WDPN31 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 09W (BAVI) WARNING NR 
016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.7N 149.6E
   INITIAL INTENSITY: 135 KTS
   GEOGRAPHIC REFERENCE: 295 NM EAST OF NAVSTA GUAM
   MOVEMENT PAST 6 HOURS: WESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
SYMMETRIC, HIGHLY ORGANIZED DEEP CONVECTIVE CANOPY EMBEDDING A
SHARPLY DEFINED EYE MEASURING 25 NM IN DIAMETER ASSOCIATED WITH
SUPER TYPHOON (STY) 09W (BAVI). THE INITIAL POSITION IS ESTABLISHED
WITH HIGH CONFIDENCE, BASED ON THE CLOUD-FREE, WARM (17 C) EYE
FEATURE. A CONSENSUS OF AGENCY SUBJECTIVE DVORAK ESTIMATES AND
OBJECTIVE SATELLITE-DERIVED INTENSITY ESTIMATES WERE USED TO ASSESS
THE INITIAL INTENSITY OF 135 KTS. A 041843Z F18 SSMIS 91 GHZ
MICROWAVE IMAGE REVEALS AN ESTABLISHED PRIMARY EYEWALL, HINTING AT
THE END OF A PARTIAL EYEWALL REPLACEMENT CYCLE (ERC), WHICH LED TO
A SLIGHT WEAKENING OF THE SYSTEM OVER THE LAST 6-12 HOURS. HOWEVER,
ENVIRONMENTAL ANALYSIS REVEALS A CONTINUOUSLY FAVORABLE ENVIRONMENT,
CHARACTERIZED BY VIGOROUS UPPER-LEVEL RADIAL OUTFLOW, MINIMAL
VERTICAL WIND SHEAR (VWS) OF 5-10 KTS, ABUNDANT DEEP-TROPOSPHERIC
MOISTURE, AND WARM SEA SURFACE TEMPERATURES (SST) OF 29-30 C.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: BUILDING EASTERN EXTENSION OF A
SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   RJTD: T7.0 - 140 KTS 
   RCTP: T7.0 - 140 KTS 
   KNES: T7.0 - 140 KTS 
   CIMSS SATCON: 142 KTS AT 041800Z
   CIMSS ADT: 132 KTS AT 041800Z
   CIMSS AIDT: 131 KTS AT 041800Z
   CIMSS D-MINT: 135 KTS AT 041544Z
   CIMSS D-PRINT: 136 KTS AT 041800Z

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

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: SYNOPTIC STEERING IS DOMINATED BY THE EASTERN
EXTENSION OF A SUBTROPICAL RIDGE (STR) ANCHORED NORTHEAST OF THE
SYSTEM, CAUSING THE CYCLONE TO MAINTAIN A SLOW WESTWARD
TRANSLATION. A PASSING MIDLATITUDE LONGWAVE TROUGH PROPAGATING TO
THE NORTH SPLITS THE BROAD STEERING RIDGE, RE-ORIENTING ITS
AXIS IMMEDIATELY POLEWARD OF STY 09W AND TEMPORARILY DECELERATING
THE CYCLONE FORWARD SPEED. ANALYSIS OF THE STORM MOTION HAS
REVEALED AN INTRODUCTION OF A WEST-NORTHWESTWARD TRACK VECTOR
COMPONENT. WHILE THE RIDGING TO THE NORTHEAST BUILDS, THE SYSTEM IS
EXPECTED TO START GAINING SPEED AS ITS TRACKING WEST-NORTHWESTWARD
AND TOWARDS THE MARIANA ISLANDS AND THROUGHOUT TAU 96. AFTERWARDS,
STY 09W IS EXPECTED TO START TURNING MORE POLEWARD ALONG THE
WEST-SOUTHWESTERN PERIPHERY OF THE STR CENTERED TO THE NORTHEAST.
GIVEN THE CURRENT TIMELINE, IT IS TOO EARLY TO SAY IF STY 09W WILL
BEGIN TO ROUND THE AXIS OF THE RIDGE AND TRACK FULLY POLEWARD AND
ALONG THE WESTERN PERIPHERY OF THE RIDGE, OR IF ITS TRACK WILL BE
CLOSER TO NORTHERN TAIWAN. IN TERMS OF INTENSITY, PEAK WIND SPEEDS
ARE FORECAST TO BRIEFLY PLATEAU, YET REACH 140 KTS BETWEEN TAU 24 AND 
TAU 48, PRIMARILY AS A RESULT OF AN OPENING ADDITIONAL OUTFLOW CHANNEL
TO THE WEST AND SOUTH. AROUND TAU 60, THE VWS WILL BEGIN TO
INCREASE, RESULTING IN A WEAKENING TREND. ULTIMATELY, BETWEEN
TAU 72 AND TAU 96, AN ESCALATION OF VWS TO 25-30 KTS WILL GRADUALLY
DEGRADE THE CORE CONVECTIVE STRUCTURE, HOWEVER THE SYSTEM IS
EXPECTED TO REMAIN A VERY STRONG TYPHOON, WITH AN EXPANSIVE WIND
FIELD REACHING AS FAR AS NORTHERN PHILIPPINES TO THE SOUTHWEST AND
OKINAWA TO THE NORTHEAST.

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE EXHIBITS GOOD
COHESION, PARTICULARLY THROUGH TAU 96 AND FEATURING A COMPACT
CROSS-TRACK SPREAD OF ONLY 40 NM DURING THE STY CLOSEST POINT OF
APPROACH (CPA) TO TINIAN AND ROTA ISLANDS. AS THE SYSTEM SLOWED
DOWN FOR LONGER THAN INITIALLY FORECAST, WHILE ONLY JUST TURNING
WEST-NORTHWESTWARD, THE CURRENT TRACK PREDICTION TAKES THE LLCC
MUCH CLOSER TO ROTA THAN TINIAN, SHIFTING THE TRACK 15 NM
SOUTHWEST, AS COMPARED TO THE FORECAST TRACK FROM 24 HOURS AGO. IN
TERMS OF THE LONG-TERM TRACK PREDICTION, NAVGEM IS THE ONLY OUTLIER
CURRENTLY PREDICTING A FAST RECURVATURE AND TRACK TOWARDS OKINAWA,
WHILE ALL OTHER GUIDANCE GENERATES A CONSENSUS VECTOR ORIENTED ON
NORTHERN TAIWAN. AS SUCH, JTWC TRACK FORECAST IS LAID WITH MEDIUM
CONFIDENCE FOR THE LONG TERM. IN REGARD TO INTENSITY, MESOSCALE
HIGH-RESOLUTION MODELS (HAFS AND COAMPS-TC) PROJECT SOME SLIGHT
INTENSIFICATION, REACHING AS HIGH AS 140-145 KTS PEAK INTENSITY,
LIKELY DRIVEN BY IMPROVING OUTFLOW. ALL OTHER MODEL GUIDANCE
INDICATES A SLOW AND GRADUAL WEAKENING, WITH SHORT PERIODS OF STY
09W MAINTAINING INTENSITY. JTWC OFFICIAL TRACK FORECAST IS LAID ON
THE HIGHER END OF THE MULTI-MODEL CONSENSUS AND REFLECTS SOME
POTENTIAL FOR MINOR INTENSIFICATION OVER THE NEXT 48 HOURS DUE TO
SLIGHT IMPROVEMENTS TO ALREADY FAVORABLE ENVIRONMENTAL CONDITIONS.

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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