WDPN31 PGTW 201500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (FENGSHEN) WARNING 
NR 
011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.5N 114.2E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 228 NM SOUTH OF HONG KONG
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A RATHER
DISORGANIZED APPEARANCE, AS TROPICAL STORM (TS) 30W CONTINUES TO
STRUGGLE TO ORGANIZE AND INTENSIFY. OVER THE PAST SIX HOURS,
CONVECTIVE ACTIVITY HAS WEAKENED AND BECOME MORE FRAGMENTED, THOUGH
IN THE LAST HOUR OR TWO, DEEP CONVECTION HAS BEGUN TO REFORM NEAR
THE CENTER BUT REMAINS DISORGANIZED. A 201006Z WSF-M COLOR-ENHANCED
89GHZ IMAGE REVEALED FRAGMENTARY CONVECTIVE BANDS WRAPPING INTO AN
ILL-DEFINED LOW LEVEL CIRCULATION CENTER (LLCC). THE STRONGEST
CONVECTION REMAINS POSITIONED TO THE EAST AND NORTHEAST OF THE
LLCC, DUE TO PERSISTENT MODERATE SOUTHERLY SHEAR. SHIP OBSERVATIONS
EAST OF HONG KONG INDICATE VERY STRONG NORTH-EASTERLY FLOW IS
PUSHING SOUTHWESTWARD TO THE WEST OF TS 30W, WITH ANIMATED EIR
SUGGESTING THESE STRONG WINDS EXTEND ALL THE WAY TO HAINAN.
ANIMATED WATER VAPOR IMAGERY SHOWS STRONG POLEWARD OUTFLOW AND
MODERATE EQUATORWARD OUTFLOW ALOFT. THE INITIAL POSITION IS
ASSESSED WITH HIGH CONFIDENCE BASED ON ANALYSIS OF THE WSF-M
MICROWAVE IMAGE NOTED ABOVE. THE INITIAL INTENSITY IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON A BLEND OF THE OBJECTIVE AND SUBJECTIVE
INTENSITY ESTIMATES NOTED BELOW. THE ENVIRONMENT IS ABOUT AS GOOD
AS IT'S GOING TO BE RIGHT NOW, WITH STRONG POLEWARD OUTFLOW, WARM
SSTS, A POOL OF RELATIVELY HIGH OHC RIGHT ALONG THE TRACK, AND LOW
SOUTHERLY SHEAR.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF THE WESTERN
EXTENSION OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) THAT EXTENDS FROM
NORTHERN VIETNAM, ACROSS SOUTHERN CHINA, TO A POSITION EAST OF
OKINAWA.  

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T3.5 - 55 KTS
   DEMS: T3.0 - 45 KTS
   CIMSS ADT: 39 KTS AT 201130Z
   CIMSS AIDT: 37 KTS AT 201130Z
   CIMSS D-MINT: 37 KTS AT 200757Z
   CIMSS D-PRINT: 41 KTS AT 201200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: MODERATE EQUATORWARD OUTFLOW. INTERACTION WITH
COLD SURGE FLOW TRAPPED ALONG THE CHINESE COAST. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST HAS BEEN TRUNCATED TO 72
HOURS. 

FORECAST DISCUSSION: THE TRACK OF TS 30W HAS ALREADY FLATTENED OUT
AND THE SYSTEM IS NOW TRACKING DUE WEST, ALONG THE SOUTHERN SIDE OF
AN EXTENSION OF THE STR POSITIONED OVER SOUTHEASTERN CHINA. THE
SYSTEM IS FORECAST TO CONTINUE TRACKING WESTWARD FOR THE NEXT 12
HOURS, BEFORE MAKING A SHARP SOUTHWESTWARD TURN AS IT COMES UNDER
THE STEERING INFLUENCE OF A BUILDING RIDGE OVER NORTHERN VIETNAM.
ADDITIONAL SUPPORT FOR THE TRAJECTORY CHANGE WILL COME FROM THE
BUMPER EFFECT OF THE STRONG, GALE-FORCE, NORTHEASTERLIES TRAPPED
BETWEEN THE STORM AND THE CHINESE COAST. AFTER BRIEFLY SLOWING DOWN
AS IT RUNS INTO THE NORTHEASTERLY FLOW, TS 30W WILL ACCELERATE
SOUTHWESTWARD TOWARDS THE VIETNAMESE COAST, WHERE IT IS EXPECTED TO
MAKE LANDFALL IN THE VICINITY OF DA NANG AROUND TAU 60. MOST LIKELY
DUE TO THE PERSISTENCE OF THE SOUTHERLY SHEAR, TS 30W HAS FAILED TO
ORGANIZE QUICKLY ENOUGH TO BE ABLE TO INTENSIFY AT THE RATE
ORIGINALLY EXPECTED. THE WINDOW OF OPPORTUNITY REMAINING FOR IT TO
INTENSIFY IS RAPIDLY CLOSING, AND THERE REMAINS ONLY ABOUT 24 HOURS
OF FAVORABLE CONDITIONS TO SUPPORT INTENSIFICATION. THUS, THE PEAK
INTENSITY IS FORECAST TO ONLY REACH 55 KNOTS AT TAU 24, BEFORE THE
ONSET OF RAPID WEAKENING INDUCED BY AN INFLUX OF DRY MID-LEVEL AIR
AND INCREASING SHEAR AS IT MAKES ITS HARD LEFT TURN. BY TAU 48, AS
IT IS APPROACHING THE VIETNAMESE COAST, THE SYSTEM WILL BE
COMPLETELY SMOTHERED IN DRY AIR ABOVE 700MB, BE DEVOID OF
SIGNIFICANT CONVECTION AND RAPIDLY DYING OFF. AT LANDFALL THE
SYSTEM WILL BE A MINIMAL TROPICAL STORM OR STRONG TROPICAL
DEPRESSION AND WILL DISSIPATE OVER SOUTHERN LAOS NO LATER THAN TAU
72. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE FOR THE MOST PART IS
IN GOOD AGREEMENT, THOUGH GFS, GEFS AND GALWEM ARE STICKING TO
THEIR GUNS AND RACING THE SYSTEM OFF TO THE SOUTHWEST AT A MUCH
FASTER PACE THAN THE OTHER MEMBERS OF THE CONSENSUS AND DUE TO
THEIR UNREALISTIC TRACK SPEEDS, THESE MODELS HAVE BEEN DISCARDED
FROM THE CONSENSUS. THE REMAINDER OF THE GUIDANCE IS IN MUCH BETTER
AGREEMENT, WITH 140NM OF CROSS-TRACK SPREAD AT TAU 72, BETWEEN
NAVGEM TO THE NORTH AND JGSM TO THE SOUTH. THE JTWC FORECAST IS
PLACED NEAR THE ECWMF TRACKER THROUGH THE ENTIRE FORECAST PERIOD,
WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT,
WITH ALL MODELS, EXCEPT THE SHIPS MODELS, IN AGREEANCE THAT THE
SYSTEM WILL INTENSIFY UP TO 55 KNOTS BY TAU 24, THEN RAPIDLY WEAKEN
TO DISSIPATION WITHIN 72 HOURS. THE JTWC FORECAST IS PLACED AMONGST
THIS TIGHT GROUPING OF MODELS THROUGH THE FORECAST PERIOD, WITH
HIGH CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: HIGH//
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