WDPN33 PGTW 300900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (KRATHON) WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.5N 121.2E
   INITIAL INTENSITY: 120 KTS
   GEOGRAPHIC REFERENCE: 511 NM SOUTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 51 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
WELL-FORMED, CIRCULAR APPEARANCE WITH STRIATED TEXTURE IN THE CLOUD
TOPS THROUGHOUT THE EYEWALL REGION AND A CONTRACTING EYE, OCCLUDED
IN THE CENTER WITH LOW-BASED CLOUDS. DEEP CONVECTION IS CONTINUING
TO FORM IN THE WELL-WRAPPED SPIRAL BANDS, PARTICULARLY ALONG THE
SOUTHERN PERIPHERY AND EASTERN EYEWALL. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE EYE POSITION AND SUPPORTED
BY EXTRAPOLATION FROM A 300252Z COWVR 34 GHZ MICROWAVE IMAGE. THE
NORTHWESTWARD MOVEMENT HAS CONTINUED TO BE TROCHOIDAL AS THE SYSTEM
EXPERIENCED ADDITIONAL STRENGTHENING SINCE THE PREVIOUS WARNING.
TYPHOON KRATHON IS GENERATING STRONG RADIAL OUTFLOW, WITH ASSISANCE
IN THE EQUATORWARD DIRECTION BY MODERATE NORTHEASTERLY FLOW ALOFT
OVER THE PHILIPPINES. AGENCY SUBJECTIVE DVORAK ESTIMATES SAT IN
GOOD AGREEMENT WITH THE RANGE OF OBJECTIVE INTENSITY ESTIMATES
LISTED BELOW, WHICH ALLOWED FOR A HIGH-CONFIDENCE CURRENT INTENSITY
ASSESSMENT. THIS WAS ALSO SUPPORTED BY A 300445Z AMSR2 MAXIMUM WIND
OF 122 KTS IN THE EYEWALL.

INITIAL WIND RADII BASIS: AMSR2 DATA

CURRENT STEERING MECHANISM: 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
   DEMS: T6.0 - 115 KTS
   CIMSS SATCON: 116 KTS AT 300330Z
   CIMSS ADT: 122 KTS AT 300530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-31 CELSIUS
   OUTFLOW: STRONG RADIAL

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: TYPHOON KRATHON WILL CONTINUE DRIFTING
NORTHWESTWARD AT A SLOW CLIP AND MAY BEGIN EXHIBITING MORE ERRATIC
MOTION (IN ADDITION TO THE TROCHOIDAL MOTION ALREADY OBSERVED) AS
IT PREPARES TO MAKE ITS EXPECTED PIVOT TO THE NORTHEAST. THE ONSET
OF LAND INTERACTION WITH SOUTHERN TAIWAN BETWEEN TAU 36 AND TAU 48
WILL INITIATE THE WEAKENING PROCESS. IT IS CLIMATOLOGICALLY COMMON
FOR TYPHOONS IN THIS REGION TO DISPLAY ERRATIC AND POSSIBLY A
LOOPING TRACK MOTION, AS WELL AS POTENTIAL FOR A LEESIDE JUMP TO
OCCUR ACROSS THE MOUNTAINS. THEREFORE, 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 NEAR TAU 72 AT A
DRASTICALLY WEAKENED STATE. GOING FORWARD, THE SYSTEM WILL WEAKEN
AT A SLOW AND GRADUAL PACE BUT LARGELY MAINTAIN TYPHOON STRENGTH
THROUGH THE MAJORITY OF THE FORECAST PERIOD. THE POSITION OF THE
SYSTEM AT TAU 120 IS FORECAST WITH INCREASING UNCERTAINY 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: NUMERICAL MODEL TRACK GUIDANCE IS IN TIGHT
AGREEMENT REGARDING THE TRACK FOR THE NEXT 36 TO 48 HOURS, THOUGH
VARYING SOMEWHAT IN TIMING. THE GFS TRACKER HAS SLOWED CONSIDERABLY
DURING THE TURN TO APPROACH TAIWAN AS COMPARED TO THE ECMWF TRACK
GUIDANCE WITH A TAU 48 SPREAD OF 70 NM. THE GFS TRACKER ALSO
DIVERGES AFTER LANDFALL AND PREDICTS A WESTWARD TURN ACROSS THE
TAIWAN STRAIT, WHICH GOES AGAINST THE GRAIN OF ALL OTHER CONSENSUS
MEMBER FORECASTS. EVEN THE LESS RELIABLE MODELS HAVE ASSEMBLED
CLOSE TO THE CONSENSUS MEAN, DEPICTING A GENERALLY NORTHEASTWARD
BISECTION ACROSS TAIWAN. LOOKING BEYOND TAU 120, THE ENSEMBLES
DIVERGE CONSIDERABLY. THE RANGE OF POSSIBLE SCENARIOS INCLUDE
BLOCKING TO THE NORTH, WHICH WILL DRIVE THE SYSTEM WEST INTO
MAINLAND CHINA, A RETREAT OF THE RIDGE, WHICH COULD OPEN UP A
PATHWAY TO THE NORTH OR NORTHEAST, OR UPPER-LEVEL ASSISTANCE IN THE
FORM OF A POLEWARD-VENTING MECHANISM THAT COULD ACT TO RESTRENGTHEN
THE SYSTEM. THE CURRENTLY DEPICTED INTENSITY GUIDANCE IS IN GOOD
AGREEMENT WITH A VERY GRADUAL DECLINE IN THE SYSTEM INTENSITY IN
THE NEAR TERM AND A SHARPER TREND DOWNWARDS UPON LANDFALL IN
TAWIAN. TOWARDS THE LATER TAUS, COAMPS-TC PREDICTS A SLIGHT
RESTRENGTHENING WILL OCCUR. TO ACCOUNT FOR THESE UNCERTAINTIES, THE
JTWC INTENSITY FORECAST IS HIGHER THAN THAT OF THE INTENSITY
CONSENSUS MEAN DUE TO SOME OUTLIERS DECAYING THE SYSTEM TOO
QUICKLY. 

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