WDPS31 PGTW 291500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 06P (SIX) 
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.4S 177.9E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 51 NM NORTHWEST OF SUVA, FIJI
   MOVEMENT PAST 6 HOURS: EASTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 06S (SIX) IS LIKE THE SUPERNOVA WHICH FLASHES
BRILLIANTLY IN AN INSTANT, ONLY TO JUST AS QUICKLY FADE AWAY.
HAVING DEVELOPED A MICROWAVE AND RADAR EYE WITHIN THE SPAN OF A FEW
HOURS EARLIER TODAY, THE SYSTEM HAS NOW RAPIDLY SHEARED APART AS IT
MOVES ALONG THE NORTHERN SHORE OF VITU LEVU. ANIMATED SHORTWAVE
INFRARED (SWIR) AND PROXY VISIBLE (PROXYVIS) SATELLITE IMAGERY
DEPICTS A FULLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC)
SITUATED RIGHT ON THE NORTHERN COAST OF VITU LEVU, NEAR TAVUA BAY.
THE SYSTEM HAS EVIDENTLY SUCCUMBED TO THE EFFECT OF THE ALBEIT
RELATIVELY LIGHT DEEP-LAYER SHEAR, DUE TO THE SHALLOWNESS OF THE
VORTEX AND THE PRESENCE OF SOME MODERATE SOUTHWESTERLY SHEAR AS
INDICATED IN BOTH THE NADI 291100Z SOUNDING AND MODEL-DERIVED
SOUNDINGS. THE NADI SOUNDING ALSO SHOWS THE VORTEX IS CAPPED AT
700MB BY A WEDGE OF DRY AIR ABOVE THAT LEVEL. THE VORTEX IS JUST
COMING OUT OF THE TERRAIN MASKING AREA AND THE NAUSORI RADAR IS
STARTING TO PICK UP ON A POSSIBLE ROTATION MOVING OVER THE
NORTHEASTERN PORTION OF VITU LEVU. THE INITIAL POSITION IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE ANIMATED PROXYVIS. THE INITIAL
INTENSITY IS ASSESSED WITH LOW CONFIDENCE DUE TO A LACK OF OVER
WATER FIXES AND OBJECTIVE ESTIMATES. AN EARLIER ASCAT PASS FROM
290928Z SHOWED A WELL-DEFINED BUT VERY SMALL LLCC, THOUGH MAXIMUM
WINDS WERE JUST 28 KNOTS. THE ENVIRONMENT HAS DETERIORATED AND IS
NOW MARGINAL AT BEST, WITH WARM SSTS AND GOOD DIVERGENT OUTFLOW
OFFSET BY INCREASING DRY AIR ENCROACHMENT AND MODERATE MID-LEVEL
SHEAR.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: TROPICAL CYCLONE (TC) 06S IS TRACKING
EASTWARD WITHIN A TROUGH THAT EXTENDS FROM FIJI EASTWARD TO NIUE
AND THEN SOUTHEASTWARD TO THE COOK ISLANDS. ADDITIONALLY, A
DEEP-LAYER NEAR EQUATORIAL RIDGE (NER) IS SITUATED TO THE
NORTHEAST, PROVIDING ADDITIONAL STEERING PRESSURE. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 47 KTS AT 291030Z
   CIMSS AIDT: 41 KTS AT 291030Z
   CIMSS D-PRINT: 29 KTS AT 291230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: SIGNIFICANT DRY MID-LEVEL AIR ENCROACHING FROM THE
WEST. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: LOW
   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 06S IS FORECAST TO CONTINUE TRACKING
TOWARDS THE EAST OVER THE NEXT 12 TO 24 HOURS, GENERALLY RIDING
ALONG THE SOUTHWESTERN SIDE OF THE DEEP NER AND WITHIN THE TROUGH
OF LOW PRESSURE ASSOCIATED WITH THE SPCZ. THE SYSTEM WILL CLIP THE
NORTHERN AND NORTHEASTERN COASTLINE OF VITU LEVU OVER THE NEXT FEW
HOURS, WITH THE COASTAL REGION LIKELY EXPERIENCING THE STRONGEST
WINDS WITHIN THE CORE OF THE SYSTEM. THE VORTEX WILL MOVE BACK OVER
WATER WITHIN THE NEXT FEW HOURS, THEN MOVE ACROSS THE NORTHERN
PORTION OF THE LOMAIVITI GROUP OF ISLANDS WITHIN THE NEXT 12 HOURS.
BY TAU 24, THE SYSTEM WILL CONTINUE TRACKING EASTWARD, CROSSING
THROUGH THE NORTHERN LAU GROUP OF ISLANDS BEFORE TURNING MORE
SOUTHEASTWARD BY TAU 36. IN TERMS OF INTENSITY, THE SYSTEM HAS
CLEARLY WEAKENED RAPIDLY OVER THE LAST SIX HOURS AS IT HAS BECOME
INCREASINGLY ENGULFED BY DRY MID-LEVEL AIR AND IS IMPACTED BY
MODERATE MID-LEVEL SHEAR. IN THE NEXT 12 HOURS, THE SYSTEM IS
EXPECTED TO MAINTAIN INTENSITY AS IT MOVES BACK OVER WATER AND
MOVES AWAY FROM THE DISRUPTIVE EFFECTS OF RUGGED ISLAND TERRAIN.
HWRF MODEL CROSS-SECTIONS DEPICT WELL THE ANTICIPATED SHALLOWING OF
THE VORTEX AS DRY AIR MOVES IN FROM THE WEST TO COMPLETELY ENGULF
THE SYSTEM AFTER TAU 12. BY TAU 24, THE VORTEX IS EXPECTED TO
EXTEND VERTICALLY TO JUST 850MB, AND DEVOID OF ANY AND ALL
CONVECTIVE ACTIVITY. THUS, THE FORECAST CALLS FOR FAIRLY RAPID
WEAKENING AFTER TAU 12, WITH THE SYSTEM EXPECTED TO DISSIPATE AS A
TROPICAL CYCLONE NO LATER THAN TAU 36.  

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT,
WITH ALL MODELS INDICATING AN EASTWARD TRACK TO TAU 24, AND A
GRADUAL TURN SOUTHEASTWARD BY THE END OF THE FORECAST PERIOD. THE
JTWC FORECAST LIES CLOSE TO THE MULTI-MODEL CONSENSUS MEAN WITH
MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT,
WITH THE JTWC FORECAST MOST CLOSELY TRACING THE COAMPS-TC INTENSITY
TREND, WITH HWRF AND HAFS-A WEAKENING THE SYSTEM SLIGHTLY FASTER,
WHILE THE SHIPS (GFS) WEAKENS THE SYSTEM MORE SLOWLY.

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