WDPN31 PGTW 072100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (CONSON) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.3N 122.0E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 97 NM SOUTHEAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TS 18W HAS MAINTAINED INTENSITY WHILE TRACKING OVER THE SIBUYAN SEA
WITH NO SIGNIFICANT DEGRADATION OVER THE PAST SIX HOURS. ANIMATED
ENHANCED INFRARED (EIR) SATELLITE IMAGERY, RADAR IMAGERY AND A
071742Z AMSR2 89GHZ IMAGE DEPICT TIGHTLY-CURVED BANDING WRAPPING
INTO A WELL-DEFINED LOW-LEVEL CIRCULATION CENTER, WHICH SUPPORTS
THE INITIAL POSITION WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF
55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE PGTW DVORAK
ESTIMATE, CONSISTENT WITH THE OVERALL CONVECTIVE STRUCTURE AND
MICROWAVE EYE FEATURE. UPPER-LEVEL ANALYSIS INDICATES FAVORABLE
OUTFLOW CONDITIONS WITH THE EXCEPTION OF SOME INTERACTION WITH
LAND.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   CIMSS ADT: 55 KTS AT 071740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: INTERACTION WITH LAND 

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 IS FORECAST TO WEAKEN SLIGHTLY TO 45
KNOTS AS IT TRACKS NORTHWESTWARD OVER SOUTHERN LUZON. AFTER TAU 36,
THE SYSTEM WILL GRADUALLY STRENGTHEN OVER THE SOUTH CHINA SEA AS IT
TRACKS WESTWARD TO WEST-NORTHWESTWARD TOWARD HAINAN ISLAND. THERE
IS A LOW PROBABILITY THAT WEAK INTERACTION AND POSSIBLY MINOR
TRACK CHANGES MAY OCCUR AFTER TAU 48 AS TS 18W CLOSES WITHIN ABOUT
500NM OF TY 19W AT TAU 60.   

MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM, WHICH IS INDICATING
BINARY INTERACTION WITH TY 19W AND TRACKING QUICKLY POLEWARD AND
MERGING, NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT THROUGH TAU
72. THEREFORE, THERE IS MEDIUM CONFIDENCE IN THE JTWC FORECAST
TRACK THROUGH TAU 72. AFTER TAU 72, THE NUMERICAL MODELS DIVERGE
WITH A LARGE SPREAD IN SOLUTIONS RANGING FROM A WESTWARD TRACK TO A
NORTHWARD TRACK JUST EAST OF HAINAN ISLAND LENDING LOW CONFIDENCE
TO THE JTWC FORECAST TRACK IN THE EXTENDED PERIOD. THERE IS ALSO
SIGNIFICANT UNCERTAINTY IN THE JTWC INTENSITY FORECAST IN THE EARLY
PERIOD DUE TO LAND INTERACTION, AND IN THE LATER PERIOD DUE TO
INCREASING VERTICAL WIND SHEAR. AS A SIDE NOTE, THE 061200Z BEST
TRACK POSITION WAS REANALYZED TO TYPHOON STRENGTH (65 KNOTS) BASED
ON SURFACE OBSERVATIONS FROM GUIUAN, PHILIPPINES. THE 061300Z
REPORT INDICATED WEST-SOUTHWESTERLY WINDS AT 62 KNOTS AT AN
ELEVATION OF 60M.    

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