WDXS32 PGTW 020300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09S (GRANT) WARNING NR 
032//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.8S 67.3E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 605 NM SOUTH-SOUTHWEST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE (TC) 09S (GRANT) WITH A PARTIALLY EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC) AS ASSOCIATED CONVECTION CONTINUES TO
BECOME SHEARED TO THE SOUTHWEST QUADRANT. ALONG WITH SUSTAINED
VERTICAL WIND SHEAR ABOVE 10 KTS, DRY AIR HAS BEEN PREVALENT
THROUGH THE EASTERN AND NORTHERN SEMICIRCLES, VOIDING MUCH OF THE
REGION OF ANY SIGNIFICANT CONVECTION. ALTHOUGH MUCH OF THE NORTHERN
AND EASTERN SIDES OF THE SYSTEM APPEAR CONVECTION FREE, THIS HAS
REVEALED CURVED LOW-LEVEL CLOUD LINES WRAPPING CYCLONICALLY JUST
BENEATH THE SHORT-LIVED FLARING CONVECTION AS THE SYSTEM TRACKS
WESTWARD. ALOFT, TC 09S IS SUPPORTED BY AN EQUATORWARD OUTFLOW
CHANNEL, OBSERVED ON ANIMATED WATER VAPOR IMAGERY. THE ENVIRONMENT
REMAINS MARGINAL FOR THE SYSTEM, AS DRY AIR CONTINUES TO SUFFOCATE
THE CYCLONES PERIPHERY. THE INITIAL POSITION IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE AFOREMENTIONED FULLY EXPOSED LLCC OBSERVED
ON ANIMATED MSI. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE BASED SUBJECTIVE AGENCY DVORAK ESTIMATES AS LOW AS 30
KTS AND CIMSS OBJECTIVE INTENSITY ESTIMATES RANGING FROM 32-39 KTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NORTHWESTERN EXTENT OF A SUBTROPICAL
RIDGE (STR) LOCATED TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   DEMS: T5.0 - 90 KTS
   CIMSS SATCON: 43 KTS AT 012052Z
   CIMSS ADT: 41 KTS AT 020000Z
   CIMSS D-MINT: 38 KTS AT 012101Z
   CIMSS D-PRINT: 30 KTS AT 020000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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: TC 09S IS FORECASTED TO TRACK
WEST-NORTHWESTWARD OVER THE NEXT 12-18 HOURS ALONG THE NORTHWESTERN
PERIPHERY OF THE STR LOCATED TO THE SOUTHEAST. FOLLOWING TAU 18, TC
09S IS EXPECTED TO BEGIN A SOUTH-SOUTHWESTWARD TRACK THROUGH TAU 96
AS THE DEEP-LAYER STR TO THE SOUTH BUILDS WESTWARD AND THE NEAR
EQUATORIAL RIDGE TO THE NORTH EXTENDS WESTWARD OVER NORTHERN
MADAGASCAR. AFTER TAU 96, THE CYCLONE WILL TAKE ON A SOUTHWESTWARD
TRACK AND BEGIN TO ROUND THE WESTERN PERIPHERY OF THE STR TO THE
SOUTH UNTIL THE END OF THE FORECAST PERIOD. REGARDING INTENSITY, TC
GRANT IS FORECASTED TO MAINTAIN STEADY INTENSITIES NEAR 35 KTS INTO
TAU 48 AS DRY AIR REMAINS PREVALENT, COMPETING WITH WARM SEA
SURFACE TEMPERATURES (ABOVE 26 C) AND SUPPORTIVE UPPER-LEVEL
OUTFLOW. FOLLOWING TAU 48, THE SYSTEM IS FORECASTED TO REGAIN ITS
MOIST CHARACTERISTICS WITH A DECREASE IN DRY AIR AS TC 09S
APPROACHES MOZAMBIQUE. AS THE CYCLONES CORE RE-MOISTENS, SURFACE
INTENSITIES ARE EXPECTED TO INCREASE TO 50 KTS BY TAU 96. FOLLOWING
TAU 96, DECREASING INTENSITIES TO 30 KTS ARE FORECASTED WITH THE
RE-INTRODUCTION OF DRY AIR ALONG THE SYSTEMS EASTERN SEMICIRCLE
THROUGH THE END OF THE FORECAST PERIOD.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE AND ARTIFICIAL
INTELLIGENCE (AI) MODELS CONTINUE TO BE IN GOOD AGREEMENT INTO TAU
72, WITH A CROSS-TRACK SPREAD OF 117 NM. FOLLOWING TAU 72, MODEL
SOLUTIONS BEGIN TO DIVERGE, WITH NAVGEM TAKING ON A NORTHWESTWARD
TRACK. THE REMAINDER OF JTWC NUMERICAL MODEL SOLUTIONS AND AI
SOLUTIONS ILLUSTRATE A SOUTHWESTWARD TRACK BUT VARY IN
ALONG-TRACK SPREAD (391 NM) AS STEERING INFLUENCES FROM THE STR TO
THE SOUTHWEST DIFFER. THE TIGHT GROUPING OF JTWC CONSENSUS
SOLUTIONS LEND HIGH CONFIDENCE TO THE 72 HOUR FORECAST, WHILE THE
DIFFERENCE IN ALONG-TRACK SPREAD LEND MEDIUM CONFIDENCE THEREAFTER.
INTENSITY GUIDANCE IS IN FAIR AGREEMENT, MAINTAINING A 10 KTS
SPREAD BETWEEN 25-40 KTS UNTIL TAU 48 BETWEEN ALL SOLUTIONS.
FOLLOWING TAU 48, UNCERTAINTY INCREASES AS THE GFS DETERMINISTIC
AND COAMPS-TC SOLUTIONS CHARACTERIZE STEADY INTENSITIES OF 35 KTS
UNTIL TAU 120. HAFS-A IS THE ONLY OUTLIER, INCREASING INTENSITIES
TO 75 KTS BY TAU 108. DUE TO THE SPREAD IN EXPECTED INTENSITIES IN
THE LONG-TERM FORECAST, THE JTWC INTENSITY FORECAST IS ASSESSED
WITH MEDIUM CONFIDENCE THROUGH THE 120 HOUR PERIOD.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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