Advisories

WDPN32 PGTW 051500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 26W (CHOI-WAN) WARNING NR 023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.3N 145.9E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 290 NM EAST-NORTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 44 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
26W (CHOI-WAN) WITH A STEADILY DEGRADING STRUCTURE. CLOUD TOPS HAVE
CONTINUED TO WARM OVER THE PAST 6 HOURS AND THE CENTRAL DENSE
OVERCAST HAS STARTED TO BECOME IRREGULAR, PARTICULARLY IN THE
WESTERN SEMICIRCLE. THE DRY SLOT THAT WAS EVIDENT 6 HOURS AGO HAS
NOW ENTIRELY ENCIRCLED THE INNER-CORE. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE INCREASINGLY RAGGED EYE IN
ANIMATED EIR IMAGERY. THE INITIAL INTENSITY OF 110 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK AND CIMSS
INTENSITY ESTIMATES LISTED BELOW. ENVIRONMENTAL ANALYSIS INDICATES
THAT 26W IS NOW IN A MARGINAL ENVIRONMENT CHARACTERIZED BY STRONG
POLEWARD OUTFLOW ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND
WARM (28-29 C) SEA SURFACE TEMPERATURES GREATLY OFFSET BY
SIGNIFICANT DRY AIR ENTRAINMENT.

INITIAL WIND RADII BASIS: PERSISTENCE WITH SLIGHT ADJUSTMENTS BASED
ON THE OBJECTIVE BEST TRACK

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T5.5 - 102 KTS
   RCTP: T5.5 - 102 KTS
   CIMSS ADT: 104 KTS AT 051200Z
   CIMSS AIDT: 112 KTS AT 051200Z
   CIMSS D-MINT: 107 KTS AT 051214Z
   CIMSS D-PRINT: 113 KTS AT 051200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR ENTRAINMENT

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

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 12. NEAR TAU 12, 26W WILL APPROACH THE STEERING
RIDGE AXIS AND BEGIN TURNING NORTHEASTWARD. TRACK SPEEDS WILL
SIGNIFICANTLY INCREASE STARTING AROUND TAU 24 AS AN INCOMING
LONGWAVE TROUGH PICKS UP 26W AND USHERS IT QUICKLY NORTHEASTWARD.
EXTRATROPICAL TRANSITION IS FORECAST TO BEGIN AT TAU 36 AND
COMPLETE AT TAU 48 AS THE SYSTEM BECOMES EMBEDDED UNDERNEATH THE 
JET SOUTH OF THE KAMCHATKA PENINSULA. REGARDING INTENSITY, 26W IS 
FORECAST TO STEADILY WEAKEN THROUGH TAU 36 DUE TO DRY AIR ENTRAINMENT 
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 SHORT FORECAST PERIOD WITH THE SOLE EXCEPTION OF NAVGEM, WHICH 
IS SIGNIFICANTLY SLOWER. CROSS-TRACK SPREAD IS MEASURED TO BE ABOUT 
140 NM AT TAU 48 WHILE ALONG-TRACK SPREAD IS 200 NM (DISCOUNTING 
NAVGEM). THE JTWC TRACK FORECAST IS PLACED NEAR THE MODIFIED MULTI-
MODEL CONSENSUS WITH HIGH CONFIDENCE. INTENSITY GUIDANCE AGREES ON A 
STEADY WEAKENING TREND 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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