WDXS31 PGTW 032100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04S (FOUR) WARNING NR 
001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.2S 93.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 258 NM NORTHWEST OF COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WHICH IS
DISPLACED TO THE NORTHEAST OF AN AREA OF FLARING CONVECTION. A
031504Z AMSU-B 89GHZ MICROWAVE IMAGE REVEALED A DISORGANIZED AREA
OF CONVECTION ORIENTED DOWN THE SHEAR VECTOR, AND SHALLOW BANDING
FEATURES OUTLINING THE LLCC. THE INITIAL POSITION IS ASSESSED WITH
HIGH CONFIDENCE BASED ON THE EXPOSED LLCC IN THE SHORTWAVE INFRARED
IMAGERY SUPPORTED BY THE AMSU-B IMAGERY. WHILE THE SYSTEM IS NOT
ALL THAT ORGANIZED CONVECTIVELY SPEAKING, A SERIES OF WINDSPEED
SENSORS HAVE PASSED OVER THE SYSTEM OVER THE PAST SIX HOURS OR SO,
INCLUDING A 031124Z SMOS, 031206 SMAP AND A 031508Z ASCAT-B PASS,
AND ALL SHOWED WELL DEFINED LLCC WITH A BAND OF 35-40 KNOT WINDS IN
PLACE ACROSS THE SOUTHERN SEMICIRCLE OF THE CIRCULATION, LENDING
HIGH CONFIDENCE TO THE INITIAL POSITION. THE SYSTEM IS MOVING
TOWARDS THE WEST-SOUTHWEST ALONG THE WESTERN PERIPHERY OF A DEEP
SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST. THE ENVIRONMENT IS
ASSESSED AS MARGINAL, WITH WARM SSTS AND MODERATE POLEWARD OUTFLOW
OFFSET BY MODERATE NORTHEASTERLY VERTICAL WIND SHEAR (VWS).

INITIAL WIND RADII BASIS: SCATTEROMETER AND SMAP DATA

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER STR
CENTERED TO THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.0 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 04S WILL CONTINUE TRACKING WEST-SOUTHWEST
OF THE FIRST 36 HOURS OF THE FORECAST ALONG THE WESTERN SIDE OF THE
STR CENTERED TO THE EAST. THE SYSTEM WILL GRADUALLY SLIDE OVER TO A
MORE WESTWARD TRAJECTORY AS IT COMES UNDER THE STEERING INFLUENCE
OF A STRONG, DEEP STR THAT WILL SET UP SHOP AROUND THE LINE OF THE
20TH LATITUDE. THAT WILL KEEP THE SYSTEM FROM MOVING FURTHER
POLEWARD AFTER ABOUT TAU 36. WITH THE LOW LEVEL STRUCTURE BEING AS
WELL-DEFINED AS IT IS, WITH A WIND FIELD THAT IS BETTER ORGANIZED
THAN THE GLOBAL MODELS ARE DEPICTING, IT HAS A BRIEF WINDOW OF
OPPORTUNITY IN WHICH TO INTENSIFY A BIT. THE LATEST IMAGERY SHOWS
THE CONVECTION BLOWING OFF RAPIDLY TO THE SOUTHWEST, BUT ANOTHER
ROUND OF CONVECTIVE DEVELOPMENT IS LIKELY TO POP-OFF IN THE NEXT 12
TO 24 HOURS. THE ECMWF IN PARTICULAR IS ON BOARD WITH A REDUCTION
IN THE NORTHEASTERLY SHEAR COMPONENT AFTER TAU 12, WHICH WILL ALLOW
FOR THE SYSTEM TO BECOME MARGINALLY BETTER ORGANIZED AND INTENSIFY
UP TO A PEAK OF 40 KNOTS BY TAU 24. CONDITIONS REMAIN STEADY STATE
FROM THERE UNTIL ABOUT TAU 48, WHERE SHEAR WILL START PICKING UP
ONCE MORE AND THE SYSTEM WILL FEEL THE EFFECTS OF SOME DRY AIR
ENTRAINMENT, LEADING TO A SLOW DECREASE IN INTENSITY THROUGH THE
REMAINDER OF THE FORECAST. THE SYSTEM IS EXPECTED TO WEAKEN BELOW
35 KNOTS BY TAU 96, BUT THE REMNANT CIRCULATION IS VERY LIKELY TO
CONTINUE TRACKING WESTWARD AS A DISTINCT ENTITY FOR SOME TIME
AFTERWARDS. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT, WITH MINIMAL
SPREAD IN EITHER THE DETERMINISTIC CONSENSUS MEMBERS OR THE GEFS
AND ECENS ENSEMBLES, THROUGH TAU 96. THUS THE JTWC FORECAST, WHICH
LIES ON THE NORTHERN SIDE OF THE ENVELOPE, IS PLACED WITH HIGH
CONFIDENCE. INTENSITY GUIDANCE IS MIXED, WITH THE DECAY-SHIPS
(NAVGEM) INDICATING INTENSIFICATION UP TO 50 KNOTS, WHILE THE
MAJORITY OF THE RELIABLE GUIDANCE CONCURS ON A PEAK AROUND 40 KNOTS
FOLLOWED BY A SLOW AND GRADUAL WEAKENING THEREAFTER THOUGH THE HWRF
WEAKENS THE SYSTEM MORE RAPIDLY THAN THE OTHER GUIDANCE. THE JTWC
FORECAST CLOSELY FOLLOWS THE HWRF SOLUTION WITH MEDIUM CONFIDENCE. 


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