WDPN33 PGTW 280900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (KRATHON) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.5N 125.6E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 495 NM SOUTH-SOUTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED VISIBLE SATELLITE IMAGERY SHOWED A FULLY EXPOSED LOW LEVEL
CIRCULATION CENTER (LLCC) AT AROUND 280300Z, BUT THE LLCC HAS SINCE
BECOME TUCKED UNDER A PLUME OF DEEP CONVECTION. EXTENSIVE CYCLONIC
TURNING IS EVIDENT THROUGHOUT THE LOW LEVEL CLOUD LINES,
DEMONSTRATING THE BROAD EXTENT OF THE SYSTEM. MULTIPLE CONVECTIVE
BANDS ARE PULSING IN THE SOUTHERN SEMICIRCLE, SHEARED TO THE
SOUTHWEST WITH DIFFUSE OUTFLOW. THE PRESSURE ON THE NORTH SIDE IS
CURRENTLY LIMITING THE DEVELOPMENT. THE INITIAL POSITION IS PLACED
WITH MEDIUM CONFIDENCE BASED ON ANIMATED VISIBLE SATELLITE IMAGERY
AND SUPPORTED BY CURVED LOW-LEVEL BANDING ON A 280457Z AMSR2 37 GHZ
MICROWAVE IMAGE. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE DUE TO A LACK OF RECENT SCATTEROMETRY DATA, BUT
WITH GOOD AGREEMENT OF AGENCY SUBJECTIVE DVORAK ESTIMATES OF T2.5,
WHICH IS WELL WITHIN THE RANGE OF OBJECTIVE INTENSITY AIDS.

INITIAL WIND RADII BASIS: AMSR2 DATA

CURRENT STEERING MECHANISM: COMPETING STEERING BETWEEN SUBTROPICAL
RIDGES TO THE SOUTHWEST AND TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 33 KTS AT 280513Z
   CIMSS DPRINT: 37 KTS AT 280500Z
   CIMSS ADT: 37 KTS AT 280540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: THE SYSTEM HAS BEEN DRIFTING SLOWLY SOUTHWARD
IN A COL REGION BUT IS EXPECTED TO BECOME MORE HEAVILY INFLUENCED
BY THE SUBTROPICAL RIDGE TO THE NORTHEAST, WHICH WILL TURN ITS
TRACK WESTWARD AND SLOWLY CURVE IT NORTHWARD OVER THE NEXT FEW DAYS
WITH SPEEDS REMAINING CLIMATOLOGICALLY SLOW. THE TRACK IS EXPECTED
TO COME INTO CLOSE PROXIMITY WITH THE EAST COAST OF TAIWAN, BUT THE
DISTANCE REMAINS UNCERTAIN AT THIS TIME. DUE TO THE SLOW MOVEMENT
OF THE SYSTEM, THE SYSTEM IS EXPECTED TO HAVE AMPLE OPPORTUNITY TO
STRENGTHEN BETWEEN TAU 24 AND TAU 72 WHILE IT TREADS OVER WARM
WATERS AND EXPERIENCES FAVORABLE ENVIRONMENTAL CONDITIONS. AFTER
TAU 72, TS 20W WILL HAVE MOVED FAR ENOUGH NORTH TO BEGIN
INTERACTING WITH THE WESTERLIES ALOFT, WHICH WILL OPEN UP A
POLEWARD OUTFLOW CHANNEL IN ADDITION TO THE CONTINUED HEALTHY
EQUATORWARD OUTFLOW. HOWEVER, DEVELOPMENT WILL BECOME HAMPERED BY
THE LAND INTERACTION AS THE TRACK VENTURES CLOSE TO TAIWAN AND
EVENTUALLY THE VERTICAL WIND SHEAR WILL STRENGTHEN TO UNFAVORABLE
AMOUNTS.

MODEL DISCUSSION: GLOBAL DETERMINISTIC MODELS HAVE SHOWN POOR
AGREEMENT CONCERNING THE INITIAL DIRECTION OF MOVEMENT, WITH THE
ECMWF DEPICTING A MORE WESTWARD TRACK AND THE GFS TURNING THE
SYSTEM NORTH MUCH SOONER. HOWEVER, IT APPEARS THE ECMWF IS SHIFTING
THE TRACK CLOSER TO THE GFS GUIDANCE WITH EACH RUN. THE RELIABLE
TRACK GUIDANCE HAS A 260 NM SPREAD AT TAU 72, REFLECTING THE
UNCERTAINTIES IN THE STRENGTH OF THE RIDGE TO THE NORTHEAST TO ACT
AS THE STEERING MECHANISM. BECAUSE OF THE WIDE SWATH OF TRACK
PREDICTIONS, THE INTENSITY GUIDANCE INHERENTLY BECOMES LESS
CERTAIN. NUMERICAL GUIDANCE SUGGESTS A SLOW AND STEADY
STRENGTHENING UP TO A PEAK AT TAU 96, QUICKLY DROPPING OFF BY TAU
120. THE JTWC FORECAST IS PREDICTING A RAPID INTENSIFICATION PERIOD
TO OCCUR AFTER TAU 24 DUE TO THE DWELL TIME IN FAVORABLE
CONDITIONS, AN EARLIER PEAK NEAR TAU 72 DUE TO THE EXPECTED LAND
INTERACTION SOON AFTER. THE JTWC TRACK FORECAST IS PREDICTED WITH
LOW TO MEDIUM CONFIDENCE, HEDGED SLOWER THAN THE CONSENSUS MEAN BUT
IN CLOSER AGREEMENT TO THE MORE RELIABLE MODELS.

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