WDPS31 PGTW 290900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 06P (SIX) WARNING NR 
001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.3S 176.9E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 98 NM WEST-NORTHWEST OF SUVA, FIJI
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 06S (SIX) HAS TRANSFORMED AT AN INCREDIBLE
PACE FROM A 30 KNOT ILL-DEFINED CIRCULATION EMBEDDED WITH THE SPCZ,
TO A STRONG TROPICAL CYCLONE WITH A MICROWAVE AND RADAR EYE
FEATURE. POST-ANALYSIS SUGGESTS THAT THE 290000Z INTENSITY WAS
VERY LIKELY WELL ABOVE 35 KNOTS BUT A LACK OF DATA, THE VERY SMALL
NATURE OF THE SYSTEM AND THE OVERALL WEAK APPEARANCE IN VISIBLE AND
INFRARED SATELLITE IMAGERY PRECLUDED ASSESSING IT AT A HIGHER
INTENSITY AT THAT TIME. A 290158Z AMSR2 MICROWAVE PASS CHANGED ALL
THAT IN AN INSTANT, WHEN IT REVEALED A CLEAR, VERTICALLY ALIGNED
MICROWAVE EYE IN BOTH THE 89GHZ AND MOST STRIKINGLY IN THE COLOR
ENHANCED 36GHZ IMAGE. A QUICK GANDER AT THE RADAR DATA OUT OF NADI,
CONFIRMED THE SYMMETRIC AND ALIGNED NATURE OF THE VORTEX, WHICH
CONTINUED TO BECOME BETTER DEFINED. BASED ON THE RADAR DATA, THE
SYSTEM LIKELY REACHED PEAK INTENSITY AROUND 0400Z-0500Z. BY 290600Z
THE CENTER WAS PASSING VERY CLOSE TO WAYASEWA AND KUATA ISLAND,
MOVING EASTWARD AT ABOUT 14 KNOTS. THE RADAR DEPICTION HAS BECOME
INCREASINGLY RAGGED SINCE THE 0500Z PEAK. THE MSI AND ENHANCED
INFRARED (EIR) IMAGERY HAVE NEVER SHOWN A CLEAR EYE, THOUGH THERE
WAS BRIEFLY A WARM SPOT IN THE BD-ENHANCED EIR. THE INITIAL
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE RADAR EYE
FEATURE. THE INITIAL INTENSITY IS ASSESSED WITH LOW CONFIDENCE, AS
THE SMALL SIZE OF THE SYSTEM IS PRECLUDING ACCURATE DVORAK-BASED
INTENSITY ESTIMATES AND CIMSS OBJECTIVE ESTIMATES ARE NOT YET
AVAILABLE, MEANING THE INTENSITY ASSESSMENT IS BASED ALMOST
ENTIRELY ON THE APPEARANCE OF THE SYSTEM IN THE MICROWAVE IMAGERY.
THE ENVIRONMENT IS GENERALLY FAVORABLE, WITH WARM SSTS, LOW VWS AND
MODERATE POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: OTHER 

CURRENT STEERING MECHANISM: TC 06S IS EMBEDDED WITH A TROUGH
ASSOCIATED WITH THE SPCZ, AND WILL RIDE ALONG AND WITHIN THIS
TROUGH, WITH ADDITIONAL INFLUENCE FROM A DEEP-LAYER NEAR-EQUATORIAL
RIDGE (NER) TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T2.0 - 30 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: EXTREME SMALL SIZE OF THE SYSTEM. 

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TC 06S IS FORECAST TO TRACK GENERALLY
EASTWARD, WITHIN A LOW PRESSURE TROUGH WHICH LIES ON A GENERAL
WEST-EAST LINE FROM FIJI TO NIUE AND THEN SOUTHEAST TO THE COOK
ISLANDS. ADDITIONAL STEERING PRESSURE WILL BE APPLIED BY THE
DEEP-LAYER NER SITUATED TO THE NORTHEAST. THE SYSTEM WILL CLIP THE
NORTHERN COAST OF VITI LEVU OVER THE NEXT 12 HOURS, THEN TRACK
EASTWARD THROUGH THE NORTHERN PART OF THE LOMAIVITI GROUP AND THE
NORTHERN AND CENTRAL LAU GROUPS OF ISLANDS WITHIN THE FIRST 24
HOURS OF THE FORECAST. AFTER TAU 36 TC 06S IS FORECAST TO TURN MORE
SOUTHEASTWARD TOWARDS THE VAVA'U GROUP OF TONGA. THE EXTREMELY
SMALL SIZE OF TC 06S HAS ALLOWED IT TO THRIVE IN AN ENVIRONMENT
WHICH IN GENERAL WOULD NOT BE EXPECTED TO SUPPORT RAPID
INTENSIFICATION. UPPER-LEVEL WINDS ARE IN GENERAL FROM THE WEST,
BUT THE MOST RECENT CIMSS ATMOSPHERIC MOTION VECTOR (AMV) ANALYSIS
SUGGESTS A SPLIT IN THE FLOW, JUST UPSTREAM (WEST) OF THE CORE OF
TC 06S, SUGGESTING THAT THE LOCALIZED SHEAR DIRECTLY OVER TC 06S IS
ACTUALLY EVEN LOWER. AND WHILE OUTFLOW IS MOST PROMINENT TO THE
SOUTH, THE SPLIT FLOW HAS PROVIDED A BIT OF AN EQUATORWARD OUTFLOW
CHANNEL AS WELL. THE SYSTEM ALSO CURRENTLY SITS IN A SMALL POCKET
OF DEEP MOISTURE, THOUGH EXTREMELY DRY AIR IS LURKING JUST TO THE
SOUTH AND WEST. THESE CONDITIONS ARE NOT EXPECTED TO LAST MUCH
BEYOND THE NEXT 12 HOURS, WITH ALL AVAILABLE MODEL DATA SUGGESTING
AN INCREASE IN SHEAR AND A SHARP DRYING IN THE MID-LEVELS AS THE
SYSTEM MOVES EAST OF VITU LEVU. THE SYSTEM IS THUS EXPECTED TO
MAINTAIN INTENSITY AS IT SKIRTS ACROSS THE NORTHERN COAST OF VITU
LEVU, THEN BEGIN A STEADY WEAKENING TREND, DISSIPATING AS A
TROPICAL CYCLONE WITHIN 36 TO 48 HOURS. 

MODEL DISCUSSION: MODEL DATA IS EXTREMELY LIMITED, IN THE SENSE
THAT THE ONLY MODEL THAT HAS PICKED UP ON TC 06S IN ANY MEANINGFUL
WAY IS THE HWRF AND EVEN IT DID NOT INDICATE THE EXTREMELY RAPID
INTENSIFICATION SEEN OVER THE LAST 6 HOURS. HOWEVER, FROM A TRACK
PERSPECTIVE, THE GLOBAL MODELS DO IN GENERAL SEEM TO HAVE A GOOD
HANDLE ON THE SYSTEM TRACKING TOWARDS THE EAST THEN TURNING
SOUTHEAST BY TAU 48. THE GFS HOWEVER, LOSES THE VORTEX COMPLETELY,
NOT REALLY HAVING A VORTEX TO BEGIN WITH, WITHIN THE FIRST 12
HOURS. THE ECMWF, HAFS-A AND HWRF AND UKMET ARE IN STRONG AGREEMENT
WITH THE JTWC FORECAST TRACK, BUT CONFIDENCE REMAINS MEDIUM DUE TO
THE FACT THAT THE MODELS ARE NOT INITIALIZING WELL AND THUS OUTPUT
IS LIKELY QUESTIONABLE. IN TERMS OF INTENSITY, AS NOTED ABOVE, THE
ONLY MODEL THAT HAS SHOWN ANY SORT OF SKILL IN DEPICTING A
MODERATELY STRONG VORTEX IS HWRF. IN THE FORECAST, HWRF SHOWS THE
SYSTEM WEAKENING JUST AS RAPIDLY AS IT DEVELOPED, REACHING 30 KNOTS
WITHIN 12 HOURS. THE HAFS-A AND COAMPS-TC MEANWHILE WEAKEN THE
SYSTEM AT A SLOWER PACE. THE TRUTH LIKELY LIES SOMEWHERE BETWEEN,
AND THE JTWC FORECAST IS A BLEND OF THE DETERMINISTIC OUTCOMES,
THOUGH THE FORECAST IS HIGHER THAN THE GUIDANCE THROUGH TAU 24.
CONFIDENCE IS LOW IN ALL ASPECTS THROUGH THE FORECAST PERIOD. 

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