Advisories

WDPN32 PGTW 032100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 26W (CHOI-WAN) WARNING NR 016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.8N 146.7E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 340 NM NORTH OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 36 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A RAGGED
BUT INCREASINGLY PERSISTENT EYE SURROUNDED BY DEEP CONVECTION THAT
HAS IMPROVED IN SYMMETRY OVER THE PAST 6 HOURS. DEEP CONVECTION
AROUND THE COMPACT CORE HAS ALSO EXHIBITED GRADUALLY COOLING CLOUD
TOPS AS SYMMETRY IMPROVES. ANIMATED WATER VAPOR IMAGERY PRESENTS
IMPRESSIVE DUAL-CHANNEL OUTFLOW, WITH THE POLEWARD CHANNEL TAPPING
INTO A JET STREAK TO THE NORTH AND EQUATORWARD TRANSVERSE BANDING
EXTENDING NEARLY TO THE EQUATOR. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON THE EYE IN ANIMATED EIR. THE INITIAL
INTENSITY OF 95 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A
BLEND OF THE AGENCY DVORAK FIXES ON THE HIGHER END AND CIMSS
OBJECTIVE INTENSITY ESTIMATES ON THE LOWER END. 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 

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: T5.5 - 102 KTS
   RCTP: T5.0 - 90 KTS
   CIMSS SATCON: 87 KTS AT 031621Z
   CIMSS ADT: 67 KTS AT 031810Z
   CIMSS AIDT: 77 KTS AT 031810Z
   CIMSS D-MINT: 94 KTS AT 031622Z
   CIMSS D-PRINT: 94 KTS AT 031810Z

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 MEANDERED MORE
EASTWARD OVER THE PAST 6 HOURS, PARTLY FROM THE REMAINING EASTWARD
INFLUENCE OF THE NER TO THE SOUTH AND PARTLY AS AN ARTIFACT OF
TROCHOIDAL WOBBLE. THE NORTHWARD COMPONENT OF MOTION IS A RESULT OF
THE STR SITUATED TO THE NORTHEAST WHICH IS EXPECTED TO BECOME THE
DOMINANT STEERING MECHANISM OVER THE NEXT 48 HOURS. THE TRACK
FORECAST MAINTAINS A MEAN NORTHWARD TRAJECTORY THROUGH TAU 48,
THEN TURNS NORTHEASTWARD FROM TAU 48-72 AS THE SYSTEM ROUNDS THE
RIDGE AXIS. AFTER TAU 72, TY 26W APPROACHES AND BECOMES EMBEDDED IN
THE MID-LATITUDE WESTERLIES WHICH WILL RESULT IN AN ACCELERATED
TRACK SPEED TOWARD THE NORTHEAST. THE INTENSITY IS FORECAST TO
SHARPLY INCREASE OVER THE NEXT 12-18 HOURS IN A HIGHLY FAVORABLE
ENVIRONMENT, THEN PLATEAU AS EQUATORWARD OUTFLOW DECREASES AND IT
EXITS A REGION OF HIGH OCEAN HEAT CONTENT. GRADUAL WEAKENING IS
EXPECTED THROUGH TAU 60 OVER PROGRESSIVELY COOLER SEA SURFACE
TEMPERATURES. 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 80 NM AT TAU 72. ALONG-TRACK SPREAD AMONG
CONSENSUS MEMBERS INCREASES FROM 240 NM AT TAU 72 TO 330 NM AT TAU
96, EXCEPTING NAVGEM AS A MUCH SLOWER OUTLIER. THE SUITE OF
AI-BASED MODELS REMAIN OVERALL FASTER THAN THE BULK OF
PHYSICS-BASED CONSENSUS MODELS, BUT THE DISPARITY HAS DECREASED
SLIGHTLY WITH THE LATEST MODEL RUN. THE JTWC FORECAST IS PLACED
CLOSE TO THE MEAN OF ALL GUIDANCE THROUGHOUT THE FORECAST PERIOD.
IN TERMS OF INTENSITY, SEVERAL RAPID INTENSIFICATION (RI) AIDS
TRIGGERED THIS CYCLE, WHICH IS NO SURPRISE CONSIDERING THE CURRENT
ENVIRONMENT. THE REST OF THE INTENSITY GUIDANCE IS IN GOOD
AGREEMENT ABOUT THE OVERALL INTENSITY TREND AND FALLS WITHING AN
ENVELOPE OF ABOUT 20 KTS. THE JTWC FORECAST DEPICTS A SHARP
INCREASE IN INTENSITY OVER THE FIRST 12 HOURS TO ACCOUNT FOR THE
SHORT-TERM HIGHLY FAVORABLE ENVIRONMENT AND RI AIDS, BUT FALLS
SHORT OF DEPICTING RI BY DEFINITION. AFTER TAU 12, THE INTENSITY
FORECAST REMAINS ON THE HIGHER END OF THE GUIDANCE ENVELOPE TO
ACCOUNT FOR THE SHORT-TERM SPIKE.

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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