WDXS31 PGTW 261500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 20S (GAMANE) 
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.5S 50.7E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 593 NM NORTHWEST OF PORT LOUIS, MAURITIUS
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TC 20S (GAMANE) HAS QUICKLY CONSOLIDATED OVER THE PAST 12 HOURS WITH 
A 20 KNOT INCREASE IN INTENSITY OVER THAT INTERVAL. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL CYCLONE (TC)
20S (GAMANE) AS A COMPACT SYSTEM WITH PERSISTENT DEEP CONVECTION
OVER THE CENTER OF AN OBSCURED LOW-LEVEL CIRCULATION (LLCC). A
PRONOUNCED CONVECTIVE BAND TO THE EAST OF THE LLCC CAN BE SEEN IN
THE ANIMATED IMAGERY SURROUNDING THE CIRCULATION AND EXTENDING INTO
THE NORTHERN PERIPHERY. A 260616Z ASCAT-C IMAGE REVEALS 40-45 KTS
IN THE SOUTHERN SEMICIRCLE OF THE LLCC, AND TC 20S HAS CONTINUED TO
STRUCTURALLY IMPROVE SINCE THEN. THE CURRENT ENVIRONMENT IS
ASSESSED AS FAVORABLE CHARACTERIZED BY STRONG POLEWARD OUTFLOW
ALOFT (ENHANCED BY A POINT SOURCE OVERHEAD AND A JET MAX TO THE
SOUTH), VERY LOW (0-5 KTS) VERTICAL WIND SHEAR (VWS), AND WARM
(29-30 C) SEA SURFACE TEMPERATURES. THE ONLY POSSIBLE HINDRANCE TO
THE SYSTEM IS ITS PROXIMITY TO LAND WITH POTENTIAL FRICTION INDUCED 
ON THE LOWER LEVELS. THE INITIAL POSITION IS PLACED WITH MEDIUM 
CONFIDENCE BASED ON A 261200Z MET-9 VISIBLE SATELLITE IMAGE SHOWING A 
FORMATIVE EYE FEATURE. THE INITIAL INTENSITY OF 55 KTS IS ASSESSED 
WITH MEDIUM CONFIDENCE BASED ON SUBJECTIVE AND OBJECTIVE DVORAK 
ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   DEMS: T3.5 - 55 KTS
   FMEE: T4.0 - 65 KTS
   CIMSS AIDT: 52 KTS AT 261200Z
   CIMSS ADT: 53 KTS AT 261200Z
   CIMSS DPRINT: 55 KTS AT 261200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 18S IS FORECAST TO BEGIN TRACKING
SOUTH-SOUTHWESTWARD OVER THE NEXT 24 HOURS AS IT EXITS THE
COMPETING STEERING ENVIRONMENT AND TRACKS ALONG THE WESTERN
PERIPHERY OF A SUBTROPICAL RIDGE (STR) TO THE EAST. AFTER TAU 24,
TC 20S IS FORECAST TO TRACK SOUTHWARD THROUGH TAU 48 AS IT ROUNDS
THE STR. AFTER TAU 48, THE SYSTEM IS EXPECTED TO BEGIN A
SOUTHEASTWARD TRACK AS THE STR PROPAGATES TO THE EAST. TC 20S IS
THEN FORECAST TO CONTINUE ON THE SOUTHEASTWARD TRACK THROUGH THE
REMAINDER OF THE FORECAST PERIOD. REGARDING THE JTWC INTENSITY
FORECAST, TC 20S IS FORECAST TO CONTINUE TO INTENSIFY TO A PEAK OF
85 KTS NEAR TAU 24 AS VWS VALUES CONTINUE TO BE LOW AND DIVERGENCE
ALOFT CONTINUES TO BE STRONG. TC 20S IS FORECAST TO MAINTAIN 85 KTS
THROUGH TAU 36, AND THEN WEAKEN TO 70 KTS NEAR TAU 48 IN RESPONSE
TO LAND INTERACTION ALONG THE NORTHEASTERN COAST OF MADAGASCAR.
AFTER TAU 48, THE SYSTEM IS FORECAST TO CONTINUE WEAKENING TO 60
KTS NEAR TAU 72, 55 KTS NEAR TAU 96, AND 45 KTS NEAR TAU 120. THIS
IS DUE PREDOMINATELY TO INCREASING VWS VALUES AND DRY AIR BEGINNING
TO ENTRAIN INTO THE SYSTEM FROM THE WEST. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN RATHER POOR
AGREEMENT. UKMET AND GALWEM BOTH TRACK THE SYSTEM EASTWARD AFTER
TAU 36, AND CONFLICTS WITH THE REST OF THE GUIDANCE.  THERE IS ALSO
CONSIDERABLE ALONG-TRACK SPREAD WITH ECMWF, HWRF, AND HAFS-A
SUGGESTING A SLOWER TRACK AFTER TAU 48. GFS AND NAVGEM BOTH
SUGGESTS A MUCH FASTER TRACK SPEED AFTER TAU 48. AS A RESULT, THE
JTWC FORECAST TRACK IS PLACED WITH OVERALL LOW CONFIDENCE.
INTENSITY GUIDANCE IS ALSO IN RELATIVELY POOR AGREEMENT. THIS IS
LIKELY DUE TO A DIFFERENCE IN MODEL TRACKS. HAFS-A SUGGESTS A STEEP 
DROP IN INTENSITY AFTER TAU 24 BECAUSE IT TRACKS THE SYSTEM OVER 
LAND. GFS HAS A PEAK INTENSITY OF 100 KTS AT TAU 12 AND HAS A MUCH 
MORE GRADUAL WEAKENING TREND BECAUSE IT DOESN'T TRACK THE SYSTEM OVER
LAND. THE JTWC INTENSITY FORECAST ATTAINS THE MIDDLE GROUND BETWEEN
THE TWO SCENARIOS AS THE JTWC FORECAST TRACKS THE SYSTEM ALONG THE
COAST, NOT AS INLAND AS HAFS-A. DUE TO SLIGHT DIFFERENCES IN TRACK
CAUSING A BIG CHANGE IN INTENSITY, THE JTWC INTENSITY FORECAST IS
ALSO ASSESSED WITH OVERALL LOW CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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