Advisories

WDPN32 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 26W (CHOI-WAN) WARNING NR 
020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.4N 147.1E
   INITIAL INTENSITY: 135 KTS
   GEOGRAPHIC REFERENCE: 317 NM EAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 47 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A VERY
WARM AND WELL-DEFINED EYE SURROUNDED BY A SYMMETRIC CENTRAL DENSE
OVERCAST WHICH HAS EXHIBITED A CYCLONIC PRECESSION WITHIN THE
BROADER CIRCULATION ASSOCIATED WITH SUPER TYPHOON (STY) 26W. A
041517Z AMSR-3 37 GHZ MICROWAVE IMAGE SHOWS THE COMPACT CORE OF THE
VORTEX SURROUNDED BY A NEARLY CLOSED CONCENTRIC RING OF DEEP
CONVECTION. EARLIER MICROWAVE IMAGERY DEPICTED A MORE COMPLETE
OUTER RING, SUGGESTING THAT A POTENTIAL ATTEMPT AT AN EYEWALL
REPLACEMENT CYCLE HAS FAILED TO GAIN TRACTION. POLEWARD OUTFLOW IN
ANIMATED WATER VAPOR IMAGERY REMAINS ROBUST AS IT TAPS INTO A
STRONG JET MAX TO THE NORTH. THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE BASED ON THE WELL-DEFINED EYE IN EIR. THE INITIAL
INTENSITY OF 135 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A
BLEND OF THE AGENCY DVORAK FIXES AND CIMSS OBJECTIVE INTENSITY
ESTIMATES. THE ENVIRONMENT IS CHARACTERIZED AS FAVORABLE, WITH WARM
SEA SURFACE TEMPERATURES, LOW VERTICAL WIND SHEAR (VWS), AND STRONG
POLEWARD OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   RJTD: T6.5 - 127 KTS
   CIMSS SATCON: 134 KTS AT 041602Z
   CIMSS ADT: 132 KTS AT 041800Z
   CIMSS AIDT: 131 KTS AT 041800Z
   CIMSS D-MINT: 134 KTS AT 041603Z
   CIMSS D-PRINT: 137 KTS AT 041800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

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: STY 26W IS FORECAST TO TRACK GENERALLY
NORTHWARD ALONG THE WESTERN PERIPHERY OF THE STR TO THE EAST OVER
THE NEXT 24 HOURS, THEN TAKE ON A NORTHEASTWARD TRAJECTORY BY TAU 48
AS IT ROUNDS THE RIDGE AXIS. TRACK SPEED BEGINS TO ACCELERATE
AROUND TAU 36 AS THE SYSTEM APPROACHES THE MIDLATITUDE WESTERLIES
AND A LONGWAVE TROUGH TRANSITING EASTWARD OVER HONSHU. A STRONG JET
MAX PROPAGATING ALONG THE JET STREAM IS EXPECTED TO ENHANCE
POLEWARD OUTFLOW AS STY 26W TRACKS INTO THE BAROCLINIC ZONE. THE
BAROCLINIC FORCING SHOULD ALLOW THE SYSTEM TO MAINTAIN TYPHOON
INTENSITY THROUGH TAU 60 WHILE SIMULTANEOUSLY INITIATING
EXTRATROPICAL TRANSITION (ETT) SOMETIME BETWEEN TAU 48-60. ETT IS
EXPECTED TO BE COMPLETE BY TAU 72 AS THE VORTEX BECOMES EMBEDDED
UNDERNEATH THE JET. IT APPEARS THAT STY 26W REACHED ITS PEAK
INTENSITY OF 140 KTS OVER 6 HOURS AGO AND HAS SINCE WEAKENED
GRADUALLY IN AN ENVIRONMENT THAT REMAINS FAVORABLE. STEADY
WEAKENING IS FORECAST THROUGHOUT THE FORECAST PERIOD AS THE SYSTEM
CONTINUES POLEWARD OVER COOLER SEA SURFACE TEMPERATURES AND LOWER
OCEAN HEAT CONTENT. 

MODEL DISCUSSION: MODEL TRACK GUIDANCE REMAINS IN GOOD AGREEMENT
THROUGHOUT THE FORECAST PERIOD WITH A CROSS-TRACK SPREAD AT TAU 60
OF 100 NM. THE SPREAD INCREASES AFTER TAU 60, LIKELY AS A RESULT OF
THE ETT PROCESS AND ASSOCIATED DEFORMATION OF THE VORTEX. THE
ALONG-TRACK SPREAD AT TAU 72 IS ABOUT 270 NM, EXCLUDING NAVGEM AS A
MUCH SLOWER OUTLIER. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE
CONSENSUS MEAN THROUGHOUT THE FORECAST PERIOD, WITH A SLIGHT BIAS
TOWARD THE FASTER AI GUIDANCE. THE INTENSITY AIDS ARE IN GOOD
AGREEMENT ABOUT THE WEAKENING TREND BUT WITH SOME UNCERTAINTY ABOUT
THE RATE OF WEAKENING. THE JTWC INTENSITY FORECAST IS PLACED CLOSE
TO THE CONSENSUS, WHICH REMAINS ON THE HIGHER END OF GUIDANCE
THROUGH THE FIRST 36 HOURS.

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