WDPN32 PGTW 220900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (EIGHTEEN) 
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.9N 134.3E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 550 NM NORTH-NORTHWEST OF YAP
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS PERSISTENT
DEEP CONVECTION WRAPPING INTO A LOW LEVEL CIRCULATION CENTER (LLCC)
AS WELL AS EVIDENCED ON A 220552Z GMI 89GHZ MICROWAVE IMAGE. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
ANIMATED MULTISPECTRAL IMAGERY AND THE PREVIOUSLY MENTIONED
MICROWAVE IMAGERY. THE INITIAL INTENSITY IS PLACED WITH MEDIUM
CONFIDENCE BASED ON AN OLDER 220105Z METOP-C ASCAT AND A LATER
220413Z AMSR2 WINDSPEED IMAGE. THE ENVIRONMENTAL CONDITIONS ARE
FAVORABLE FOR GREATER DEVELOPMENT WITH MOSTLY WESTWARD OUTFLOW, LOW
VERTICAL WIND SHEAR, AND WARM (28-29C) SST VALUES.

INITIAL WIND RADII BASIS: PERSISTENCE

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.0 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 39 KTS AT 220650Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK WESTWARD

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: TS 18W REMAINS IN A QUASI-STATIONARY MOTION DUE 
TO A WEAK SYNOPTIC STEERING PATTERN WITH A COL DIRECTLY TO THE NORTH, 
IMPEDING ITS MOTION. THE DEEP-LAYER SUBTROPICAL RIDGE TO THE 
NORTHEAST WILL BEGIN TO BUILD AND BECOME THE DOMINATE STEERING 
FEATURE WITHIN THE NEXT 12 HOURS, FORCING TS 18W ON A WESTWARD JOG 
TOWARDS THE LUZON COAST OF THE PHILIPPINES. AS TS 18W TRANSITS OVER 
THE VERY WARM AND HIGH OCEAN HEAT CONTENT (OHC) OF THE PHILIPPINE 
SEA, IT WILL BEGIN TO INCREASE STEADILY WITH THE LACK OF VERTICAL 
WIND SHEAR, AND AN INCREASE OF POLEWARD OUTFLOW. THIS ENHANCED 
ENVIRONMENT WILL ALLOW THE SYSTEM TO INTENSIFY TO 55 KNOTS BY TAU 72. 
AFTER THE SYSTEM REACHES LUZON, IT WILL INITIALLY LOSE SOME INTENSITY 
OVER THE RUGGED TERRAIN BUT THEN REEMERGE OVER THE SOUTH CHINA SEA ON 
A CONTINUED WESTWARD TRACK. SHORTLY AFTER ENTERING THE SCS, TS 18W 
WILL STEADILY INTENSIFY TO TYPHOON STRENGTH NEAR HAINAN, CHINA, 
BETWEEN TAU 96 AND TAU 120.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL TIGHT AGREEMENT
WITH ONLY A 30NM SPREAD WITHOUT NAVGEM, THE SOLE LEFT OUTLIER. ADDING 
NAVGEM INDUCES A 158NM SPREAD THROUGH TAU 48 AND ONLY SPREADS. THE 
JTWC TRACK GUIDANCE LIES CLOSE TO ECMWF AND GFS THROUGH TAU 72 WITH 
HIGH CONFIDENCE. HOWEVER, ONCE THE SYSTEM MAKES LANDFALL OVER LUZON, 
THE CONFIDENCE WEAKENS GREATLY INDUCING TRACK SPREAD AND LOWERS THE 
TRACK CONFIDENCE THROUGH THE REMAINING FORECAST PERIOD. INTENSITY 
GUIDANCE INDICATES A HIGH SPREAD OF UNCERTAINLY. THEREFORE, THE JTWC 
INTENSITY FORECAST IS PLACED WITH LOW CONFIDENCE.

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