WDPN32 PGTW 230900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 24W (RAGASA) WARNING NR 020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.4N 117.1E
   INITIAL INTENSITY: 120 KTS
   GEOGRAPHIC REFERENCE: 198 NM SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
WELL-DEFINED 25 NM EYE WITH A SLIGHTLY ASYMMETRIC CENTRAL DENSE
OVERCAST OVER THE EYEWALL. THE BULK OF THE COLDEST CLOUD TOPS ARE
NOW CONFINED TO THE SOUTHERN SEMICIRCLE RATHER THAN EVENLY
DISPLACED AROUND THE EYE. ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY REVEALS WEAKENING IN THE NORTHWESTERN QUADRANT
AND WARMING CLOUD TOPS OVER THE PAST 6 HOURS. ENVIRONMENTAL
ANALYSIS INDICATES A HIGHLY FAVORABLE ENVIRONMENT, CHARACTERIZED BY
STRONG RADIAL OUTFLOW, WARM SEA SURFACE TEMPERATURES (28-29 C), AND
LOW VERTICAL WIND SHEAR (10-15 KTS). THERE IS A STREAK OF DRY AIR
TO THE NORTHWEST OF THE SYSTEM, HOWEVER, IT APPEARS TO HAVE LITTLE
EFFECT ON THE INTENSITY. THE INITIAL INTENSITY OF 120 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE VISIBLE WEAKENING OF
THE NORTHWESTERN QUADRANT IN THE AFOREMENTIONED ANIMATED EIR,
CORROBORATED BY THE OBJECTIVE INTENSITY AIDS AND AGENCY DVORAK
FIXES LISTED BELOW. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE DEFINED EYE.

INITIAL WIND RADII BASIS: PERSISTENCE WITH ADJUSTMENTS BASED ON THE
PARTIAL 230200Z METOP-B ASCAT PASS

CURRENT STEERING MECHANISM: THE ELONGATED SOUTHERN PERIPHERY OF THE
SUBTROPICAL RIDGE (STR) TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T6.5 - 127 KTS
   RCTP: T7.0 - 140 KTS 
   KNES: T6.0 - 115 KTS
   DEMS: T6.5 - 127 KTS
   CIMSS SATCON: 137 KTS AT 230513Z
   CIMSS ADT: 127 KTS AT 230540Z
   CIMSS AIDT: 120 KTS AT 230540Z
   CIMSS D-MINT: 118 KTS AT 230513Z
   CIMSS D-PRINT: 124 KTS AT 230630Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TYPHOON (TY) 24W IS FORECAST TO MAINTAIN ITS
WEST-NORTHWESTWARD TRACK UNTIL LANDFALL NEAR YANGJIANG, CHINA JUST
AFTER TAU 24. AFTER WHICH, 24W IS EXPECTED TO TAKE A MORE WESTWARD
TRAJECTORY AS THE STR TO ITS NORTH BUILDS. A TRACK JUST NORTH OF
THE GULF OF TONKIN IS FORECAST FROM TAU 36-48. 24W WILL THEN TRACK
INTO NORTHERN VIETNAM AND LAOS NEAR THE END OF THE FORECAST PERIOD.
REGARDING INTENSITY, 24W WILL ENTER INTO A REGION OF MODERATE SHEAR
(15-20 KTS) OVER THE NEXT 24 HOURS, CONTRIBUTING TO ITS WEAKENING
PRIOR TO LANDFALL. ONCE 24W IS OVER LAND, TERRAIN INTERACTION WILL
RAPIDLY DEGRADE THE SYSTEM, LEADING TO DISSIPATION NO LATER THAN
TAU 72.

MODEL DISCUSSION: JTWC NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGH THE FORECAST PERIOD, HOWEVER THERE IS SOME SLIGHT
DISAGREEMENT OVER WHETHER 24W WILL REEMERGE OVER THE GULF OF
TONKIN OR REMAIN OVER LAND. UKMET, JGSM AND ECMWF ARE AMONG THE
JTWC CONSENSUS MEMBERS THAT KEEP 24W OVER LAND, WHILE GFS AND NAVGEM
PREDICT 24W REEMERGING. THE JTWC TRACK FORECAST HEDGES TOWARDS THE
FORMER MEMBERS, HOLDING 24W OVER LAND UNTIL DISSIPATION. AS A
RESULT, THE JTWC TRACK FORECAST IS PLACED WITH MEDIUM CONFIDENCE.
RELIABLE INTENSITY GUIDANCE IS IN STRONG AGREEMENT ON A STEADY
WEAKENING TREND THROUGH DISSIPATION, LENDING HIGH CONFIDENCE TO THE
JTWC INTENSITY FORECAST.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   INTENSITY 00-72 HR: HIGH//
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