WDPN31 PGTW 171500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (RAI) WARNING NR 019//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.4N 117.8E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 297 NM SOUTH-SOUTHWEST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A BROAD
AREA OF CONVECTION MOVED OVER THE ISLAND OF PALAWAN AND ENTERED THE
SOUTH CHINA SEA. THE CONVECTIVE MASS IS NOW MORE ORGANIZED AND
SURROUNDS THE MAIN LLCC AS INDICATED BY AN EARLIER 171040Z SSMIS
91GHZ MICROWAVE EYE FEATURE, LENDING TO MEDIUM CONFIDENCE IN THE
INITIAL POSITION. THE INITIAL INTENSITY IS SET WITH MEDIUM
CONFIDENCE AND HEDGED SLIGHTLY HIGHER THAN ADT AT 70KTS, SATCON 
77KTS, AND IS HOLDING WITH THE VAST MAJORITY OF DVORAK CURRENT 
INTENSITY ESTIMATES LYING BETWEEN T4.5(77KTS) AND T5.5(102KTS) SHOWN 
BELOW. ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE, WITH WARM SSTS, 
MODERATE EASTERLY SHEAR, GOOD WESTWARD, AND SLIGHT POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE NORTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T4.5 - 77 KTS
   KNES: T5.0 - 90 KTS
   CIMSS SATCON: 77 KTS AT 171240Z
   CIMSS ADT: 70 KTS AT 171240Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE WESTWARD
   OTHER FACTORS: FAIR POLEWARD OUTFLOW

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: TY 28W HAS CONTINUALLY DEGRADED OVER THE PAST
SEVERAL HOURS, BUT IS NOW MOVING AWAY FROM PALAWAN ISLAND AND IS
NOW OVER THE WARM WATERS OF THE SOUTH CHINA SEA. AS THE SYSTEM
MOVES WEST IT WILL BEGIN TO DEEPEN AND INTENSIFY DUE TO AN
UPPER-LEVEL ANTICYCLONE THAT IS EXPECTED TO FORM OVER THE SYSTEM,
REDUCING BOTH THE VWS AND INCREASE THE AVAILABLE OUTFLOW. THE
INCREASED OUTFLOW AND WARM SSTS WILL HELP THE SYSTEM REACH A PEAK
OF 105 KNOTS BY TAU 24. THEREAFTER, THE SYSTEM WILL THEN GRADUALLY
TURN MORE NORTHWESTWARD WITH EACH PASSING HOUR AND BY TAU 48, IT
WILL TURN SHARPLY POLEWARD AS IT ROUNDS THE STR AS THE RIDGE
RETREATS EASTWARD. SHORTLY AFTER TAU 48, THE SYSTEM WILL ENCOUNTER
COOLER SSTS AND BEGIN TO WEAKEN RAPIDLY AS THE SURGE FROM THE
NORTHEAST WILL INCREASE VWS AND EXPOSE THE LOW-LEVEL CIRCULATION.
THE SYSTEM WILL FULLY DISSIPATE OVER THE WATER BY TAU 120, TURNING
EAST-SOUTHEASTWARD FOLLOWING THE LOW-LEVEL FLOW PATTERN SOUTHEAST
OF HONG KONG. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD AGREEMENT THROUGH
TAU 72, WITH A MODEST SPREAD OF ONLY 165NM AT THIS TIME. AS THE
SYSTEM RECURVES THE GUIDANCE SPREADS BUT REMAINS IN RELATIVELY GOOD
AGREEMENT WITH THE SPREAD, ONLY INCREASING 20NM AT TAU 96, THEN
DRASTICALLY BIFURCATES TO 315NM AT TAU 120. THE BULK OF THE
GUIDANCE IS CONSTRAINED WITHIN A TIGHT ENVELOPE THROUGH THE
FORECAST PERIOD. HOWEVER, WITH GALWEM REMAINING THE LEFT OUTLIER
BRINGING THE SYSTEM JUST SOUTH OF HONG KONG AND GFS TURNING THE
SYSTEM SHARPLY INTO THE CENTRAL SOUTH CHINA SEA. THE JTWC FORECAST
LIES ALONG THE NORTHERN SIDE OF THE ENVELOPE THROUGH TAU 48, THEN
ON THE INSIDE OF THE RECURVE TRACK THROUGH TAU 120. CONFIDENCE IS
HIGH THROUGH TAU 72, THEN LOW THEREAFTER AS THE RATE OF WEAKENING
WILL HAVE A LARGE IMPACT ON THE ULTIMATE TRACK. INTENSITY GUIDANCE
IS IN AGREEMENT WITH THE OVERALL INTENSIFICATION AND WEAKENING
TREND BUT DEPICTS FAIRLY LARGE DIFFERENCES IN THE ACTUAL 
INTENSITIES. THE JTWC FORECAST CLOSELY TRACKS THE HWRF THROUGH TAU
48 AND THEN FALLS MORE IN LINE WITH THE CONSENSUS MEAN THROUGH THE
REMAINDER OF THE FORECAST. UNCERTAINTY REMAINS HIGH THROUGH THE
FORECAST, AS THE ULTIMATE INTENSITY RELIES UPON HOW QUICKLY THE
SYSTEM WILL INTENSIFY IN THE SOUTH CHINA SEA. THUS THERE IS LOW
CONFIDENCE IN THE JTWC INTENSITY FORECAST.  

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