WDPN32 PGTW 252100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W (NORU) WARNING NR 016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.6N 119.8E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 664 NM EAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TY 18W WEAKENED SIGNIFICANTLY AS IT TRACKED OVER CENTRAL LUZON,
HOWEVER, ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY
INDICATES DEEP CONVECTIVE BANDING IS IMPROVING AND WRAPPING INTO
THE SOUTHEAST QUADRANT OF THE LOW-LEVEL CIRCULATION CENTER (LLCC),
WHICH IS POSITIONED JUST OFF THE WESTERN COAST OF LUZON. THE
SYSTEM'S CENTER IS CURRENTLY LOCATED ABOUT 15-20NM NORTHWEST OF IBA
(98324), WHICH REPORTED A MINIMUM SLP VALUE OF 994.5MB AT 251700Z.
THE SURFACE WINDS ARE BACKING AND ARE CURRENTLY SOUTHWESTERLY AT 29 
KNOTS. A 251734Z ATMS 88.2GHZ MICROWAVE IMAGE REVEALS CURVED BANDING 
OVER THE SOUTHERN SEMICIRCLE WITH WEAK STRUCTURE ELSEWHERE. THE 
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE ATMS 
IMAGE AND SURFACE OBSERVATIONS. THE INITIAL INTENSITY OF 90 KTS IS 
ASSESSED WITH LOW CONFIDENCE CONSERVATIVELY BASED ON THE DVORAK 
INTENSITY ESTIMATES, HOWEVER, THE CONVECTIVE STRUCTURE SUGGESTS A 
LOWER INTENSITY. ENVIRONMENTAL CONDITIONS HAVE DEGRADED WITH 
INCREASING UPPER-LEVEL EASTERLIES AND WEAK POLEWARD OUTFLOW OFFSET BY 
MODERATE EQUATORWARD 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: T6.0 - 115 KTS
   RJTD: T5.0 - 90 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: FRICTIONAL EFFECTS DUE TO PROXIMITY TO LAND

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 60. TY 18W IS FORECAST TO RAPIDLY INTENSIFY FROM TAU 24 TO TAU
48 UNDER IMPROVING UPPER-LEVEL CONDITIONS TO A PEAK OF 105 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 AND AFUM 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 SIGNIFICANT
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 93 KNOTS AT
TAU 48 AND COAMPS-TC A PEAK OF 110 KNOTS. THE PEAK INTENSITY IS
DIFFICULT TO ACCURATELY PINPOINT SINCE IT WILL DEPEND ON THE
UNCERTAIN INITIAL INTENSITY AND ANY ADDITIONAL WEAKENING OVER THE
NEXT 12 HOURS. THE 251200Z COAMPS-TC ENSEMBLE INDICATES A 20 TO 30
PERCENT PROBABILITY OF RAPID INTENSIFICATION, 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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