WDXS31 PGTW 311500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 11S (ELEVEN) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.9S 65.6E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 510 NM EAST-NORTHEAST OF PORT LOUIS,
MAURITIUS
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 11S (ELEVEN) CONTINUES TO STRUGGLE AGAINST
PERSISTENT, DEEP EASTERLY SHEAR WHILE MOVING ERRATICALLY OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) OVER
THE PAST 12 HOURS SHOWS THE SYSTEM SLIDING WEST-NORTHWESTWARD AT A
LEISURELY PACE THROUGH 310600Z HOUR, THEN SUDDENLY MAKING A SHARP
LEFT TURN AND ACCELERATING TOWARDS THE SOUTHWEST. THE CAUSE OF THIS
ERRATIC MOTION SHIFT IS LIKELY THE LOWERING OF THE STEERING LEVEL
AS THE VORTEX SHALLOWED OUT AFTER LOSING THE CONVECTIVE STRUCTURE
SEEN DURING THE OVERNIGHT HOURS. CURRENT IMAGERY SHOWS AN EXPOSED
LOW LEVEL CIRCULATION CENTER (LLCC) WITH DISORGANIZED CONVECTION
DISPLACED WELL TO THE WEST OF THE CENTER. A 311133Z SSMIS 91GHZ
IMAGE SHOWED WELL-DEFINED SHALLOW BANDING FEATURES ARRAYED IN A
HIGHLY SYMMETRICAL FASHION AROUND THE LLCC. THE INITIAL POSITION IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC AND THE
MICROWAVE IMAGE NOTED ABOVE. THE INITIAL INTENSITY IS ASSESSED WITH
MEDIUM CONFIDENCE, WITH THE SYSTEM RIGHT ON THE CUSP OF THE 35 KNOT
WARNING THRESHOLD BASED ON THE OBJECTIVE INTENSITY ESTIMATES NOTED
ABOVE. THE ENVIRONMENT IS MARGINAL TO MARGINALLY UNFAVORABLE, WITH
WARM SSTS AND WEAK WESTWARD OUTFLOW OFFSET BY MODERATE TO HIGH
EASTERLY WIND SHEAR.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE SOUTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS
   DEMS: T2.0 - 30 KTS
   FMEE: T2.0 - 30 KTS
   CIMSS SATCON: 41 KTS AT 31100Z
   CIMSS ADT: 35 KTS AT 311200Z
   CIMSS AIDT: 35 KTS AT 311200Z
   CIMSS D-MINT: 31 KTS AT 311213Z
   CIMSS D-PRINT: 28 KTS AT 311200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK WESTWARD
   OTHER FACTORS: DRYNESS IN THE MID-LEVELS. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: HAVING SHIFTED TRACK TOWARDS THE SOUTHWEST
AFTER 0600Z, TC 11S IS ALREADY BEGINNING TO LEVEL OUT ON A
WEST-SOUTHWEST TRACK, AS A BUILDING STR SOUTH OF THE MASCARENES
PUSHES EAST, PRESENTING THE NORTHWESTERN PERIPHERY OF THE RIDGE AS
THE PRIMARY STEERING INFLUENCE. TC 11S WILL CONTINUE ON THIS
WEST-SOUTHWESTWARD TRACK THROUGH TAU 72, WHEN IT WILL PASS NORTH OF
MAURITIUS. AFTER TAU 72, A SECOND STR WILL BUILD EASTWARD FROM
SOUTH AFRICA AND ASSUME THE DOMINANT STEERING ROLE, ALLOWING THE
TRACK OF TC 11S TO FLATTEN OUT THEN TURN MORE WEST-NORTHWEST AFTER
TAU 96. LANDFALL ALONG THE NORTHEASTERN COAST OF MADAGASCAR IN THE
VICINITY OF TOAMASINA IS EXPECTED AROUND TAU 96, WITH THE SYSTEM
MOVING FURTHER INLAND THROUGH THE REMAINDER OF THE FORECAST. IN
TERMS OF INTENSITY, IN A SIMILAR FASHION TO THE LAST COUPLE OF
FORECASTS, THE SYSTEM IS EXPECTED TO REMAIN STEADY STATE FOR THE
NEXT 48 HOURS AS IT CONTINUES TO FACE MODERATE TO STRONG EASTERLY
SHEAR BUT GETS A BOOST DURING DIURNAL CONVECTIVE MAXIMUMS, FOLLOWED
BY WEAKENING AS THE CONVECTION BLOWS OFF. GLOBAL AND MESOSCALE
MODELS CONCUR THAT THE ENVIRONMENTAL SHEAR WILL START TO WEAKEN
AROUND 36 HOURS FROM NOW, AND AT THE SAME TIME THE ENVIRONMENT IS
EXPECTED TO MOISTEN AND THE SYSTEM WILL MOVE OVER SLIGHTLY WARMER
WATERS. THESE POSITIVE FACTORS WILL ENABLE A PERIOD OF
INTENSIFICATION, WITH THE SYSTEM EXPECTED TO PEAK AT OR ABOVE 50
KNOTS AS IT APPROACHES LANDFALL. THE ACTUAL PEAK IN THE MODEL
GUIDANCE OCCURS BETWEEN THE TAU 72 AND TAU 96 FORECAST POINTS AND
IS NOT REFLECTED IN THE OFFICIAL FORECAST. AFTER LANDFALL, THE
SYSTEM WILL RAPIDLY WEAKEN AND DISSIPATE OVER THE RUGGED TERRAIN OF
CENTRAL MADAGASCAR. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE AGREEMENT HAS
STEADILY IMPROVED OVER THE LAST 24 HOURS, WITH THE PREVIOUSLY
ERRANT MODELS (UKMET AND MOGREPS) NOW REJOINING THE REMAINDER OF
THE CONSENSUS MEMBERS IN DEPICTING A SOUTHWEST TRACK, TURNING WEST
AND THEN WEST-NORTHWEST. WHILE ALL THE MODELS AGREE ON THE GENERAL
TRACK SCENARIO, THERE REMAINS A 300NM CROSS-TRACK SPREAD AT TAU
120, BUT MORE SIGNIFICANTLY ALONG-TRACK SPREAD INCREASES SHARPLY
AFTER TAU 72 TO OVER 500NM BETWEEN THE NAVGEM TO THE EAST AND ECMWF
TO THE WEST. THE JTWC FORECAST IS CONSISTENT WITH THE GFS MODEL AND
JUST NORTH OF THE CONSENSUS MEAN. THE BULK OF THE INTENSITY
GUIDANCE IS CONSISTENT WITH THE JTWC FORECAST, THOUGH THE HAFS-A
AND MESOSCALE GFS ARE NOTABLE OUTLIERS, WEAKENING AND DISSIPATING
THE SYSTEM WITHIN 24 HOURS. THE REMAINDER OF THE GUIDANCE PACKAGE
SHOWS A STEADY STATE INTENSITY THROUGH TAU 48, THEN RAMPS UP TO A
PEAK BETWEEN 50-60 KNOTS PRIOR TO LANDFALL FOLLOWED BY RAPID
WEAKENING OVER LAND. THE JTWC FORECAST IS CLOSE TO THE MULTIMODEL
CONSENSUS MEAN. 

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