WDXS31 PGTW 130900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12S (TWELVE) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.9S 60.9E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 374 NM NORTHEAST OF PORT LOUIS, MAURITIUS
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
COMPACT AND IRREGULAR SYSTEM WITH FLARING CENTRAL CONVECTION BUT NO
FORMATIVE RAIN BANDS. THE INITIAL POSITION AND INTENSITY ARE PLACED
WITH HIGH CONFIDENCE BASED ON A 130458Z ASCAT BULLSEYE PASS SHOWING
A TIGHT LOW LEVEL CIRCULATION WITH A SMALL CLUSTER OF 35-KT WIND
BARBS ALONG THE SOUTHEAST QUADRANT. ANALYSIS INDICATES A
MARGINAL ENVIRONMENT WITH WARM (28-29) SST, LOW-MODERATE (15-20KT)
VWS, AND WEAK POLEWARD UPPER LEVEL OUTFLOW. THE CYCLONE IS TRACKING 
ALONG THE NORTHERN PERIPHERY OF A LOW REFLECTION OF THE STR TO THE
SOUTH-SOUTHEAST.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
SOUTH-SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   FMEE: T2.0 - 30 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK 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 12S WILL CONTINUE ON ITS CURRENT TRACK
UNDER THE STEERING INFLUENCE OF THE STR. NEAR TAU 48, A SECONDARY
STR APPROACHING FROM THE SOUTHWEST WILL ASSUME STEERING AND DRIVE
THE SYSTEM MORE WEST-NORTHWESTWARD, MAKING LANDFALL OVER NORTHERN
MADAGASCAR BEFORE TAU 72. THE MARGINAL ENVIRONMENT WILL, AT BEST,
SUSTAIN THE CURRENT INTENSITY AS THE CYCLONE TRACKS OVER THE WARM
INDIAN OCEAN TOWARD NORTHERN MADAGASCAR. AFTER TAU 48, COLD DRY AIR
INTRUSION AND LANDFALL INTO MADAGASCAR WILL LEAD TO RAPID DECAY AND
EVENTUAL DISSIPATION BY TAU 72. GIVEN THE ALONG-TRACK MARGINAL
ENVIRONMENT, THERE IS A POSSIBILITY THAT TC 12S WILL DISSIPATE OVER
WATER BEFORE REACHING MADAGASCAR.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL GOOD AGREEMENT
ALBEIT WITH A WIDE SPREAD AFTER TAU 36, FANNING OUT TO OVER 450NM
BY TAU 72. NAVGEM IS THE EXTREME RIGHT-OF-TRACK OUTLIER DRIVING THE
VORTEX INTO A SHARP U-TURN EQUATORWARD AFTER TAU 24. THIS, PLUS THE
UNCERTAINTY IN THE STRENGTH OF THE SYSTEM AS IT NAVIGATES A
MARGINAL ENVIRONMENT, LENDS LOW CONFIDENCE IN THE INITIAL JTWC
TRACK AND INTENSITY FORECASTS. 

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