Advisories

WDPN32 PGTW 040300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 26W (CHOI-WAN) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.1N 147.1E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 358 NM EAST-SOUTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 38 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
WELL-DEFINED 20 NM DIAMETER EYE WITHIN A COMPACT CENTRAL CORE OF
VIGOROUS CONVECTION. A 032033Z GMI 89 GHZ MICROWAVE IMAGE AND ITS
37 GHZ COUNTERPART CONFIRMED THE STRUCTURAL INTEGRITY OF THE INNER
CORE AND VERTICAL ALIGNMENT OF THE VORTEX. DESPITE THE COMPACT
CORE, THE AREAL EXTENT OF TYPHOON 26W IS QUITE LARGE. ANIMATED
WATER VAPOR IMAGERY DEPICTS CONTINUED IMPRESSIVE DUAL-CHANNEL
OUTFLOW, WITH EQUATORWARD TRANSVERSE BANDING EXTENDING NEARLY TO
THE EQUATOR, ALTHOUGH THE POLEWARD CHANNEL HAS LOST SOME OF ITS
ENERGY. A 032002Z RCM-1 SAR PASS REVEALED A HIGHLY ASYMMETRIC WIND
FIELD BEYOND THE SYMMETRIC CORE, WITH THE STRONGEST WINDS EXTENDING
INTO THE EASTERN SEMICIRCLE AND AN 80 NM 64 KT WIND RADIUS IN THE
SOUTHEAST QUADRANT. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE WELL-DEFINED EYE IN ANIMATED MSI. THE
INITIAL INTENSITY OF 110 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE WIDE SPREAD OF AGENCY DVORAK FIXES AND CIMSS INTENSITY
ESTIMATES, BUT IS SUPPORTED BY A 110 KT MEAN VMAX FROM THE EARLIER
SAR IMAGE. THE ENVIRONMENT IS CHARACTERIZED AS HIGHLY FAVORABLE,
WITH VERY WARM SEA SURFACE TEMPERATURES, LOW VERTICAL WIND SHEAR
(VWS), EXCELLENT DUAL-CHANNEL OUTFLOW ALOFT, AND PLENTY OF
AVAILABLE MOISTURE.

INITIAL WIND RADII BASIS: PERSISTENCE SUPPLEMENTED BY PARTIAL
SCATTEROMETRY AND SAR PASSES

CURRENT STEERING MECHANISM: NORTHERN FLANK OF A NEAR EQUATORIAL
RIDGE (NER) TO THE SOUTH AND THE SOUTHWESTERN EXTENSION OF A
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T6.5 - 127 KTS
   CIMSS ADT: 82 KTS AT 032340Z
   CIMSS AIDT: 86 KTS AT 032340Z
   CIMSS D-MINT: 112 KTS AT 032023Z
   CIMSS D-PRINT: 118 KTS AT 040040Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG DUAL-CHANNEL

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: TYPHOON (TY) 26W (CHOI-WAN) HAS CONTINUED ON A
PRIMARILY NORTHWARD TRAJECTORY OVER THE PAST 6 HOURS, ALTHOUGH THE
INFLUENCE OF THE NER TO THE SOUTH HAS IMPARTED A SLIGHT EASTWARD
COMPONENT. TROCHOIDAL WOBBLE IS EVIDENT IN THE SEEMINGLY
INCONSISTENT ANALYSIS POSITIONS OVER THE PAST 24 HOURS BUT THE MEAN
TRACK OVER THIS PERIOD IS NORTH-NORTHEASTERLY. THE STR POSITIONED
TO THE NORTHEAST IS EXPECTED TO BECOME THE PRIMARY STEERING
MECHANISM OVER THE NEXT 36 HOURS, RESULTING IN A GENERALLY
NORTHWARD TRAJECTORY. AFTER TAU 36, TY 26W WILL ROUND THE RIDGE
AXIS AND SETTLE INTO A NORTHEASTWARD TRACK AROUND TAU 60. THE
SYSTEM APPROACHES AND BECOMES EMBEDDED IN THE MID-LATITUDE
WESTERLIES AFTER TAU 60, WHICH WILL RESULT IN AN ACCELERATED TRACK
SPEED TOWARD THE NORTHEAST. FOLLOWING A SPIKE IN INTENSITY OVER THE
PAST 6 HOURS, FROM 100 KTS TO 110 KTS, THE INTENSITY IS FORECAST TO
APPROACH A PEAK OF 120 KTS AT A MORE MODEST RATE AROUND TAU 12. THE
INTENSITY FORECAST THEN CALLS FOR GRADUAL WEAKENING OVER
PROGRESSIVELY COOLER SEA SURFACE TEMPERATURES AND THE INFLUENCE OF
DRY AIR ENTRAINMENT FROM THE WEST. TY 26W WILL APPROACH THE
ENTRANCE REGION OF A STRONG JET MAX BY TAU 72 AND BEGIN
EXTRATROPICAL TRANSITION IN THE ASSOCIATED BAROCLINIC ZONE, WITH
THE TRANSITION EXPECTED TO BE COMPLETE BY TAU 96.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT ABOUT
THE SHAPE OF THE TRACK THROUGHOUT THE FORECAST PERIOD, WITH A
CROSS-TRACK SPREAD OF 70 NM AT TAU 72, WHICH INCREASES BY TAU 96
LIKELY AS A RESULT OF THE FACT THAT THE SYSTEM WILL BE FULLY
EXTRATROPICAL BEFORE THEN. ALONG-TRACK SPREAD HAS CLOSED TO
200 NM WITH THE LATEST MODEL RUN, WITH THE EXCEPTION OF NAVGEM AS A
MUCH SLOWER OUTLIER. THE PHYSICS-BASED MODELS AND AI-BASED
SOLUTIONS HAVE ALSO COME INTO CLOSER AGREEMENT ABOUT THE TRACK
SPEED. THE JTWC TRACK FORECAST IS PLACED NEAR THE OVERALL MEAN OF
THE GUIDANCE SUITE THROUGHOUT THE FORECAST PERIOD. IN TERMS OF
INTENSITY, SEVERAL RAPID INTENSIFICATION (RI) AIDS TRIGGERED AGAIN
THIS CYCLE, WHICH CORROBORATES THE OBSERVED SPIKE IN INTENSITY OVER
THE PAST 6 HOURS. THE REST OF THE INTENSITY GUIDANCE IS IN GOOD
AGREEMENT ABOUT THE OVERALL INTENSITY TREND AND FALLS WITHIN AN
ENVELOPE OF ABOUT 20 KTS. THE JTWC FORECAST DEPICTS A MODERATELY
STEEP INCREASE FOR THE FIRST 12 HOURS GIVEN THE RECENT TREND, THEN
REMAINS ON THE HIGHER END OF THE GUIDANCE ENVELOPE TO ACCOUNT FOR
THE SHORT-TERM INTENSIFICATION.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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