WDPN32 PGTW 180900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (MAN-YI) WARNING NR 
038//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.4N 116.8E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 276 NM SOUTH-SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAPIDLY
DETERIORATING SYSTEM, WITH A RAGGED LOW LEVEL CIRCULATION CENTER
(LLCC) PARTIALLY EXPOSED TO THE SOUTH OF FLARING DEEP CONVECTION. A
180529Z AMSR2 37GHZ MICROWAVE IMAGE REVEALED AN IRREGULAR,
BEAN-SHAPED LOW EMISSIVITY REGION (LER) AND SHALLOW BANDING
FEATURES TO THE SOUTH AND EAST AND STRONG, THOUGH DISORGANIZED,
CONVECTIVE ACTIVITY TO THE NORTH AND EAST. THE INITIAL POSITION IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE ANALYSIS OF THE
LOW-LEVEL CLOUD LINES EVIDENT TO THE SOUTH AND EAST OF THE LLCC IN
THE ANIMATED MSI AND EXTRAPOLATION OF THE LER IN THE AMSR2
MICROWAVE IMAGE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE DUE TO EXTREMELY LARGE SPREAD IN THE AVAILABLE
SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES. EARLY SAR DATA FROM
0030Z SHOWED MAXIMUM WINDS OF JUST 55 KNOTS IN THE NORTHEASTERN
QUADRANT, WHICH PROVIDED THE FIRST HINTS THAT THE BULK OF THE
AGENCY FIXES, AS WELL AS THE CIMSS ADT AND AIDT WERE SIGNIFICANTLY
HIGH. THE CIMSS DPRINT AND DMINT ALTERNATIVELY APPEAR TOO LOW. THE
INITIAL INTENSITY IS HELD AT 55 KNOTS, AT ROUGHLY THE MID-POINT OF
THE ESTIMATES NOTED ABOVE AND AS AN EXTRAPOLATION OF THE EARLIER
SAR DATA. THE ENVIRONMENT IS CURRENTLY UNFAVORABLE, WITH HIGH
SOUTHWESTERLY SHEAR, RELATIVELY COOL SSTS AND WEAK POLEWARD
OUTFLOW, MADE WORSE BY THE RAPID INFLUX OF DRY, RELATIVELY COOL AIR
FLOWING SOUTH OF THE TAIWAN STRAIT AND INTO THE WESTERN SIDE OF THE
SYSTEM.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN SIDE OF AN EXTENSION OF THE
SUBTROPICAL RIDGE (STR) EXTENDING FROM NORTHERN VIETNAM, ACROSS
TAIWAN AND INTO THE PHILIPPINE SEA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T5.0 - 90 KTS
   CIMSS ADT: 74 KTS AT 180530Z
   CIMSS AIDT: 64 KTS AT 180530Z
   CIMSS D-MINT: 34 KTS AT 180529Z
   CIMSS D-PRINT: 34 KTS AT 180600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: DRY, RELATIVELY COOL MID-LEVEL AIR FLOWING
SOUTHWARD THROUGH THE TAIWAN STRAIT. 

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: TROPICAL STORM (TS) 25W (MAN-YI) HAS STARTED
ITS TURN TO THE WEST BASED ON THE MOST RECENT ANALYSIS, MAYBE A
SHADE EARLIER THAN EXPECTED. A GENERAL WESTWARD TRACK IS FORECAST
FOR THE NEXT 12 TO 24 HOURS, AS THE SYSTEM TRACKS ALONG THE
SOUTHERN EDGE OF AN EXTENSION OF THE STR POSITIONED TO THE NORTH.
SHEAR HAS ALREADY INCREASED SHARPLY, JUST IN THE LAST SIX HOURS OR
SO, AND THIS TREND IS EXPECTED TO CONTINUE FOR THE NEXT 12 TO 24
HOURS. THE GFS AND ECMWF MODEL SOUNDINGS SUGGESTS DEEP-LAYER SHEAR
COULD EXCEED 30 KNOTS BY TAU 12. AT THE SAME TIME, THE SYSTEM WILL
BE SMOTHERED BY DRY AIR WHICH WILL BE USHERED IN ON THE BACK OF THE
STRONG SHEAR. THE VORTEX WILL SHALLOW OUT RAPIDLY AFTER TAU 24, AND
QUICKLY AND STEADILY WEAKEN THROUGH THE REMAINDER OF THE FORECAST
PERIOD. THE REMNANT LOW-LEVEL VORTEX WILL TURN TOWARDS THE
SOUTHWEST AFTER TAU 24, MOVING ALONG THE LOW-LEVEL FLOW LINES,
SKIRT THE SOUTHERN COAST OF HAINAN AND THEN MOVE ONWARD TOWARDS THE
COAST OF VIETNAM BY TAU 72. THE SYSTEM IS CURRENTLY FORECAST TO
DISSIPATE BELOW WARNING CRITERIA AT TAU 72, BUT IN REALITY, IT WILL
LIKELY FULLY DISSIPATE WELL BEFORE THAT, POTENTIALLY AS EARLY AS
TAU 48.

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN MARGINAL
AGREEMENT THROUGH THE FORECAST PERIOD. ECWMF, EGRR AND JGSM
CONTINUE TO TAKE THE SYSTEM ON A WESTWARD COURSE THROUGH TAU 48,
WHERE IT LOSES THE VORTEX OVER HAINAN ISLAND. THE GFS AND GEFS MEAN
FOLLOW THE CONSENSUS THROUGH ABOUT TAU 48, THEN TURN NORTHWESTWARD
INTO THE SOUTHERN PORTION OF THE GULF OF TONKIN. THE REMAINDER OF
THE CONSENSUS MEMBERS AND THE MEAN ITSELF TRACK THE SYSTEM INTO
VIETNAM NEAR HUE. THE JTWC FORECAST LIES CLOSE TO THE CONSENSUS
MEAN, WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD
AGREEMENT THAT THE SYSTEM WILL STEADILY WEAKEN THROUGH THE FORECAST
PERIOD, WITH SOME MODELS SUGGESTING AN EARLIER DISSIPATION NEAR TAU
48. THE JTWC FORECAST LIES CLOSE TO THE HAFS-A INTENSITY TREND,
WITH MEDIUM CONFIDENCE.  

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