WDXS31 PGTW 100900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04S (CHIDO) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.6S 60.8E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 605 NM NORTH-NORTHEAST OF PORT LOUIS,
MAURITIUS
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE O4S (CHIDO) WITH AN IMPROVED APPEARANCE, BUT STILL WITH AN
ASYMMETRICAL WIND FIELD DUE TO THE SLIGHTLY VERTICALLY TILTED VORTEX
AND EASTERLY SHEAR. STRONGER WINDS CAN BE SEEN ALONG THE WESTERN
PERIPHERY OF THE LOW-LEVEL CIRCULATION CENTER (LLCC). PERSISTENT
BURSTS OF DEEP CONVECTION OBSCURE THE LLCC, WITH A WARM SPOT
RECENTLY APPEARING OVER THE CENTER RIGHT AROUND 0600Z. THE OUTFLOW
PATTERN HAS IMPROVED AND BECOME MORE RADIAL OVER THE PAST 6 HOURS
WITH CIRRUS FILAMENTS EXTENDING OUTWARD IN ALL DIRECTIONS.
ENVIRONMENTAL ANALYSIS INDICATES A MARGINALLY FAVORABLE ENVIRONMENT
FOR DEVELOPMENT CHARACTERIZED BY THE MODERATE RADIAL OUTFLOW ALOFT
AND WARM (28-29 C) SEA SURFACE TEMPERATURES, OFFSET BY THE MODERATE
TO HIGH (20-25 KTS) EASTERLY VERTICAL WIND SHEAR. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE OBSCURED
LLCC IN ANIMATED MSI. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK AND OBJECTIVE
INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: SMOS DATA

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   FMEE: T3.5 - 55 KTS
   FIMP: T3.5 - 55 KTS
   CIMSS ADT: 55 KTS AT 100600Z
   CIMSS AIDT: 46 KTS AT 100600Z
   CIMSS DPRINT: 46 KTS AT 100600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: INCREASED THE PEAK INTENSITY FROM 60
KTS TO 80 KTS AT TAU 48.

FORECAST DISCUSSION: TC 04S IS FORECAST TO CONTINUE TRACKING
WESTWARD ALONG THE NORTHERN PERIPHERY OF THE STR THROUGH TAU 48.
AFTER TAU 48, THE RIDGE TO THE SOUTH BUILDS AND THE SYSTEM BEGINS
TO TRACK MORE WEST-SOUTHWESTWARD ALONG THE NORTHEASTERN PERIPHERY
OF THE RIDGE. THE WEST-SOUTHWESTWARD TRACK WILL THEN CONTINUE
THROUGH THE REMAINDER OF THE FORECAST PERIOD. JUST AFTER TAU 72,
04S IS FORECAST TO SKIRT ALONG THE NORTHERN TIP OF MADAGASCAR AS IT
ENTERS THE MOZAMBIQUE CHANNEL AND APPROACHES THE COAST OF
MOZAMBIQUE NEAR TAU 120. REGARDING INTENSITY, 04S IS FORECAST TO
CONTINUE INTENSIFYING THROUGH TAU 48 AS IT BECOMES VERTICALLY
ALIGNED. RECENT MODEL GUIDANCE HAS DEPICTED A QUICKER ONSET OF THIS
ALIGNMENT, ALLOWING FOR A HIGHER PEAK INTENSITY. AFTER TAU 48, THE
ENVIRONMENT WILL BEGIN TO WORSEN AS EASTERLY VERTICAL WIND SHEAR
INCREASES. THIS WILL CAUSE 04S TO START A WEAKENING TREND WHICH
WILL PERSIST THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD.
ADDITIONALLY, AS THE SYSTEM TRACKS ACROSS THE NORTHERN TIP OF
MADAGASCAR TERRAIN INTERACTION WILL AID IN THE WEAKENING OF THE
VORTEX. AS A RESULT, 04S IS FORECAST TO DROP TO AROUND 35 KTS AT
TAU 120, JUST OFF THE COAST OF NORTHERN MOZAMBIQUE. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
REGARDING THE TRACK OF 04S THROUGH TAU 72, WITH A 115 NM
CROSS-TRACK SPREAD AT THAT TIME. AFTER TAU 72, MODELS BEGIN TO
DIVERGE. NAVGEM AND GALWEM TAKE THE SYSTEM FURTHER SOUTH INTO
MADAGASCAR, WHICH CAUSES THEM TO TRACK THE VORTEX MUCH FURTHER
SOUTHWARD WITHIN THE MOZAMBIQUE CHANNEL THAN THE REMAINDER OF
GUIDANCE. THE JTWC TRACK FORECAST IS PLACED CLOSER TO THE MAIN
GROUPING WITH HIGH CONFIDENCE THROUGH TAU 72 AND MEDIUM CONFIDENCE
THEREAFTER. INTENSITY GUIDANCE IS IN GOOD AGREEMENT WITH THE
EXCEPTION OF THE MAJOR OUTLIER, HAFS-A. HAFS-A SUGGESTS A PEAK
INTENSITY OF AROUND 120 KTS AT TAU 48, WHILE THE REMAINDER OF
GUIDANCE SUGGESTS A PEAK OF AROUND 65-85 KTS. THE JTWC INTENSITY
FORECAST IS PLACED NEAR MAJORITY THROUGHOUT THE FORECAST PERIOD
WITH OVERALL MEDIUM CONFIDENCE. 

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