WDPN32 PGTW 050900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 26W (CHOI-WAN) WARNING NR 022//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.3N 146.3E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 285 NM EAST-NORTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON 26W
(CHOI-WAN) WITH A DEGRADING APPEARANCE INDICATED BY WARMING CLOUD
TOPS,  A THINNING CENTRAL DENSE OVERCAST, AND A COOLING EYE. THERE
IS ALSO A PROMINENT DRY SLOT FORMING TO THE IMMEDIATE NORTH OF THE
INNER-CORE. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON THE EYE IN ANIMATED MSI. THE INITIAL INTENSITY OF 115 KTS
IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES
AND CIMSS INTENSITY ESTIMATES LISTED BELOW. THE PGTW DATA-T NUMBERS
HAVE BEEN CONSISTENTLY T5.5 AS WELL, CLEARLY INDICATING A WEAKENING
TREND. ENVIRONMENTAL ANALYSIS INDICATES THAT 26W IS NOW IN A
MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD
OUTFLOW ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND WARM (28-29
C) SEA SURFACE TEMPERATURES OFFSET BY THE DRY AIR ENTRAINMENT FROM
THE WEST.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: THE WESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T6.5 - 127 KTS
   CIMSS SATCON: 127 KTS AT 050600Z
   CIMSS ADT: 112 KTS AT 050600Z
   CIMSS AIDT: 126 KTS AT 050530Z
   CIMSS D-MINT: 114 KTS AT 050317Z
   CIMSS D-PRINT: 116 KTS AT 050600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE WEST

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 26W IS FORECAST TO CONTINUE TRACKING
GENERALLY NORTHWARD, ALONG THE WESTERN PERIPHERY OF THE STR TO THE
EAST THROUGH TAU 24. NEAR TAU 24, 26W WILL APPROACH THE STEERING
RIDGE AXIS AND BEGIN TURNING NORTHEASTWARD. TRACK SPEEDS WILL
SIGNIFICANTLY INCREASE STARTING AROUND TAU 36 AS AN INCOMING
LONGWAVE TROUGH PICKS UP 26W AND USHERS IT QUICKLY NORTHEASTWARD.
EXTRATROPICAL TRANSITION IS FORECAST TO BEGIN AT TAU 48 AND
COMPLETE NO LATER THAN TAU 60 AS THE SYSTEM BECOMES EMBEDDED
UNDERNEATH THE JET SOUTH OF THE KAMCHATKA PENINSULA. REGARDING
INTENSITY, 26W IS FORECAST TO STEADILY WEAKEN THOUGH TAU 36 DUE TO
DRY AIR AND COOLING SEA SURFACE TEMPERATURES. FOLLOWING TAU 36,
WESTERLY SHEAR WILL DRASTICALLY INCREASE, CAUSING THE SYSTEM TO
FURTHER WEAKEN. HOWEVER, 26W WILL TAP INTO AN EXTREME POLEWARD
OUTFLOW CHANNEL, SUPPORTED BY A VERY STRONG JET MAX TO THE NORTH.
THIS WILL ALLOW FOR THE SYSTEM TO MAINTAIN AN INTENSITY NEAR
TYPHOON STRENGTH AS IT UNDERGOES EXTRATROPICAL TRANSITION AND
BECOMES A POTENT COLD-CORE LOW. 

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT
THROUGHOUT THE FORECAST PERIOD WITH NO NOTABLE OUTLIERS PRESENT.
THE ALONG-TRACK SPREAD HAS SIGNIFICANTLY IMPROVED COMPARED TO 6-12
HOURS AGO. CROSS-TRACK SPREAD IS MEASURED TO BE ABOUT 200 NM AT TAU
60. THE JTWC TRACK FORECAST IS PLACED NEAR THE MULTI-MODEL
CONSENSUS WITH HIGH CONFIDENCE. INTENSITY GUIDANCE AGREES ON STEADY
WEAKENING THROUGHOUT THE FORECAST PERIOD. AS A RESULT, THE JTWC
INTENSITY FORECAST IS ALSO PLACED NEAR THE CONSENSUS WITH HIGH
CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: HIGH//
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