WDXS31 PGTW 011500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 11S (ELEVEN) WARNING 
NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.6S 60.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 249 NM NORTHEAST OF PORT LOUIS, MAURITIUS
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 11S WITH A COMPACT, WELL-DEFINED LOW-LEVEL CIRCULATION
CENTER. HIGH EASTERLY VERTICAL WIND SHEAR CONTINUES TO ACT ON THE
SYSTEM, CAUSING THE LLCC TO BE COMPLETELY EXPOSED. RECENTLY,
VIGOROUS BURSTS OF CONVECTION ARE BEGINNING TO APPEAR IN THE
NORTHWESTERN QUADRANT. ENVIRONMENTAL ANALYSIS INDICATES THAT 11S IS
IN A MARGINAL ENVIRONMENT CHARACTERIZED BY WEAK POLEWARD OUTFLOW,
HIGH (20-25 KTS) EASTERLY VERTICAL WIND SHEAR, THE PRESENCE OF DRY
AIR, AND WARM (28-29 C) SEA SURFACE TEMPERATURES. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC
IN ANIMATED MSI. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK AND OBJECTIVE
INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE FROM EARLIER SCATTEROMETER
DATA.

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS
   DEMS: T2.0 - 30 KTS
   FMEE: T2.5 - 35 KTS
   CIMSS ADT: 32 KTS AT 011200Z
   CIMSS AIDT: 33 KTS AT 011200Z
   CIMSS DPRINT: 33 KTS AT 011200Z
   CIMSS DMINT: 33 KTS AT 011000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: DRY AIR

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: 11S IS FORECAST TO TRACK GENERALLY WESTWARD,
ALONG THE NORTHERN PERIPHERY OF THE STR THROUGH TAU 36. AFTER TAU
36, A SECONDARY RIDGE IS EXPECTED TO BUILD TO THE WEST OF THE
SYSTEM, DRIVING IT NORTHWESTWARD. 11S IS FORECAST TO MAKE LANDFALL
ALONG THE EASTERN COAST OF MADAGASCAR AROUND TAU 72. THE VORTEX
WILL THEN TRACK ACROSS THE RUGGED TERRAIN OF MADAGASCAR AND THEN
ENTER THE MOZAMBIQUE CHANNEL AROUND TAU 120. REGARDING INTENSITY,
11S IS FORECAST TO MAINTAIN ITS CURRENT INTENSITY THROUGH TAU 24 AS
THE ENVIRONMENT IS EXPECTED TO REMAIN MARGINAL. AFTER TAU 24,
VERTICAL WIND SHEAR IS EXPECTED TO DROP AND DRY AIR INTRUSION WILL
ABATE, ALLOWING FOR A SLIGHT INTENSIFICATION PHASE AS THE SYSTEM
APPROACHES MADAGASCAR. AFTER MAKING LANDFALL, TERRAIN INTERACTION
WILL ERODE THE VORTEX AND CAUSE WEAKENING. ONCE THE SYSTEM ENTERS
THE MOZAMBIQUE CHANNEL, THE ENVIRONMENT WILL GREATLY IMPROVE. SEA
SURFACE TEMPERATURES WILL BE VERY WARM AND SHEAR WILL BE RELATIVELY
LOW. THIS WILL ALLOW 11S TO REINTENSIFY.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
REGARDING THE TRACK OF 11S THROUGH TAU 72, WITH A 105 NM
CROSS-TRACK SPREAD AT THAT TIME. THIS IS WITHOUT THE PRIMARY
OUTLIER, GALWEM, WHICH HAS A SIGNIFICANTLY FASTER TRACK SPEED THAN
THE REMAINDER OF GUIDANCE. AFTER TAU 72, MODELS DIVERGE TO A 290 NM
CROSS-TRACK SPREAD. THE MAIN REASON FOR THIS BEING THAT GFS HAS A
SHARP SOUTHWESTWARD TURN AFTER TAU 72, KEEPING THE VORTEX OVER
LAND. 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 MODERATE AGREEMENT, WITH ALL
MODELS SUGGESTING INTENSIFICATION AFTER TAU 24, WEAKENING OVER
LAND, AND REINTENSIFICAION WITHIN THE MOZAMBIQUE CHANNEL. AS A 
RESULT, THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO CONSENSUS 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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