WDXS31 PGTW 222100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (EMNATI) WARNING 
NR 
014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.6S 48.8E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 178 NM SOUTH-SOUTHEAST OF ANTANANARIVO,
MADAGASCAR
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS DEEP
CONVECTION WRAPPING AROUND A LOW-LEVEL CIRCULATION CENTER (LLCC)
THAT HAS BEEN OCCASIONALLY ASSOCIATED WITH A RAGGED, CLOUD-FILLED
EYE, WITH AN INTENSE FEEDER BAND WRAPPING AROUND THE SOUTHWESTERN
PERIPHERY. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE
GIVEN THE ALIGNMENT BETWEEN THE BRIEF EIR EYE FEATURE AND THE
FORWARD EXTRAPOLATION OF THE LLCC IN THE 221547Z SSMIS 91GHZ IMAGE.
THE INITIAL INTENSITY IS BASED ON SUBJECTIVE DVORAK ESTIMATE OF
T4.5 ALIGNING WITH A SATCON OF 78 KNOTS. TC 13S IS LOCATED IN A
MARGINALLY FAVORABLE ENVIRONMENT, WITH GOOD POLEWARD OUTFLOW AND
LOW VERTICAL SHEAR OVER MARGINAL SSTS OF 27 DEGREES CELSIUS. THE
SYSTEM IS TRACKING ALONG THE NORTHWESTERN PERIPHERY OF THE DEEP
LAYER STR TO THE SOUTHEAST.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP LAYER SUBTROPICAL RIDGE (STR) TO
THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   FMEE: T5.0 - 90 KTS
   CIMSS SATCON: 78 KTS AT 221548Z
   CIMSS ADT: 57 KTS AT 221815Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 5-10 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: IMMINENT LANDFALL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 13S WILL CONTINUE TRACKING TOWARD THE
SOUTHWEST UNDER THE STEERING INFLUENCE OF THE STR WITH IMMINENT
LANDFALL OVER THE SOUTHEASTERN COAST OF MADAGASCAR. AS THE SYSTEM
CROSSES THE ISLAND, STEADY WEAKENING IS FORECAST BEFORE EMERGING
OVER THE MOZAMBIQUE CHANNEL BEYOND TAU 24. BEYOND TAU 36, A GRADUAL
TURN TOWARD THE SOUTH IS FORECAST AS THE SYSTEM ROUNDS THE WESTERN
PERIPHERY OF THE STR. THE WEAKER VORTEX, COMBINED WITH STRONG
VERTICAL WIND SHEAR (30+ KNOTS) AND COOL SSTS (24C) WILL INDUCE TC
13S TO BEGIN SUBTROPICAL TRANSITION AROUND TAU 48 BEFORE BECOMING A
FULLY SUBTROPICAL SYSTEM BY TAU 72.

MODEL DISCUSSION: NUMERICAL MODELS ARE GENERALLY IN GOOD AGREEMENT
WITH NAVGEM AS THE WESTERN OUTLIER AND THE GFS AS THE EASTERN
OUTLIER. BECAUSE OF THE UNCERTAINTIES ASSOCIATED WITH IMMINENT LAND
INTERACTION, THERE IS OVERALL MEDIUM CONFIDENCE IN THE JTWC TRACK
AND INTENSITY FORECASTS.

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