WDPN32 PGTW 221500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (EIGHTEEN) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.0N 134.5E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 551 NM NORTH-NORTHWEST OF YAP
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS COMPACT
PERSISTENT DEEP CONVECTION WRAPPING INTO A LOW-LEVEL CIRCULATION
CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE
BASED ON THE LACK OF DATA WITH ONLY ANIMATED INFRARED IMAGERY.
THE INITIAL INTENSITY IS PLACED WITH LOW CONFIDENCE BASED ON
MULTIPLE AGENCY DVORAK ESTIMATES BETWEEN T1.5 AND T2.0. THE
ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE FOR ENHANCED DEVELOPMENT
WITH SLIGHT POLEWARD AND WESTWARD OUTFLOW, LOW TO MODERATE 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: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 43 KTS AT 221150Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: WEAK WESTWARD OUTFLOW

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: LOW
   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 CONTINUES TO REMAIN IN A
QUASI-STATIONARY STATUS DUE TO A WEAK SYNOPTIC STEERING PATTERN
WITH A COL DIRECTLY TO THE NORTH, WHICH IS CONTINUING TO IMPEDE ITS
MOTION. THE DEEP-LAYER SUBTROPICAL RIDGE TO THE NORTHEAST WILL
BEGIN TO BUILD AND BECOME THE DOMINANT STEERING FEATURE WITHIN THE
NEXT 6-12 HOURS. ONCE THE STR TAKES OVER STEERING IT WILL ALLOW FOR
TS 18W TO PROCEED ON A WESTWARD TRACK TOWARDS THE LUZON COAST OF
THE PHILIPPINES. DURING THE TRANSIT TS 18W WILL STEADILY INCREASE
INTENSITY TO A PEAK OF 60KTS AS IT PASSES OVER THE VERY WARM
PHILIPPINE SEA UNTIL IT MAKES ITS INITIAL LANDFALL ON THE NORTHERN
COAST OF LUZON. HOWEVER, THE SYSTEM WILL ONLY SLIGHTLY DECREASE IN
INTENSITY AFTER INTERACTING WITH THE RUGGED TERRAIN, AND THEN
REEMERGE OVER THE SOUTH CHINA SEA JUST AFTER TAU 48. TS 18W WILL
STEADILY INTENSIFY IN THE SOUTH CHINA SEA TO TYPHOON STRENGTH NEAR
HAINAN, CHINA, BETWEEN TAUS 96 AND 120 DUE TO ENHANCED OUTFLOW AND
LOW VERTICAL WIND SHEAR.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL TIGHT AGREEMENT
WITH ONLY A 30NM SPREAD EXCLUDING JGSM AND THE GFS ENSEMBLE, THE
SOLE LEFT OUTLIERS. KEEPING THOSE TO IN THE CONSENSUS INDUCES A
LARGER 140NM SPREAD THROUGH TAU 48 AND INCREASES TO 220NM BY TAU
96. THE JTWC TRACK GUIDANCE LIES CLOSE TO ECMWF AND GFS THROUGH TAU
72 WITH MEDIUM CONFIDENCE. HOWEVER, ONCE THE SYSTEM MOVES OVER
LUZON, THE CONFIDENCE WEAKENS GREATLY INDUCING ALONG TRACK AND
CROSS-TRACK SPREAD, LOWERING TRACK CONFIDENCE THROUGH THE REMAINING
FORECAST PERIOD. INTENSITY GUIDANCE INDICATES A HIGH SPREAD OF
UNCERTAINLY, AND THEREFORE, THE JTWC INTENSITY FORECAST IS PLACED
WITH LOW CONFIDENCE.

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