WDXS31 PGTW 270300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 08S (EIGHT) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.4S 83.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 862 NM SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) INDICATES THAT TC
08S HAS STEADILY CONSOLIDATED AND DEVELOPED AN IMPROVED CONVECTIVE
STRUCTURE OVER THE PAST SIX HOURS. AT THE 270000Z HOUR, A SMALL
BURST OF CONVECTION WAS SEEN TO BE DEVELOPING NEAR THE ASSESSED
CENTER AND OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC). A
262229Z SSMIS 91GHZ MICROWAVE IMAGE DEPICTED WELL DEFINED
CONVECTIVE BANDS TO THE NORTH AND SOUTH, WRAPPING INTO A THE
OBSCURED LLCC. THE INITIAL POSITION IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE AFOREMENTIONED MICROWAVE IMAGERY. THE
INITIAL INTENSITY OF 35 KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE,
ON THE HIGHER END OF AGENCY DVORAK CURRENT INTENSITY ESTIMATES
RANGING BETWEEN T2.0 (PGTW) TO T2.5 (FMEE) AND THE OVERALL IMPROVED
CONVECTIVE AND MICROWAVE STRUCTURE. THE SYSTEM LIES IN AN OVERALL
MARGINALLY FAVORABLE ENVIRONMENT, WITH THE VERY WARM (28-29C) SSTS
AND RELATIVELY LOW VWS BEING OFFSET SOMEWHAT BY FAIR OUTFLOW ALOFT,
SOME MID-LEVEL DRY AIR INTRUSION AND THE SMALL SIZE OF THE SYSTEM.

INITIAL WIND RADII BASIS: OTHER 

CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE SOUTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   FMEE: T2.5 - 35 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TC 08S HAS CONSOLIDATED WITHIN THE FAR EASTERN
END OF THE MONSOON TROUGH, AND HAS SEPARATED ITSELF INTO A DISTINCT
ENTITY OVER THE PAST 24 HOURS. OVER THE PAST 12 HOURS, IT HAS
BECOME INCREASINGLY ORGANIZED AND WELL DEFINED AS A TROPICAL
CYCLONE. THE SYSTEM IS FORECAST TO TRACK WEST-SOUTHWESTWARD THROUGH
48 HOURS ALONG THE NORTH-NORTHWESTERN PERIPHERY OF THE STR TO THE
SOUTH. WHILE THE SCATTEROMETER AND MODEL FIELDS SUGGEST THE
PRESENCE OF A CIRCULATION TO THE NORTH WITHIN THE MONSOON TROUGH,
WHICH IS FAIRLY CLOSE TO TC 08S, AT THIS TIME IT IS NOT EXPECTED TO
SIGNIFICANTLY IMPACT THE TRACK OF TC 08S. BY TAU 48, THE RIDGE TO
THE SOUTH WILL WEAKEN DUE TO PASSAGE OF A MID-LATITUDE TROUGH,
THOUGH THE IMPACT ON TC 08S IS EXPECTED TO BE MINIMAL, WITH ONLY A
SLOWDOWN IN TRACK SPEED EXPECTED. BY TAU 72, A BUILDING RIDGE TO
THE SOUTHWEST WILL TAKE OVER STEERING, PUSHING TC 08S ONTO A MORE
WESTWARD TRACK THROUGH THE REMAINDER OF THE FORECAST. ENVIRONMENTAL
CONDITIONS ARE COMPLEX, WITH MULTIPLE COMPETING FACTORS INFLUENCING
THE FORECAST. IN THE NEAR-TERM, THE LACK OF A STRONG OUTFLOW
MECHANISM WILL OFFSET THE LOW VWS AND WARM SSTS, LEADING TO SLOW
BURSTS OF INTENSIFICATION FOLLOWED BY PERIODS OF STEADY INTENSITY.
AFTER TAU 48, THE SYSTEM WILL BRIEFLY ESTABLISH A POLEWARD OUTFLOW
CHANNEL, ALLOWING FOR A SHORT BURST OF INTENSIFICATION TO A PEAK OF
55 KNOTS AT TAU 72. AFTER THIS POINT, INCREASING DRY AIR INTRUSION,
NORTHEASTERLY SHEAR AND CONVERGENT FLOW ALOFT WILL CONSPIRE TO
WEAKEN THE SYSTEM THROUGH THE END OF THE FORECAST PERIOD.  

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU
72, THEN DEPICTS SIGNIFICANT DIVERGENCE, WITH THE UKMET ENSEMBLE,
GALWEM AND ECMWF ENSEMBLE PEELING OFF TO THE SOUTH, WHILE THE GFS
ENSEMBLE AND ECMWF DETERMINISTIC DRIFT OFF TO THE NORTH OF THE
TIGHTEST GROUPING OF GUIDANCE MEMBERS. SPREAD IS ONLY 70NM AT TAU
72, BUT INCREASES TO 160NM AT TAU 120. THE JTWC FORECAST TRACK LIES
ON THE NORTHERN SIDE OF THE GUIDANCE ENVELOPE THROUGH THE FORECAST
PERIOD WITH MEDIUM TRENDING TO LOW. INTENSITY GUIDANCE IS MIXED,
WITH THE DECAY SHIPS-GFS INDICATING STEADY INTENSIFICATION TO A
PEAK OF 95 KNOTS BY THE END OF THE FORECAST PERIOD, WHILE THE
COAMPS-TC DEPICTS BASICALLY STEADY INTENSITY THROUGH THE PERIOD,
AND THE BULK OF THE REMAINDER OF THE GUIDANCE MEMBERS BETWEEN 55
AND 70 KNOTS. THE JTWC FORECAST TRACKS SLIGHTLY BELOW THE CONSENSUS
THROUGH TAU 72, THEN WELL BELOW THE MEAN THROUGH THE END OF THE
FORECAST PERIOD. CONFIDENCE IS LOW WITH THE OVERALL INTENSITY
FORECAST DUE TO THE VERY LARGE SPREAD IN THE GUIDANCE. 

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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