WDXS31 PGTW 180900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 08S (EIGHT) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.8S 54.3E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 497 NM NORTHEAST OF ANTANANARIVO,
MADAGASCAR
   MOVEMENT PAST 6 HOURS: WESTWARD AT 19 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN
ASYMMETRIC SYSTEM, WITH A PARTIALLY EXPOSED LOW LEVEL CIRCULATION
CENTER (LLCC) TO THE EAST OF A MASS OF CYCLONICALLY CURVED
CONVECTION AND AN ELONGATED BANDING FEATURE WHICH EXTENDS FAR TO
THE SOUTHEAST TOWARDS MAURITIUS. UNFORTUNATELY, THERE HAS BEEN A
LACK OF RECENT MICROWAVE IMAGERY OR SCATTEROMETER DATA TO HELP
CLARIFY THE INITIAL POSITION AND STORM STRUCTURE. THE MOST RECENT
91GHZ MICROWAVE IMAGERY FROM 180142Z SHOWED A FULLY EXPOSED LLCC
EAST OF A RELATIVELY SYMMETRIC AREA OF DEEP CONVECTION.
EXTRAPOLATION OF THE POSITION IN THE LATEST MICROWAVE DATA AND
AGENCY FIX POSITIONS PROVIDED MEDIUM CONFIDENCE TO THIS INITIAL
POSITION. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE,
HEDGED ABOVE THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES BASED
ON PERSISTENCE WITH AN 180222Z SMAP BULLSEYE WHICH SHOWED 41 KNOT
MAXIMUM 1-MIN WINDS IN THE NORTHWESTERN SECTOR. ADDITIONALLY, A
PARTIAL 180625Z ASCAT-B PASS SHOWS SMALL REGION OF 35-40 KNOT WINDS
ABOUT 100NM SOUTHWEST OF THE LLCC. INVEST 90S IS ALSO LURKING TO
THE NORTHWEST, JUST SOUTH OF AGALEGA AS EVIDENCED BY A FULLY
EXPOSED LLCC IN THE ANIMATED MSI. 90S IS MOVING QUICKLY SOUTHWARD
WHILE STRETCHING OUT. HOWEVER, ITS PRESENCE HAS PULLED TC 08S UP TO
THE NORTH OVER THE PAST SIX HOURS. OVERALL CONDITIONS REMAIN
FAVORABLE, WITH WARM SSTS AND GOOD POLEWARD AND EQUATORWARD OUTFLOW
BEING OFFSET BY MODERATE EASTERLY SHEAR.

INITIAL WIND RADII BASIS: PARTIAL SCATTEROMETER DATA AND
PERSISTENCE. 

CURRENT STEERING MECHANISM: NORTHWEST PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   FMEE: T2.5 - 35 KTS
   CIMSS SATCON: 34 KTS AT 180545Z
   CIMSS ADT: 33 KTS AT 180315Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND 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: DUE TO THE INFLUENCE OF INVEST 90S, SLIDING
DOWN THE FAR EASTERN PERIPHERY OF THE BROADER CIRCULATION, TC 08S
HAS TRACKED A BIT NORTH OF WEST OVER THE PAST 6 TO 12 HOURS. THE
LATEST IMAGERY AND MODEL FIELDS SUGGEST 90S HAS ALREADY STARTED TO
BECOME ABSORBED INTO THE LARGER CIRCULATION OF TC 08S. ONCE THIS
PROCESS FINISHES, THE STEERING INFLUENCE OF THE STR TO THE
SOUTHEAST WILL BECOME MORE DOMINANT, PUSHING TC 08S ONTO A MORE
WESTWARD TRACK THROUGH TAU 24. LANDFALL ALONG THE NORTHEAST COAST
OF MADAGASCAR IS EXPECTED JUST PRIOR TO TAU 24. AFTER THIS POINT,
THE STR REORIENTS TO A MORE MERIDIONAL AXIS WHICH WILL PUSH TC 08S
ONTO A MORE SOUTHWESTWARD TRACK THROUGH THE REMAINDER OF THE
FORECAST PERIOD. IN TERMS OF INTENSITY, THE PRESENCE OF INVEST 90S
AND THE PERSISTENT EASTERLY SHEAR HAVE SERVED TO DISRUPT THE
CONSOLIDATION OF THE LOW-LEVEL VORTEX, LEADING TO VERY SLOW
INTENSIFICATION OVER THE PAST DAY. THE LATEST HIGH RESOLUTION MODEL
FIELDS SUGGEST THAT THIS WILL CHANGE ONCE 90S IS ABSORBED. SHEAR IS
EXPECTED TO DECREASE AT THE SAME TIME, WHICH MEANS THERE WILL BE A
BRIEF PERIOD OF TIME WHEN CONDITIONS WILL BE MORE FAVORABLE, JUST
PRIOR TO LANDFALL. THE FORECAST CALLS FOR A PEAK OF 50 KNOTS AT TAU
12, BUT IN ALL LIKELIHOOD THE ACTUAL PEAK COULD BE SLIGHTLY HIGHER
AND WILL OCCUR AT OR NEAR LANDFALL, BETWEEN FORECAST POINTS. ONCE
THE SYSTEM MOVES ASHORE, IT WILL RAPIDLY WEAKEN DUE TO INTERACTION
WITH THE RUGGED TERRAIN OF CENTRAL MADAGASCAR. 

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
GOOD AGREEMENT ONLY THROUGH TAU 12, BUT THEN QUICKLY SEPARATES INTO
TWO CAMPS; THE US MODELS INCLUDING GFS, GFS ENSEMBLE, HWRF AND
COAMPS-TC TRACK THE SYSTEM DUE WEST THEN DOWN THE WEST SIDE OF
MADAGASCAR THROUGH THE FORECAST PERIOD. THE HWRF ACTUALLY TRACKS THE
SYSTEM INTO THE MOZAMBIQUE CHANNEL BY TAU 36. MEANWHILE THE ECMWF,
ECMWF ENSEMBLE, GALWEM, UKMET AND UKMET ENSEMBLE TURN THE SYSTEM
MORE SHARPLY POLEWARD AFTER LANDFALL AND TRACK CLOSER TO THE
EASTERN COAST OF MADAGASCAR, WITH THE ECMWF ENSEMBLE EVEN TAKING
THE VORTEX BACK INTO THE INDIAN OCEAN AFTER TAU 72. THE RESULT IS A
VERY WIDE GUIDANCE ENVELOPE AND HIGH UNCERTAINTY IN THE
POST-LANDFALL FORECAST. THE JTWC TRACK LIES ON THE WESTERN EDGE OF
THE EUROPEAN MODEL CLUSTER, SOUTH OF THE US CLUSTER THROUGH THE
FORECAST PERIOD, BUT CONFIDENCE IS LOW DUE TO THE WIDE SPREAD IN
THE GUIDANCE. INTENSITY GUIDANCE IS IN MUCH BETTER AGREEMENT, WITH
ALL MODELS INDICATING INTENSIFICATION TO A PEAK BETWEEN 50-55 KNOTS
AT TAU 12 FOLLOWED BY RAPID WEAKENING THEREAFTER. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM//
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