Advisories

WDPN32 PGTW 050300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 26W (CHOI-WAN) WARNING NR 
021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.2N 146.5E
   INITIAL INTENSITY: 130 KTS
   GEOGRAPHIC REFERENCE: 284 NM EAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 46 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
WELL-DEFINED EYE WITHIN THE COMPACT CORE OF SUPER TYPHOON (STY) 26W
WHICH IS NEARLY SURROUNDED BY A MOAT OF SUPPRESSED CONVECTION
SEPARATING THE CORE FROM A LARGER BAND OF CONVECTION. THE COMPACT
CORE CONTINUES TO EXHIBIT A CYCLONIC PRECESSION WITHIN THE BROADER
CIRCULATION. THE SAME MOAT FEATURE IS PRESENT IN A 042127Z SSMIS 37
GHZ MICROWAVE IMAGE, WITH THE OUTER CONCENTRIC RING OF CONVECTION
STILL OPEN IN THE SOUTHWEST QUADRANT. THE 91 GHZ COUNTERPART OF THE
SAME MICROWAVE IMAGE SHOWS A SIMILAR STRUCTURE BUT IS LESS
WELL-DEFINED IN THE UPPER LEVELS. THE SATELLITE PRESENTATION AND
MICROWAVE IMAGERY SUGGEST THAT STY 26W MAY BE IN THE EARLY STAGE OF
ANOTHER EYEWALL REPLACEMENT CYCLE (ERC) ATTEMPT. A 042009Z RCM-1
SAR IMAGE REVEALED VERY SYMMETRIC STRONG WINDS IN THE COMPACT CORE
AND AN EXPANSIVE, THOUGH ASYMMETRIC, WIND FIELD THAT EXTENDS BEYOND
THE IMAGE FOOTPRINT. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE WELL-DEFINED EYE IN MSI. THE INITIAL
INTENSITY OF 130 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON
UNANIMOUS T6.5 AGENCY DVORAK FIXES AND THE 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: SAR AND SCATTEROMETER DATA SUPPLEMENTED
BY 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: T6.5 - 127 KTS
   RCTP: T6.5 - 127 KTS
   CIMSS SATCON: 128 KTS AT 050000Z
   CIMSS ADT: 117 KTS AT 050000Z
   CIMSS AIDT: 131 KTS AT 050000Z
   CIMSS D-MINT: 128 KTS AT 042126Z
   CIMSS D-PRINT: 114 KTS AT 050000Z

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

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: 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 AROUND
TAU 36 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. THE INTENSITY IS FORECAST TO STEADILY WEAKEN
THROUGHOUT THE FORECAST PERIOD AS THE SYSTEM CONTINUES POLEWARD
OVER COOLER SEA SURFACE TEMPERATURES AND LOWER OCEAN HEAT CONTENT.
THE POTENTIAL ATTEMPT AT AN ERC SHOULD ALSO BE A CONTRIBUTING
FACTOR AS THE OUTER RING OF CONVECTION COULD EFFECTIVELY CHOKE OFF
INFLOW TO THE COMPACT INNER CORE. IF ERC IS SOMEHOW SUCCESSFUL,
THERE COULD ALSO BE A SHORT REBOUND IN INTENSITY, THOUGH THAT
REMAINS UNLIKELY. 

MODEL DISCUSSION: MODEL TRACK GUIDANCE REMAINS IN GOOD AGREEMENT
THROUGHOUT THE FORECAST PERIOD WITH A CROSS-TRACK SPREAD AT TAU 60
OF 95 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 200 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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