WDPN32 PGTW 222100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (EIGHTEEN) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.1N 133.4E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 584 NM NORTH-NORTHWEST OF YAP
   MOVEMENT PAST 6 HOURS: WESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
COMPACT SYSTEM WITH PERSISTENT DEEP CONVECTION WRAPPING INTO A DEEP
CONVECTIVE CLOUD STRUCTURE OBSCURING A LOW LEVEL CIRCULATION CENTER
(LLCC). THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE
BASED ON A LACK OF SCATTEROMETRY DATA, THEREFORE THE SYSTEMS POSITION 
IS PLACED CLOSE TO AGENCY DVORAK FIXES. THE INITIAL INTENSITY IS
PLACED WITH MEDIUM CONFIDENCE BASED ON A COMBINATION OF SUBJECTIVE AND 
OBJECTIVE AGENCY DVORAK INTENSITY ESTIMATES, PGTW T2.5, KNES T2.5, 
RJTD 1.5, ALONG WITH ADT SHOWING UP TO 47 KTS AND AIDT SHOWING 42 KTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.5 - 35 KTS
   CIMSS ADT: 47 KTS AT 221430Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 IS CURRENTLY TRACKING WESTWARD AS THE
SYSTEM IS NOW UNDER THE INFLUENCE OF A DEEP-LAYER SUBTROPICAL RIDGE
TO THE NORTHEAST WHICH HAS TAKEN OVER AS THE DOMINATE STEERING
FEATURE. TS 18W WILL PROCEED ON A WESTWARD TRACK TOWARD THE COAST
OF LUZON OVER THE NEXT 48 HOURS. RAPID INTENSIFICATION GUIDANCE IS
TRIGGERED, ALTHOUGH BECAUSE THE SYSTEM WILL HAVE EASTERLY CONVERGENT 
FLOW ALOFT WITH OVERALL WEAK UPPER-LEVEL OUTFLOW, THE FORECAST WILL 
MAINTAIN A GRADUAL INTENSIFICATION UP TO 65 KNOTS THROUGH TAU 48. 
AFTER TAU 48, 18W IS FORECAST TO MAKE LANDFALL INTO LUZON, WHICH WILL 
LIKELY PUT A CAP ON INTENSIFICATION AND POSSIBLY DECREASE SLIGHTLY DUE 
TO THE SHORT PERIOD OF LAND INTERACTION. HOWEVER, BY TAU 72, THE 
SYSTEM MOVES BACK OVER THE WARM WATERS OF THE SOUTH CHINA SEA, AS THE 
UPPER LEVEL ENVIRONMENT BECOMES EVEN MORE FAVORABLE FOR 
INTENSIFICATION, CHARACTERIZED BY ENHANCED OUTFLOW AND LOW VERTICAL 
WIND SHEAR, THEREFORE THE OFFICIAL JTWC FORECAST SHOWS AN INCREASE UP 
TO 80 KNOTS BY TAU 96. BY TAU 120, 18W WILL CONTINUE A STRAIGHT 
RUNNING WESTWARD TRACK BEFORE EVENTUALLY MAKE LANDFALL INTO NORTHERN 
VIETNAM.  

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL TIGHT AGREEMENT
WITH THE EXCEPTION OF JGSM WHICH MAKES UP THE SOUTHERN OUTLIER,
WHILE NAVGEM IS THE NORTHERN OUTLIER. OVER THE NEXT 36 HOURS, TRACK
SPREAD WILL GRADUALLY INCREASE TO 97 NM BY TAU 48. AFTER THE SYSTEM
MOVES PAST LUZON AND BEYOND TAU 72, GUIDANCE BEGINS TO SPREAD EVEN
FURTHER TO A 235 NM CROSS-TRACK SPREAD, HOWEVER GUIDANCE REMAINS IN
OVERALL GOOD AGREEMENT REGARDING ALONG-TRACK SPREAD. INTENSITY
GUIDANCE INDICATES HIGH SPREAD OF UNCERTAINTY DUE TO RAPID
INTENSIFICATION GUIDANCE BEING TRIGGERED, 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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