WDPN33 PGTW 122100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 24W (KOMPASU) WARNING 
NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.1N 114.5E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 193 NM SOUTH OF HONG KONG
   MOVEMENT PAST 6 HOURS: WESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A VERY
LARGE TROPICAL CYCLONE, WITH THE OUTER BANDS EXTENDING AS FAR NORTH
AS TAIWAN AND SOUTH FAR INTO THE SOUTH CHINA SEA. THE PREVIOUSLY
DISORGANIZED LOW LEVEL CIRCULATION CENTER (LLCC) HAS BECOME
INCREASINGLY ORGANIZED OVER THE PAST SIX HOURS, WITH DEEP FLARING
CONVECTION BLOOMING JUST WEST OF THE ASSESSED LLCC. UNFORTUNATELY,
THERE HAS NOT BEEN ANY RECENT MICROWAVE IMAGERY AND THE CENTER IS
JUST OUTSIDE OF RADAR COVERAGE, SO THE INITIAL POSITION IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON TRACKING OF THE LLCC PRIOR TO ITS
OBSCURATION BY THE FLARING CONVECTION. THE INITIAL INTENSITY OF 55
KNOTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON A CONGRUENCE OF
AGENCY SUBJECTIVE DVORAK ESTIMATES, AND HEDGED SLIGHTLY HIGHER THAN
THE ADT OBJECTIVE ESTIMATES. DUE TO THE LARGE NATURE OF THE SYSTEM,
GALE TO STORM FORCE WINDS EXTEND OUTWARDS TO THE SOUTHERN COAST OF
CHINA AND NORTHEASTWARD OUT APPROXIMATELY 250NM EAST AND SOUTHEAST,
AS CONFIRMED BY SHIP OBSERVATIONS TO THE SOUTHEAST AND NORTH.
ADDITIONALLY, DONGSHA ISLAND HAS BEEN REPORTING EASTERLY WINDS OF
56 KNOTS FOR SEVERAL HOURS, WHICH PROVIDES ADDITIONAL CONFIDENCE TO
THE 50 KNOT WIND RADII. THE ENVIRONMENT IS MARGINALLY FAVORABLE,
TRENDING TOWARDS MARGINAL, WITH WARM SSTS AND STRONG EQUATORWARD
OUTFLOW BEING OFFSET BY MODERATE TO STRONG EASTERLY SHEAR.

INITIAL WIND RADII BASIS: PERSISTENCE WITH EARLIER SCATTEROMETER
DATA AND SURFACE OBSERVATIONS.  

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED OVER CENTRAL CHINA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS ADT: 41 KTS AT 121740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL STORM KOMPASU HAS PICKED UP A GOOD
HEAD OF STEAM AS IT TRACKS RAPIDLY WESTWARD ALONG THE SOUTHERN
PERIPHERY OF THE STR TO THE NORTH, WITH A SPEED OVER GROUND OF 16
KNOTS. THE SYSTEM IS FORECAST TO MAINTAIN A WESTWARD TRACK THROUGH
THE DURATION OF THE FORECAST, BUT SHOULD SLOW AFTER LANDFALL ON
HAINAN AS THE STEERING GRADIENT WEAKENS SLIGHTLY. FIRST LANDFALL IS
EXPECTED ALONG THE EAST COAST OF HAINAN WITHIN THE NEXT 12 TO 15
HOURS, FOLLOWED BY A SECOND LANDFALL ALONG THE COAST OF NORTH
VIETNAM BETWEEN TAUS 36 AND 48. WHILE CONVECTION IS FLARING AND
LOOKS IMPRESSIVE, THE PERSISTENT, MODERATE EASTERLY SHEAR IS
PRECLUDING DEVELOPMENT OF A SOLID CORE OF DEEP CONVECTION, AND THUS
THE FLARE UP OF CONVECTION IS NOT EXPECTED TO PERSIST. REGARDLESS
OF ITS CURRENT APPEARANCE, THE SYSTEM IS NOT FORECAST TO INTENSIFY
FURTHER, AND WILL EXPERIENCE SOME RAPID WEAKENING WHILE PASSING
OVER HAINAN, THOUGH IT IS EXPECTED TO EMERGE INTO THE GULF OF
TONKIN AS A TROPICAL STORM. ONCE ASHORE IN VIETNAM, THE SYSTEM WILL
RAPIDLY DISSIPATE OVER LAOS NO LATER THAN TAU 72. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD AGREEMENT THROUGH
LANDFALL IN VIETNAM, WITH THE TRACKERS SCATTERING THEREAFTER AS THE
MODELS LOSE THE VORTEX. THE JTWC TRACK REMAINS CONSISTENT WITH THE
PREVIOUS FORECAST, THOUGH A BIT FASTER IN LIGHT OF THE RECENT
UPTICK IN TRACK SPEED. TIMING OF LANDFALL AT HAINAN HAS THUS BEEN
MOVED EARLIER. THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK.
INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT, AND LENDS HIGH
CONFIDENCE TO THE JTWC FORECAST. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: HIGH//
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