE THAT IS NOW COMPLETE. THE SLOW MOTION OF TYPHOON 20W HAS
CAUSED UPWELLING IN THE REGION AS WELL AS A DECREASE IN OCEAN HEAT
CONTENT WHICH ARE BOTH UNFAVORABLE FOR FURTHER INTENSIFICATION.
UPPER-LEVEL OUTFLOW REMAINS STRONG AND EQUATORWARD TOWARDS
DIFFLUENT NORTHEASTERLY FLOW. THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE BASED ON THE AFOREMENTIONED EYE FEATURE IN ANIMATED
EIR. THE INITIAL INTENSITY OF 110 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE AGENCY AND OBJECTIVE FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: COMPETING STEERING BETWEEN TWO
SUBTROPICAL RIDGES TO THE EAST AND WEST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   RJTD: T7.0 - 140 KTS 
   RCTP: T6.5 - 127 KTS
   KNES: T6.0 - 115 KTS
   DEMS: T7.0 - 140 KTS 
   CIMSS SATCON: 120 KTS AT 011023Z
   CIMSS ADT: 119 KTS AT 011130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

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: TY 20W WILL MEANDER NORTHEASTWARD WHILE
REMAINING IN A COMPETING STEERING ENVIRONMENT FOR THE NEXT 36
HOURS. BETWEEN TAU 24-48, A DEEP-LAYER TROUGH WILL ERODE THE
SUBTROPICAL RIDGE (STR) TO THE WEST, WHICH WILL ALLOW THE EASTERN
STR TO PICK UP THE STEERING ENVIRONMENT. AROUND TAU 36, THE SYSTEM
WILL MAKE LANDFALL, CAUSING THE SYSTEM TO WEAKEN AND BECOME SHALLOW
AS IT PASSES OVER THE MOUNTAINOUS TERRAIN OF TAIWAN. BY THE TIME
THE SYSTEM COMES BACK OUT OVER WATER, IT WILL BE A MEAGER 35KTS AND
MET WITH ELEVATED AND UNFAVORABLE SHEAR WEAKENING THE CIRCULATION.
THE TRACK IS FORECASTED WITH LOW CONFIDENCE BASED ON UNCERTAINTY IN
HOW LONG THE SYSTEM WILL REMAIN QUASI-STATIONARY IN THE COMPETING
STEERING ENVIRONMENT. THE INTENSITY WILL BE HIGHLY DEPENDENT ON THE
TRACK FORECAST AND HOW SIGNIFICANT THE UPWELLING IS DURING THE
INITIAL QUASI-STATIONARY PERIOD, AS WELL AS HOW LONG TOPOGRAPHIC
INTERACTION PERSISTS AFTER LANDFALL ON THE SOUTHWEST COAST OF
TAIWAN. 

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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