WDXS31 PGTW 122100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 17S (FILIPO) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.5S 33.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 379 NM WEST-SOUTHWEST OF EUROPA ISLAND
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: -- FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 17S (FILIPO) ROUNDING THE WESTERN PERIPHERY OF A
SUBTROPICAL RIDGE (STR) TO THE EAST AND SITUATED OVER LAND AS IT
APPROACHES THE SOUTHERN COAST OF MOZAMBIQUE. THE SYSTEM REMAINS
MOIST DESPITE BEING OVER LAND AND DRY AIR WRAPPING IN FROM THE
NORTHWEST OFF OF THE EASTERN AFRICAN CONTINENT. DESPITE WEAKENING
SIGNIFICANTLY WHILE OVER LAND OVER THE LAST 12 HOURS, SHEAR
CONDITIONS ARE FAVORABLE TO SUSTAIN THE VORTEX WITH LOW (10-15KT)
VERTICAL WIND SHEAR (VWS) AND MODERATE POLEWARD OUTFLOW. THE
INITIAL POSITION WAS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
ANIMATED EIR AND EXTRAPOLATION FROM A 121637Z IMAGE REVEALING A
LLCC AS THE SYSTEM WITH DEFLATING DEEP LAYER CONVECTION. THE
INITIAL INTENSITY WAS DETERMINED WITH LOW CONFIDENCE BASED ON
PERSISTENCE, AS WELL AS THE DPRINT AND DMINT ESTIMATES NOTED BELOW.
ADDITIONALLY, SURFACE OBSERVATIONS FROM XIA XIA, MOZAMBIQUE HAVE
BEEN SHOWING WINDS BETWEEN 20-33 KNOTS (10-MINUTE) OVER THE PAST
FEW HOURS AS THE SYSTEM APPROACHES FROM THE NORTH.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF AN STR TO THE
EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: LOW
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: TC 17S IS NOW ASSESSED TO BECOME
FULLY EXTRATROPICAL BETWEEN TAU 48 AND 72. 

FORECAST DISCUSSION: TC 17S IS FORECAST TO CONTINUE TO TRACK SOUTH
OVER THE NEXT 12 HOURS WHILE UNDERGOING A BRIEF SUBTROPICAL
TRANSITION (STT) BEFORE CONTINUING TO ROUND THE SOUTHWESTERN
PERIPHERY OF THE STR TO THE NORTHEAST, COMMENCING ITS EXTRATROPICAL
TRANSITION (ETT) BY TAU 36, WITH THE EXPECTATION OF FULL
EXTRATROPICAL TRANSITION NO LATER TAU 60. ONCE TC 17S MOVES BACK
OVER WATER IN THE NEXT FEW HOURS, IT IS ANTICIPATED THAT IT WILL
RAPIDLY RECONSOLIDATE STRONG VORTEX, AND RAPIDLY INTENSIFY OVER THE
NEXT 36 HOURS, TO A PEAK OF AT LEAST 65 KTS AS A JET MAXIMUM TO THE
SOUTH ENHANCES OUTFLOW SIGNIFICANTLY BETWEEN TAU 18-24. VWS
INCREASES TO APPROXIMATELY 40KTS AT TAU 36, SHEARING APART THE
VORTEX AND WEAKENING THE SYSTEM TO 50KTS BY THE COMPLETION OF ITS
EXTRATROPICAL TRANSITION AT TAU 60. THE SYSTEM IS ALSO ANTICIPATED
TO TRANSITION OVER COOL 25C SSTS AROUND TAU 60, FURTHER ENCOURAGING
ETT AND WEAKENING STORM INTENSITY. 

MODEL DISCUSSION: THE JTWC TRACK MODEL GUIDANCE IS IN STRONG
AGREEMENT THAT TC 17S WILL CONTINUE TO TRACK SOUTH AND THEN
SOUTHWEST THROUGH THE END OF THE FORECAST PERIOD. THE GUIDANCE IS
WELL-CONSTRAINED, WITH MINIMAL CROSS- OR ALONG-TRACK SPREAD,
LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST. THE JTWC
INTENSITY GUIDANCE SUGGESTS SOME VARIANCE IN THE PEAK OF THE
SYSTEM, WITH COAMPS-TC PEAKING AT 75KTS BY TAU 36 WHILE THE
CONSENSUS PEAKS AT 60KTS BY TAU 48. THE MODELS SEEM TO ASSESS
DIFFERENTING IMPACTS OF THE VWS AND THE POSITIVE OUTFLOW VALUES
SUPPORTED BY THE JET MAXIMUM TO THE SOUTH. THE INTENSITY WAS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON MODEL DISAGREEMENT IN HOW
SIGNIFICANTLY THE SYSTEM WILL INTENSIFY AS IT STRIKES A BALANCE
BETWEEN ELEVATED VWS AND FAVORABLE OUTFLOW. 

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