WDPN32 PGTW 260300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W (NORU) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.9N 118.4E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 583 NM EAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TY 18W HAS WEAKENED SLIGHTLY, HOWEVER, THE SYSTEM IS WELL-ORGANIZED 
WITH IMPROVING POLEWARD OUTFLOW. ANIMATED ENHANCED INFRARED (EIR) 
SATELLITE IMAGERY SHOWS THE BULK OF THE SPIRAL BANDING OVER THE 
SOUTHERN SEMICIRCLE WITH FLARING DEEP CONVECTION OVER THE CENTER, 
HOWEVER, FRAGMENTED BANDING HAS RE-DEVELOPED OVER THE WESTERN 
QUADRANT. A 242226Z SSMIS 91GHZ MICROWAVE IMAGE DEPICTS TIGHTLY-
CURVED BANDING WRAPPING INTO A WELL-DEFINED LOW-LEVEL CIRCULATION 
CENTER, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE. THE 
INITIAL INTENSITY OF 75 KTS IS BASED PRIMARILY ON THE RJTD DVORAK 
INTENSITY ESTIMATE AND THE CIMSS ADT ESTIMATE. ENVIRONMENTAL 
CONDITIONS HAVE IMPROVED AS THE SYSTEM TRACKS AWAY FROM LUZON WITH 
MODERATE RADIAL OUTFLOW AND LOW VERTICAL WIND SHEAR.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) ENTRENCHED TO
THE NORTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   RJTD: T4.5 - 77 KTS
   KNES: T3.5 - 55 KTS
   CIMSS ADT: 74 KTS AT 252340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE 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: TY 18W IS FORECAST TO TRACK WESTWARD THROUGH
THE FORECAST PERIOD UNDER THE STEERING INFLUENCE OF THE STR 
POSITIONED TO THE NORTH, MAKING LANDFALL NEAR DA NANG, VIETNAM NEAR 
TAU 48. TY 18W IS FORECAST TO RAPIDLY INTENSIFY FROM TAU 24 TO TAU 48 
UNDER IMPROVING UPPER-LEVEL CONDITIONS TO A PEAK OF 110 KNOTS. AFTER 
TAU 48, THE SYSTEM WILL WEAKEN AS VERTICAL WIND SHEAR INCREASES AND 
THE SYSTEM TRACKS OVER SOUTHEAST ASIA WITH DISSIPATION EXPECTED BY 
TAU 96.   

MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM AFTER TAU 60, 
NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT LENDING HIGH 
CONFIDENCE TO THE JTWC FORECAST TRACK. THE OVERALL CONFIDENCE IN THE 
JTWC INTENSITY FORECAST IS MEDIUM DUE TO MODERATE UNCERTAINTY IN THE 
INITIAL INTENSITY AFTER THE SHORT TRANSIT ACROSS LUZON. THE BULK OF 
THE INTENSITY GUIDANCE INDICATES A RE-INTENSIFICATION PHASE WITH HWRF 
INDICATING A PEAK OF 115 KNOTS AT TAU 36 AND COAMPS-TC A PEAK OF 115-
120 KNOTS. THE 251800Z COAMPS-TC ENSEMBLE INDICATES A 20 TO 30 
PERCENT PROBABILITY OF RAPID INTENSIFICATION OVER THE NEXT 24 TO 48 
HOURS, GENERALLY SUPPORTING THE CURRENT FORECAST PHILOSOPHY.     

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