WDXS32 PGTW 040300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09S (GRANT) WARNING NR 
036//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.5S 62.8E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 418 NM NORTHEAST OF PORT LOUIS, MAURITIUS
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TC 09S HAS WEAKENED SLIGHTLY OVER THE PAST 12 HOURS IN RESPONSE TO 
MARGINAL ENVIRONMENTAL CONDITIONS. ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY DEPICTS DEEP CONVECTION FLARING OVER THE WESTERN
PORTION OF A LOW-LEVEL CIRCULATION EVIDENT IN A 032126Z GMI PASS. THE 
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE DOWNSTREAM FROM THE 
CIRCULATION CENTER, WHICH APPEARS IN 37 GHZ IMAGERY FROM THE 032126Z 
GMI PASS. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM 
CONFIDENCE FAVORING THE LOWER END OF SUBJECTIVE DVORAK AND AUTOMATED 
INTENSITY ESTIMATES LISTED BELOW IN LIGHT OF EARLIER ASCAT DATA, 
INCLUDING A 031703Z METOP-C PASS, THAT SHOWED LOW-LEVEL WIND SPEED 
PEAKING IN THE 25-30 KT RANGE.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGING TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   CIMSS SATCON: 39 KTS AT 032105Z
   CIMSS ADT: 45 KTS AT 032100Z
   CIMSS AIDT: 41 KTS AT 040000Z
   CIMSS D-MINT: 28 KTS AT 032129Z
   CIMSS D-PRINT: 23 KTS AT 032330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE WESTWARD
   OTHER FACTORS: ENTRAINMENT OF DRIER AIR

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST SHIFT HAS SHIFTED
SLIGHTLY TO THE SOUTH. HOWEVER, THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC 09S WILL CONTINUE TO TRACK
WEST-SOUTHWESTWARD THROUGHOUT THE FORECAST PERIOD FOLLOWING THE
STEERING FLOW ASSOCIATED WITH A SUBTROPICAL STEERING RIDGE TO THE
SOUTH. ALTHOUGH MAXIMUM SUSTAINED SURFACE WIND SPEEDS HAVE FALLEN
BELOW THE WARNING THRESHOLD OF 35 KNOTS DUE TO MARGINAL UPPER-LEVEL
CONDITIONS AND ENTRAINMENT OF DRIER AIR FROM THE SURROUNDING
ENVIRONMENT, THE SYSTEM MAY EXPERIENCE A SMALL BOOST DUE TO
ENHANCED WESTWARD OUTFLOW ALOFT AND LOW VERTICAL WIND SHEAR BY TAU
24. HOWEVER, AFTER TAU 48, VERTICAL WIND SHEAR IS EXPECTED TO
INCREASE APPRECIABLY AND DRIVE DISSIPATION BEFORE THE CENTER
REACHES THE EASTERN COAST OF MADAGASCAR.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
REGARDING THE OVERALL FORECAST SCENARIO WITH RESPECT TO BOTH TRACK
AND INTENSITY, ALTHOUGH CONSENSUS TRACK SOLUTIONS FAN OUT FROM TAU
24 ONWARD DUE TO VARYING DEPICTIONS OF THE STEERING FLOW AND
STORM STRUCTURE. THE CURRENT TRACK FORECAST LIES WITHIN AN ENVELOPE
ENCOMPASSING THE MAJORITY OF CONSENSUS MODEL SOLUTIONS AND A BIT
POLEWARD OF THE PREVIOUS JTWC FORECAST. GFS, HAFS-A, AND COAMPS-TC
INDICATE A STEADY STATE OVER THE NEXT 48 HOURS FOLLOWED BY
ADDITIONAL DISSIPATION WHILE HWRF AND THE STATISTICAL-DYNAMICAL
SHIPS MODEL SOLUTIONS SUPPORT A NEAR-TERM BUMP TO 35 KNOTS OR SLIGHTLY
HIGHER. THE CURRENT INTENSITY FORECAST FAVORS A SMALL INCREASE IN
INTENSITY DUE TO ANTICIPATED SUPPORTIVE UPPER-LEVEL FLOW, ALTHOUGH
A STEADY STATE OR CONTINUED WEAKENING TO DISSIPATION IS POSSIBLE IN 
LIGHT OF RECENT TRENDS AND ANTICIPATED CONTINUATION OF DRY AIR 
ENTRAINMENT.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM//
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