WDPN31 PGTW 081500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (CONSON) WARNING NR 
011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.7N 120.1E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 53 NM WEST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
AFTER HAVING MAINTAINED INTENSITY WHILE CROSSING OVER THE SMALLER
PHILIPPINE ISLANDS AND THE SIBUYAN SEA, TS 18W HAS FINALLY
SUCCUMBED TO THE INFLUENCE OF TERRAIN AND HAS WEAKENED A BIT SINCE
THE PREVIOUS FIX. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY DEPICTS WELL DEFINED SPIRAL BANDS WRAPPING INTO A DIFFUSE
AND DISORGANIZED LOW LEVEL CIRCULATION CENTER (LLCC). THE LACK OF
RECENT MICROWAVE IMAGERY, AND THE LACK OF RADAR COVERAGE OVER THE
MANILA BAY REGION RESULTED IN A DEGRADATION IN THE TRACK CONFIDENCE
OVER THE PAST SIX HOURS. THE LLCC APPEARS TO BE EMERGING BACK INTO
RADAR COVERAGE, JUST OFFSHORE OF SUBIC BAY, BUT IT LOOKS MUCH MORE
RAGGED AND DIFFUSE, THUS THERE IS ONLY MEDIUM CONFIDENCE IN THE
INITIAL POSITION. THE INITIAL INTENSITY IS SET AT 50 KNOTS,
SLIGHTLY HIGHER THAN THE AVERAGE OF SUBJECTIVE AND OBJECTIVE DVORAK
ESTIMATES, WITH MEDIUM CONFIDENCE. ENVIRONMENTAL CONDITIONS REMAIN
FAVORABLE WITH LOW VWS, RADIAL OUTFLOW WITH A WEAK POLEWARD OUTFLOW
CHANNEL DEVELOPING AND WARM SSTS. THE ONLY LIMITING FACTOR AT THE
CURRENT TIME IS PROXIMITY TO LAND, LEADING TO DISRUPTION OF THE LOW
LEVEL CIRCULATION.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   KNES: T4.0 - 65 KTS
   CIMSS ADT: 51 KTS AT 081140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK RADIAL
   OTHER FACTORS: DEVELOPING POLEWARD OUTFLOW CHANNEL. 

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 FORECAST TO CONTINUE TRACKING
WEST-NORTHWEST ALONG THE SOUTHWEST SIDE OF THE DEEP STR CENTERED TO
THE NORTHEAST THROUGH THE NEXT 12 HOURS. AFTER TAU 24 THE RIDGE IS
EXPECTED TO BUILD TOWARDS THE WEST ALONG A LINE FROM THE NORTHERN
RYUKUS TO SOUTH-CENTRAL CHINA. THIS CHANGE IN THE STEERING PATTERN
WILL TURN TS 18W ONTO A MORE WESTWARD TRACK AFTER TAU 24. THE
LATEST GFS AND ECMWF ENSEMBLE RUNS ARE BOTH FORECASTING A STRONG
STR CENTER TO DEVELOP OVER SOUTHERN CHINA AFTER TAU 36, RESULTING
IN A FLATTER, MORE WESTWARD TRACK FOR TS 18W. ALL ENSEMBLE MEMBERS
FOR GFS AND THE MAJORITY OF THE ECMWF MEMBERS KEEP THE TRACK SOUTH
OF HAINAN. STY 19W IS CURRENTLY LOCATED APPROXIMATELY 600NM EAST OF
TS 18W AND IS EXPECTED TO CLOSE WITHIN APPROXIMATELY 450NM, INSIDE
THE RANGE WHEN BINARY INTERACTION COULD BE ANTICIPATED. HOWEVER,
DUE TO THE SMALL SIZE OF BOTH SYSTEMS, BINARY INTERACTION IS NOT
EXPECTED AT THIS TIME. WHILE THE SYSTEM IS BACK OVER WATER, THE
LINGERING EFFECTS OF TERRAIN INTERACTION WILL LIMIT INTENSIFICATION
FOR THE NEXT 12 HOURS. AFTER TAU 12 THE SYSTEM IS FORECAST TO
STEADILY INTENSIFY UNDER FAVORABLE ENVIRONMENTAL CONDITIONS TO A
PEAK OF 70 KNOTS AT TAU 72. INCREASING VWS AND DECREASING SSTS AND
OHC VALUES WILL SERVE TO OFFSET STRONG WESTWARD OUTFLOW, LEADING TO
A SLOW WEAKENING TREND THROUGH THE REMAINDER OF THE FORECAST
PERIOD. 

MODEL DISCUSSION: NAVGEM AND GALWEM CONTINUE TO DISPLAY ANOMALOUS
BEHAVIOR, SHOWING A DRASTIC TURN NORTHEAST BY TAU 24, THEN BECOMING
ABSORBED BY STY 19W. THUS THESE MODELS ARE DISCOUNTED AND NOT
INCLUDED IN THE CONSENSUS TRACK CALCULATIONS. THE REMAINDER OF THE
GUIDANCE IS IN FAIR AGREEMENT OVERALL. THE NOTABLE EXCEPTION IS THE
GFS AND HWRF, WHICH SHOW A SIGNIFICANT SLOWDOWN AND TURN
SOUTHWESTWARD AFTER TAU 72, TAKING THE SYSTEM ASHORE JUST SOUTH OF
DA NANG, VIETNAM. THE BULK OF THE REMAINING GUIDANCE, INCLUDING THE
ECMWF, ECMWF ENSEMBLE, UKMET AND UKMET ENSEMBLE AND THE GFS
ENSEMBLE, IS TIGHTLY PACKED INDICATING WESTWARD TRACK THROUGH TAU
96 AND A SLIGHT TURN POLEWARD BY TAU 120. THE JTWC FORECAST IS
FLATTER THAN THE PREVIOUS FORECAST, AND SOUTH OF THE ADJUSTED
CONSENSUS MEAN, CLOSELY TRACKING THE GFS ENSEMBLE MEAN. THERE IS
OVERALL HIGH CONFIDENCE THROUGH TAU 72, AND LOW CONFIDENCE
THEREAFTER. INTENSITY GUIDANCE IS IN OVERALL GOOD AGREEMENT, WITH
THE EXCEPTION OF GFS WHICH DISSIPATES THE SYSTEM BY TAU 72. THE
REMAINDER OF THE GUIDANCE SUPPORTS STEADY STATE IN THE NEAR-TERM
FOLLOWED BY SLOW AND STEADY INTENSIFICATION TO TAU 72, THEN STEADY
WEAKENING. THE JTWC FORECAST IS SLIGHTLY ABOVE THE CONSENSUS MEAN
WITH MEDIUM CONFIDENCE FOR THE DURATION OF THE FORECAST PERIOD.   

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