WDPN32 PGTW 020900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (SAOLA) WARNING NR 
039//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.7N 111.9E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 133 NM WEST-SOUTHWEST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A SYSTEM
WHICH IS UNDERGOING A SIGNIFICANT WEAKENING AND COMING UNDER THE
INFLUENCE OF EVER INCREASING SHEAR. THE MSI SHOWS A PRONOUNCED
CIRCULATION CENTER MOVING WEST-NORTHWESTWARD INTO SOUTHERN CHINA,
BUT THIS IS NOT THE CENTER YOU ARE LOOKING FOR. THE LOW LEVEL
CIRCULATION CENTER (LLCC), AS DETERMINED BY RADAR DATA, SYNOPTIC
OBSERVATIONS AND A 010547Z AMSR2 37GHZ MICROWAVE IMAGE, WAS MUCH
FURTHER TO THE SOUTH. THE 0600Z OBSERVATION FROM YANGJIANG SHOWED
WINDS FROM THE EAST AT 19 KNOTS, WHICH PROVIDES SOLID EVIDENCE TO
BACK UP THE RADAR DEPICTION THAT THE LLCC WAS TO THE SOUTH OF THE
STATION. THE AMSR2 IMAGERY, WHILE NOT AS CONCLUSIVE, STILL SHOWS A
SHARPLY DEFINED LLCC STRADDLING THE COASTLINE AT THE SYNOPTIC TIME.
HENCE THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE.
INTENSITY ESTIMATION IS CHALLENGING DUE TO A LACK OF AVAILABLE
DATA, AS MOST OF THE REPORTING AGENCIES ARE CHASING THE MID-LEVEL
ROTATION OVER LAND AND NOT REPORTING AN INTENSITY. WHAT DATA WAS
AVAILABLE INCLUDING AN ADT ESTIMATE OF T3.9, AIDT OF 60 KNOTS AND A
SATCON ESTIMATE OF 63 KNOTS, ALONG THE FACT THAT THE SYSTEM IS
CLEARLY SHEARED AND STRADDLING THE COASTLINE, SUPPORTED THE INITIAL
INTENSITY WITH LOW CONFIDENCE. NOW THAT THE SYSTEM IS OVER LAND,
CONDITIONS ARE RAPIDLY DETERIORATING, WITH THE ROBUST POLEWARD
OUTFLOW OFFSET BY THE MODERATE SOUTHEASTERLY SHEAR, FRICTIONAL
EFFECTS, DRY AIR ENTRAINMENT AND THE LACK OF AN ENERGY SOURCE TO
FEED THE SYSTEM.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHEASTERN SIDE OF A LOW TO MID-LEVEL
RIDGE OVER CHINA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   RJTD: T4.5 - 77 KTS
   RCTP: T4.0 - 65 KTS
   CIMSS ADT: 63 KTS AT 020530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

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: THE LAST COUPLE OF HOURS OF RADAR DATA
SUGGESTS THE LLCC IS TRACKING JUST NORTH OF DUE WEST AND IS NOW A
FAIR DISTANCE INLAND. THE SYSTEM IS FORECAST TO CONTINUE TRACKING
WESTWARD FOR THE NEXT 12 HOURS BEFORE TURNING MORE SOUTHWESTWARD
AND TRACKING INTO THE NORTHERN PORTION OF THE GULF OF TONKIN BY TAU
24. AFTER TAU 24 THE SYSTEM IS FORECAST TO FOLLOW A GENTLY CURVING
TRACK ROUGHLY PARALLEL THE COAST OF HAINAN ISLAND BEFORE EVENTUALLY
MOVING ASHORE OVER SOUTHWESTERN HAINAN BY TAU 96. PASSAGE OVER LAND
WILL RESULT IN SIGNIFICANT WEAKENING OVER THE NEXT 24 HOURS, WITH
THE SYSTEM EXPECTED TO EMERGE INTO THE GULF OF TONKIN AS A 40 KNOT
TROPICAL STORM, IN THE BEST CASE SCENARIO. THE SYSTEM WILL SLOWLY
WEAKEN AS IT TRACKS SOUTHWARD ALONG THE HAINAN COAST BEFORE
EVENTUALLY DISSIPATING OVER LAND BY THE END OF THE FORECAST.

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE DEPICTS
A WEAK BIFURCATION, SPLIT BETWEEN THE ECMWF, HAFS-A, AND COAMPS-TC
AND THE GFS, GEFS, NAVGEM AND THEIR ENSEMBLE MEANS. THE FORMER
GROUP TRACK THE SYSTEM STRAIGHT SOUTHWESTWARD THROUGH THE ENTIRE
FORECAST PERIOD, WITH THE SYSTEM DYING OVER NORTHERN VIETNAM. THE
SECOND GROUP, WITH SOME MINOR VARIATIONS, FOLLOW THE JTWC TRACK,
THOUGH THE GFS TAKES THE SYSTEM BACK INTO THE SOUTH CHINA SEA BY
TAU 96 AND THE ECMWF ENSEMBLE MEAN KEEPS THE SYSTEM OFFSHORE IN THE
GULF OF TONKIN. THE GFS APPEARS TO BE PULLING THE SYSTEM BACK TO
THE NORTHEAST IN THE LEE OF TY 10W (HAIKUI) AS IT ALSO TRACKS BACK
TO THE EAST AFTER TAU 96 IN THE GFS MODEL. IN THE END ANALYSIS,
CROSS-TRACK SPREAD INCREASES TO 460NM BY TAU 96, GENERATING LOW
CONFIDENCE IN THE JTWC FORECAST TRACK. INTENSITY GUIDANCE IS IN
GOOD AGREEMENT ON THE OVERALL WEAKENING TREND, WITH DISSIPATION BY
TAU 96. HOWEVER, IF THE SYSTEM HOLDS ON LONG ENOUGH AND FOLLOWS THE
GFS SOLUTION, IT IS POSSIBLE IT COULD REINTENSIFY. 

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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