WDPN31 PGTW 081500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 24W (YINXING) WARNING NR 022//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.4N 116.9E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 279 NM SOUTH-SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THAT THE
CONVECTIVE STRUCTURE OF TYPHOON (TY) 24W (YINXING) SIGNIFICANTLY
ERODED OVER THE PAST SIX HOURS, BUT IN THE LAST HOUR HAS STARTED TO
RECOVER. AT ANALYSIS TIME, THE SYSTEM DISPLAYED A COMMA HEAD TYPE
STRUCTURE, WITH A WEDGE OF DRY AIR INTRUDING DOWN THE WEST SIDE OF
THE CIRCULATION AND WRAPPING IN TOWARDS THE CORE. THROUGH 1400Z
HOWEVER, CONVECTIVE ACTIVITY HAS BEEN ABLE TO OVERCOME THIS DRY AIR
INTRUSION AND REDEVELOP A RAGGED CDO. THE EYE HAS BECOME MORE
RAGGED OVER THE PAST COUPLE OF HOURS AS THE REMNANT DRY AIR LOOKS
TO HAVE PENETRATED IN TOWARDS THE CENTER. THE INITIAL POSITION WAS
ASSESSED WITH HIGH CONFIDENCE BASED ON A 19NM WIDE EYE IN THE EIR
AND EXTRAPOLATION OF A WELL-DEFINED MICROWAVE EYE IN A 0955Z SSMIS
COLOR-ENHANCED 89GHZ IMAGE. THE INITIAL INTENSITY WAS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE SUBJECTIVE AND OBJECTIVE INTENSITY
ESTIMATES NOTED ABOVE. A 1016Z RCM-1 SAR PASS THAT WAS RECEIVED
AFTER ANALYSIS TIME SHOWS A PEAK WIND OF 86 KNOTS, SO THE INITIAL
INTENSITY MAY BE 5 KNOTS TOO HIGH. THE ENVIRONMENT IS MARGINALLY
FAVORABLE, WITH LOW SOUTHEASTERLY WIND SHEAR AND WARM SSTS, OFFSET
BY THE INTRUSION OF DRY AIR AND REDUCED UPPER-LEVEL OUTFLOW AS THE
SYSTEM BECOMES ISOLATED FROM THE POLEWARD OUTFLOW CHANNEL.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) EXTENDING FROM HAINAN ISLAND, THROUGH TAIWAN AND INTO A
STR CENTER EAST OF OKINAWA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T6.0 - 115 KTS
   KNES: T5.0 - 90 KTS
   DEMS: T5.5 - 102 KTS
   CIMSS SATCON: 91 KTS AT 080952Z
   CIMSS ADT: 104 KTS AT 081130Z
   CIMSS AIDT: 91 KTS AT 081200Z
   CIMSS D-MINT: 88 KTS AT 080955Z
   CIMSS D-PRINT: 85 KTS AT 081230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: DRY MID-LEVEL AIR STARTING TO IMPINGE ON THE
WESTERN SIDE OF THE CIRCULATION. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TYPHOON 24W WILL CONTINUE TO TRACK
WEST-NORTHWESTWARD OVER THE NEXT 24 HOURS, ALONG THE SOUTHERN SIDE
OF THE STEERING RIDGE TO THE NORTH. HOWEVER, TRACK SPEEDS WILL
BEGIN TO SLOW DOWN AFTER TAU 12 DUE A WEAKENING STEERING GRADIENT.
AN UNSEASONABLY STRONG UPPER-LEVEL TROF CURRENTLY PASSING NORTH OF
VIETNAM, WILL SOON MOVE INTO EASTERN CHINA, AND BREAK THE RIDGE IN
THE VICINITY OF HONG KONG. THE BREAK IN THE RIDGE WILL RESULT IN A
WEAK STEERING PATTERN, AND TY 24W WILL LAY ON THE BRAKES AFTER TAU
24 AS IT MEANDERS FOR A TIME TO THE SOUTH OF HONG KONG. TY 24W HAS
ABOUT 24 HOURS LEFT OF RELATIVELY FAVORABLE CONDITIONS, THOUGH
CYCLING DRY AIR INTRUSIONS WILL PRECLUDE MUCH IN THE WAY OF
INTENSIFICATION. THE FORECAST CALLS FOR 5 KNOTS OF INTENSIFICATION
THROUGH TAU 24 BUT THE SYSTEM MAY FLUCTUATE BOTH ABOVE AND BELOW
THE 90 KNOT THRESHOLD DURING THIS TIME. BY TAU 36, INCREASING
SOUTHERLY SHEAR AND UPWELLING OF COOLER OCEAN WATERS WILL BEGIN TO
TAKE THEIR TOLL, AND THE SYSTEM WILL BEGIN TO WEAKEN AS IT
CONTINUES TO STAGNATE EAST OF HAINAN. BY TAU 48, IT WILL BE LIGHTS
OUT AS SHEAR INCREASES TO OVER 30 KNOTS AND DRY AIR COMPLETELY
ENGULFS THE SYSTEM FROM THE SOUTHWEST, DECAPITATING THE VORTEX
ABOVE ABOUT 700MB. AS THE SYSTEM TURNS SOUTHWESTWARD ALONG THE EAST
SIDE OF A RIDGE THAT DEVELOPS OVER LAOS, IT WILL CONTINUE WEAKEN
RAPIDLY AND STEADILY. VEXED BY DRY AIR AND CONTINUED HIGH SHEAR,
THE SYSTEM IS FORECAST TO DISSIPATE ALONG THE COAST OF CENTRAL
VIETNAM BY TAU 96. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE CONTINUES TO BE IN
VERY GOOD AGREEMENT FOR THE FIRST 48 HOURS OF THE FORECAST, WITH
LITTLE IN THE WAY OF CROSS- OR ALONG-TRACK UNCERTAINTY, LENDING
HIGH CONFIDENCE TO THE SHORT-TERM FORECAST. AFTER THE SYSTEM TURNS
SOUTHWARD (AFTER TAU 48), THE GUIDANCE BEGINS TO DIVERGE
DRAMATICALLY, AS THE MODELS DISAGREE ON THE ORIENTATION AND
STRENGTH OF THE LOW- TO MID-LEVEL STEERING FLOW. THE ECMWF AND JGSM
TAKE THE SYSTEM ON A MORE WEST-SOUTHWESTWARD TRACK, SKIRTING THE
COAST OF HAINAN AND HEADING INLAND NEAR HUE, VIETNAM. THE GFS
MEANWHILE TAKES A MORE SOUTHWARD TRACK, REMAINING WELL OFFSHORE OF
SOUTHERN VIETNAM BY THE END OF THE FORECAST PERIOD. THE GAP BETWEEN
THE TWO OUTLIERS REACHES 310NM BY TAU 96, LENDING MEDIUM CONFIDENCE
TO THE JTWC FORECAST WHICH REMAINS CLOSE TO THE CONSENSUS MEAN.
INTENSITY GUIDANCE IS IN STRONG AGREEMENT, WITH THE HAFS-A, HWRF
AND CONSENSUS MEAN ALL FLUCTUATING TIGHTLY BETWEEN 90-95 KNOTS
THROUGH TAU 24, THEN DROPPING SHARPLY THROUGH THE REMAINDER OF THE
FORECAST. THE JTWC FORECAST TRACES THE TIGHTLY GROUPED MODELS NOTED
ABOVE THROUGH THE FORECAST PERIOD, WITH HIGH CONFIDENCE.  

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