WDPN34 PGTW 150300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (USAGI) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.5N 120.2E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 125 NM SOUTH OF KAOHSIUNG, TAIWAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 34 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM HAS
SLIGHTLY STRENGTHENED DUE TO DIURNAL COOLING AS EVIDENCED BY
OVERSHOOTING CLOUD TOPS IN THE CENTRAL DENSE OVERCAST. TRANSVERSE
BANDING IS EVIDENT ALONG THE NORTHERN RIM, AN INDICATION OF HIGH
SHEAR. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
A DEFINED
LOW LEVEL CIRCULATION CENTER IN A COMPOSITE RADAR LOOP FROM THE
TAIWAN CENTRAL WEATHER BUREAU. THE INITIAL INTENSITY OF 70KTS IS
ALSO 
PLACED WITH HIGH CONFIDENCE BASED ON OVERALL ASSESSMENT OF AGENCY
AND AUTOMATED DVORAK ESTIMATES AND REFLECTS THE SLIGHT 6-HR
INTENSIFICATION IN THE CONVECTIVE STRUCTURE. ANALYSIS INDICATES A
MARGINAL ENVIRONMENT WITH COOL (26-27C) SST, MODERATE TO STRONG
VWS, AND MODERATE RADIAL OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE.

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO
THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.0 - 65 KTS
   KNES: T4.5 - 77 KTS
   CIMSS ADT: 87 KTS AT 142330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TY USAGI WILL TRACK NORTHWARD AND ARC TO THE
RIGHT AS IT ROUNDS THE WESTERN PERIPHERY OF THE STEERING STR AND
MAKE LANDFALL NEAR KAOHSIUNG AROUND TAU 24. AFTERWARD, A SECONDARY
STR BUILDING IN FROM THE WEST NEAR HAINAN WILL COMPETE FOR STEERING
AND SLOW DOWN THE STORM MOTION, RENDERING THE CYCLONE IN A
QUASI-STATIONARY MODE IN THE COL AREA BETWEEN THE TWO STRS AND OVER
THE RUGGED SOUTHEASTERN MOUNTAIN RIDGES OF TAIWAN. COOL SSTS,
INCREASING VWS, THEN LAND INTERACTION WITH THE RUGGED TERRAIN OF
TAIWAN WILL SLOWLY THEN RAPIDLY ERODE THE SYSTEM TO DISSIPATION BY
TAU 48, LIKELY SOONER.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIRLY GOOD AGREEMENT UP
TO TAU 24; AFTERWARD, A FEW MODELS TRACK THE VORTEX NORTHEASTWARD
AND THE REST SOUTHWESTWARD IN RESPONSE TO THE SECONDARY STR, LENDING 
OVERALL MEDIUM CONFIDENCE TO THE JTWC TRACK AND INTENSITY FORECASTS 
THAT ARE LAID CLOSE TO THE MODEL CONSENSUS. 

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