WDPN33 PGTW 170900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 23W (NESAT) WARNING NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.2N 116.4E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 223 NM SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 36 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TY 23W CONTINUES TO STRUGGLE TO MAINTAIN A CONSISTENT EYE FEATURE,
AT LEAST IN THE ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) AND
ENHANCED INFRARED (EIR). HOWEVER, IN THE MICROWAVE BANDS, THE EYE
FEATURE IS WELL DEFINED, AND THE SYSTEM CONTINUES TO INTENSIFY.
ANALYSIS OF 170136Z SCATTEROMETER AMBIGUITIES RESULTED IN A
SIGNIFICANT SOUTHEASTWARD ADJUSTMENT IN THE BEST TRACK POSITION. A
170548Z AMSR2 PASS CONFIRMED THIS ADJUSTMENT, SHOWING A WELL
DEFINED MICROWAVE EYE IN BOTH THE 89GHZ AND 36GHZ FREQUENCIES, WITH
ROUGHLY A 17NM DOWNSHEAR (TOWARDS THE NORTHWEST) TILT WITH HEIGHT,
PROVIDING HIGH CONFIDENCE TO THE INITIAL POSITION. THE INITIAL
INTENSITY IS ASSESSED WITH HIGH CONFIDENCE AT 90 KNOTS, ABOVE THE
BULK OF SUBJECTIVE AND OBJECTIVE DVORAK CURRENT INTENSITY ESTIMATES
DUE TO SEVERAL FACTORS INCLUDING; RAW ADT VALUES APPROACHING T5.5,
AN AIDT ESTIMATE OF 86 KNOTS, AN OPEN-AIIR ESTIMATE OF 95 KNOTS AND
AN AMSR2 WINDSPEED IMAGE SHOWING A LARGE REGION OF 90 PLUS KNOT
WINDS TO THE WEST OF THE CENTER, WITH A PEAK OF 103 KNOTS, TO THE
WEST OF THE CENTER. THE SYSTEM HAS SLOWED A BIT OVER THE PAST SIX
HOURS AS IT MOVES SOUTH OF A COL REGION AND IN A WEAKENED STEERING
FLOW. THE OVERALL ENVIRONMENT REMAINS FAVORABLE, WITH MODERATE
EASTERLY SHEAR, WARM SSTS AND MODERATE RADIAL OUTFLOW, THOUGH
RELATIVELY DRIER AIR EXTENDS IN A BAND TO THE SOUTH, WRAPPING UP TO
THE EASTERN PORTION OF THE CIRCULATION, INHIBITING CONVECTIVE
DEVELOPMENT THERE.

INITIAL WIND RADII BASIS: PERSISTENCE WITH EARLIER SCATTEROMETER
DATA AND AMSR2 WINDSPEED DATA.

CURRENT STEERING MECHANISM: RELATIVELY WEAK STEERING FLOW ALONG THE
SOUTH SIDE OF A COL REGION AND WEAKNESS IN THE STR TO THE NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.0 - 65 KTS
   KNES: T5.0 - 90 KTS
   CIMSS SATCON: 80 KTS AT 170539Z
   CIMSS ADT: 82 KTS AT 170540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: LOW-LEVEL DRY AIR INTRUSION TO THE SOUTH AND
EAST.  

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: THERE HAVE BEEN NO MAJOR CHANGES TO THE
FORECAST TRACK PHILOSOPHY OVER THE PAST SEVERAL FORECASTS, AND THE
STEERING PATTERN IS DEVELOPING AS EXPECTED. THE SYSTEM CURRENTLY
LIES SOUTH OF A WEAKNESS IN THE STEERING RIDGE TO THE NORTH AND
HENCE THE SYSTEM HAS SLOWED A BIT, BUT GENERALLY MAINTAINED THE
EXPECTED TRACK MOTION. TY 23W IS EXPECTED TO CONTINUE TRACKING
SOUTHWESTWARD OVER THE NEXT 36 HOURS, PICKING UP A BIT OF SPEED AS
THE STR BUILDS IN TO THE NORTH, AND STRENGTHENS THE STEERING
GRADIENT. AROUND TAU 36 THE STR WILL REPOSITION, DEVELOPING A NEW
CENTER OVER TAIWAN, WITH A SOUTHWEST PERIPHERY ORIENTED GENERALLY
NORTHWEST-SOUTHEAST. IN RESPONSE TO THIS SHIFT IN THE RIDGE, TY 23W
WILL TURN WEST, THEN WEST-NORTHWEST BY TAU 72. TY 23W HAS LIKELY
REACHED ITS PEAK INTENSITY, THOUGH IT REMAINS POSSIBLE IT COULD
BRIEFLY REACH 95 KNOTS IN THE NEXT SIX HOURS OR SO. SHEAR IS
EXPECTED TO INCREASE FAIRLY QUICKLY AFTER TAU 12, WHICH WILL RESULT
IN A STEADY WEAKENING TREND THROUGH TAU 72. AS THE SYSTEM SKIRTS
SOUTHERN HAINAN, DISRUPTION OF THE LOW-LEVEL FLOW, UPPER-LEVEL
CONVERGENCE AND SIGNIFICANT DRY AIR ENTRAINMENT FROM THE WEST AND
SOUTH WILL QUICKEN THE PACE OF WEAKENING. AS THE SYSTEM WEAKENS
SOUTH OF HAINAN, THE STEERING LEVEL WILL STEADILY LOWER, AND WITH
THE LOWER LEVEL WINDS BEING MORE EAST TO WEST, THE TRACK TRAJECTORY
WILL FLATTEN OUT A BIT THROUGH LANDFALL, WHICH IS EXPECTED NEAR TAU
96. ONCE ASHORE THE SYSTEM WILL RAPIDLY DISSIPATE BY THE END OF THE
FORECAST PERIOD OVER THE MOUNTAINOUS TERRAIN OF CENTRAL LAOS. 

MODEL DISCUSSION: MODEL SPREAD HAS INCREASED A FAIR AMOUNT WITH
THIS RUN, WITH NAVGEM MARKING THE NORTHERN AND THE UKMET MARKING
THE SOUTHERN EDGE OF AN ENVELOPE THAT REACHES 150NM AT TAU 48. THE
ENVELOPE ACTUALLY DECREASES IN SIZE AFTER TAU 72, BUT SEVERAL
TRACKERS INCLUDING THE GFS, GALWEM AND COAMPS-TC JUMP SHIP AFTER
TAU 96 AND SHOW THE SYSTEM MAKING A RUN FOR CAMBODIA. THESE
TRACKERS ARE HIGHLY SUSPECT AND DISCOUNTED FROM THE CONSENSUS AFTER
TAU 72. THE JTWC FORECAST LIES NORTH OF THE CONSENSUS MEAN, WHICH
IS BEING PULLED SOUTH BY THE UNREALISTIC MODELS MENTIONED ABOVE,
AND REMAINS GENERALLY CONSISTENT WITH THE PREVIOUS FORECASTS WITH
HIGH TO MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT
THAT THE SYSTEM HAS PEAKED, WITH ALL MODELS, SAVE FOR CTCX WHICH
SHOWS A SLIGHT INTENSIFICATION IN THE FIRST 12 HOURS, SEEING EYE TO
EYE ON THE OVERALL WEAKENING TREND, THOUGH THE MESOSCALE MODELS
SUGGEST THE SYSTEM WILL HOLD ONTO 90 KNOTS FOR THE NEXT 24 OR 36
HOURS. THE JTWC FORECAST IS ON THE HIGH SIDE OF THE GUIDANCE
PACKAGE BUT IN AGREEMENT ON THE GENERAL SHAPE OF THE CURVE. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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