WDXS31 PGTW 180300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 11S (FREDDY) WARNING 
NR 031//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.1S 71.5E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 543 NM SOUTH OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
RAPIDLY DETERIORATING INNER CORE AND SHRINKING EYE, DOWN TO
APPROXIMATELY 13NM AT ANALYSIS TIME AND SHRINKING FURTHER THROUGH
THE 0200Z HOUR. THE PREVIOUSLY VERY WELL-DEFINED CENTRAL DENSE
OVERCAST (CDO) HAS ERODED SIGNIFICANTLY ON THE EASTERN SIDE AND THE
LATEST BD ENHANCED EIR SUGGESTS THE EYEWALL MAY HAVE BROKEN ON THE
EAST SIDE OF THE SYSTEM. CIMSS ANALYSIS REVEALS AN UPPER-LEVEL
POINT SOURCE AND RELATIVELY LOW SHEAR IN THE RANGE OF 10-15 KNOTS.
HOWEVER, HIGH-RESOLUTION GFS AND HWRF CROSS SECTIONS AND SOUNDINGS
INDICATE THE PRESENCE OF MODERATE (UP TO 20 KTS) EASTERLY SHEAR IN
THE MID-LEVELS, BELOW THE CIRRUS CANOPY. ADDITIONALLY, THE MODEL
CROSS-SECTIONS AND CIRA ADVECTED LAYER PRECIPITABLE WATER PRODUCT
INDICATE DRY MID-LEVEL AIR WRAPPING AROUND THE WESTERN THROUGH
NORTHERN PORTION OF THE CORE, ENCROACHING ON THE CENTER ON THE EAST
SIDE AND INDUCING SOME DOWNWARD VERTICAL MOTION, CONTRIBUTING TO
THE EROSION OF THE EASTERN EYEWALL. THE INITIAL POSITION IS
ASSESSED WITH HIGH CONFIDENCE ON THE 13NM EYE IN THE EIR. THE
INITIAL INTENSITY IS HEDGED SLIGHTLY LOWER THAN THE AGENCY CURRENT
INTENSITY ESTIMATES OF T6.5 (127 KTS) BASED ON THE LOWER FINAL-T
NUMBERS, MOSTLY IN THE T6.0 (115 KTS) RANGE, AND THE SATCON
ESTIMATE.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   KNES: T6.5 - 127 KTS
   FMEE: T6.5 - 127 KTS
   FIMP: T6.5 - 127 KTS
   CIMSS SATCON: 116 KTS AT 172046Z
   CIMSS ADT: 122 KTS AT 180000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: DRY MID-LEVEL AIR WRAPPING AROUND THE SYSTEM AND
ENCROACHING ON THE INNER CORE. 

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: TC 11S (FREDDY) HAS TRACKED ALMOST DUE
WESTWARD OVER THE PAST 12 HOURS, ALONG THE NORTH SIDE OF A DEEP STR
TO THE SOUTH. IT IS ANTICIPATED THAT A WEAK UPPER-LEVEL TROUGH FAR
TO THE SOUTH WILL RAPIDLY TRANSLATE EASTWARD OVER THE NEXT 24
HOURS, AND WHILE THIS WILL INDUCE A BREAK IN THE STR, THE IMPACT IS
NOT EXPECTED TO BE FELT FAR ENOUGH NORTH TO MAKE MUCH OF A
DIFFERENCE IN THE TRACK OF TC 11S. THE SYSTEM WILL TURN OVER
TOWARDS A MORE SOUTHWESTWARD TRACK AFTER TAU 24 BUT NO SIGNIFICANT
COURSE CHANGES ARE ANTICIPATED THROUGH TAU 96. THE SYSTEM SHOULD
PASS ABOUT 100NM-125NM TO THE NORTH OF BOTH MAURITIUS AND LA REUNION
BY TAU 72. LANDFALL ALONG THE CENTRAL COAST OF MADAGASCAR IS
EXPECTED SLIGHTLY BEFORE TAU 96, AND THE SYSTEM IS FORECAST TO
CROSS OVER THE CENTRAL PORTION OF ISLAND AND REEMERGE OVER THE
MOZAMBIQUE CHANNEL BY TAU 120. THE INTENSITY FORECAST CONTINUES TO
BE THE MORE CHALLENGING ASPECT OF TC 11S. TO DATE THERE HAS BEEN NO
INDICATION OF AN EYEWALL REPLACEMENT CYCLE (EWRC), BUT THE LACK OF
RECENT MICROWAVE IMAGERY PRECLUDES A DEFINITIVE ANALYSIS. HOWEVER,
THE CIMSS M-PERC FORECAST CONTINUES TO INDICATE A LOW PROBABILITY
OF EWRC GOING FORWARD. AS NOTED, THE DRY MID-LEVEL AIR
PENETRATION, AND MODEST BELOW OUTFLOW-LAYER EASTERLY SHEAR ARE
THE MOST LIKELY CANDIDATES FOR THE RECENT WEAKENING SEEN OVER THE
PAST 12 HOURS. THESE FEATURES ARE EXPECTED TO STICK AROUND FOR THE
NEXT DAY OR SO. AFTER TAU 24, MODELS ARE SUGGESTING A WEAKENING OF
THE SHEAR GRADIENT AND MODEST MOISTENING OF THE LOW TO MID-LEVELS,
WHILE THE SYSTEM WILL ALSO BE MOVING OVER SOME SLIGHTLY MORE
FAVORABLE OHC CONDITIONS, WHICH SHOULD ALLOW FOR A MODERATE AMOUNT
OF INTENSIFICATION THROUGH TAU 48. WHILE SHEAR IS EXPECTED TO REMAIN
LOW THROUGH THE REMAINDER OF THE FORECAST, THE COMBINATION OF
CONVERGENT FLOW ALOFT, A DRAMATICALLY ENLARGING EYE AND STEADILY
LOWERING OHC AND SST VALUES, WILL SLOWLY BUT STEADILY WEAKEN THE
SYSTEM AS IT APPROACHES MADAGASCAR. AS THE SYSTEM CROSSES
MADAGASCAR IT WILL RAPIDLY WEAKEN DOWN TO NEAR 40 KNOTS. HOWEVER,
THE SYSTEM MOVES BACK INTO A FAVORABLE ENVIRONMENT ONCE IN THE
MOZAMBIQUE CHANNEL, AND REINTENSIFICATION IS EXPECTED TO BEGIN
SHORTLY AFTER TAU 120. 

MODEL DISCUSSION: ALL MEMBERS OF THE CONSENSUS ARE IN GOOD
AGREEMENT ON THE WEST-SOUTHWEST TRACK, WITH THE DETERMINISTIC
GUIDANCE WELL CONSTRAINED IN A GRADUALLY EXPANDING ENVELOPE WHICH
REACHES 145NM AT TAU 72, AND MARGINALLY INCREASES TO 215NM THROUGH
TAU 120. ENSEMBLE MODELS ARE ALSO IN GOOD AGREEMENT, THOUGH
INDICATE SLIGHTLY MORE SPREAD PRIOR TO REACH MADAGASCAR. THE JTWC
FORECAST LIES SLIGHTLY NORTH OF THE CONSENSUS MEAN, CLOSELY
TRACKING THE ECMWF THROUGH THE BULK OF THE FORECAST. INTENSITY
GUIDANCE IS IN GOOD AGREEMENT AS WELL, WITH ALL BUT THE GFS SHOWING
A SLIGHT WEAKENING THROUGH THE FIRST 24 HOURS, FOLLOWED BY MARGINAL
REINTENSIFCATION AND THEN MORE SUBSTANTIAL WEAKENING THROUGH
LANDFALL. THE JTWC FORECAST IGNORES THE GFS WHICH IS DRAMATICALLY
WEAKER THAN THE OTHER MODELS AND LIES SLIGHTLY ABOVE THE CONSENSUS
MEAN THROUGH THE FORECAST PERIOD. 

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