WDPS31 PGTW 062100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 07P (SEVEN) WARNING NR 
001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.9S 153.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 734 NM WEST OF NOUMEA, NEW CALEDONIA
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A SMALL
SYSTEM, WHICH HAS RAPIDLY CONSOLIDATED AND DEVELOPED OVER THE
PREVIOUS 12 HOURS. EARLIER ASCAT DATA FROM THE 1200Z HOUR SUGGESTED
AN ELONGATED CIRCULATION WITH A SMALL CORE OF HIGHER WINDS
DEVELOPING IN THE SOUTHEAST END OF THE BROADER CIRCULATION.
ANIMATED EIR SINCE THAT TIME SHOWED HOT TOWERS FLARING UP NEAR
WHERE THE SCATTEROMETER SUGGESTED THE CENTER WOULD BE, AND THE
CONVECTION HAS CONTINUED TO CONSOLIDATE INTO A SYMMETRICAL BALL
THROUGH THE 1800Z HOUR. A 061729Z SSMIS 89GHZ MICROWAVE IMAGE
SHOWED STRONG CONVECTIVE BANDING FEATURES ON THE SOUTHERN SIDE OF
THE CIRCULATION WITH A NASCENT MID-LEVEL MICROWAVE EYE FEATURE. THE
INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON
EXTRAPOLATION OF THE EARLIER SCATTEROMETER DATA, AND THE
AFOREMENTIONED MICROWAVE IMAGERY. THE INITIAL INTENSITY IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON A DVORAK CURRENT INTENSITY ESTIMATE
OF T2.5 (35 KNOTS) FROM PGTW, SURFACE OBSERVATIONS FROM FREDERICK
REEF OF 35 KNOTS, A 061535Z AMSR2 WINDSPEED PRODUCT AND THE
STEADILY IMPROVING CONVECTIVE STRUCTURE. ANALYSIS REVEALS AN
UPPER-LEVEL POINT SOURCE DIRECTLY OVER THE LOW LEVEL CIRCULATION,
WHICH IS PROVIDING GOOD RADIAL OUTFLOW. AN UPPER-LEVEL TROUGH TO
THE SOUTH IS PROVIDING AN ENHANCED OUTFLOW CHANNEL TO POLEWARD AS
WELL. THE SYSTEM LIES IN A NARROW BELT OF LOW VWS WHICH EXTENDS
FROM THE EAST COAST OF AUSTRALIA TO NEW CALEDONIA. THE SYSTEM IS
MOVING QUICKLY SOUTHEASTWARD ALONG THE SOUTHWEST PERIPHERY OF A
DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST.

INITIAL WIND RADII BASIS: SCATTEROMETER AND AMSR2 DATA. 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T1.5 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: POLEWARD OUTFLOW CHANNEL INTO BASE OF UPPER-LEVEL
TROUGH. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

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

FORECAST DISCUSSION: ALREADY MOVING A FAIR CLIP, TC 07P IS FORECAST
TO CONTINUE TO ACCELERATE ON A STRAIGHT SOUTHEASTWARD TRACK THROUGH
THE FORECAST PERIOD AS THE STEERING RIDGE TO THE NORTHEAST
CONTINUES TO STRENGTHEN. A SLIGHT TURN TOWARDS THE SOUTH IS
EXPECTED BY THE END OF THE FORECAST PERIOD AS THE RIDGE BUILDS
STRONGLY POLEWARD. WHILE CONDITIONS ARE GENERALLY FAVORABLE AT
PRESENT, THIS HOLIDAY IS NOT EXPECTED TO LAST LONG. AS IT CONTINUES
TO TRACK SOUTHEASTWARD, THE SYSTEM IS EXPECTED TO LOSE THE
UPPER-LEVEL POINT SOURCE, AND MOVE UNDER THE SUBTROPICAL WESTERLIES
ASSOCIATED WITH THE STRONG TROUGH TO THE SOUTH. SHEAR IS EXPECTED
TO REMAIN RELATIVELY LOW HOWEVER, AT LEAST FOR THE NEXT 24 HOURS,
WHICH SHOULD ALLOW FOR SOME INTENSIFICATION UP TO ABOUT 40-45
KNOTS. AFTER TAU 24, THINGS GET A BIT COMPLICATED, WITH THE
RELIABLE GFS MODEL SHOWING THE SYSTEM STRETCHING OUT TOWARDS THE
SOUTHEAST, AND DEVELOPING A SECONDARY CIRCULATION CENTER, WHICH
THEN MERGES WITH AN EXISTING WEAK LOW PRESSURE AREA CURRENTLY
SITTING NORTHWEST OF NEW CALEDONIA. THIS MERGER ALLOWS FOR A BRIEF
PERIOD OF INTENSIFICATION AS THE SYSTEM PASSES NEW CALEDONIA. AT
THE SAME TIME, THE SYSTEM MOVES INTO WATERS LESS THAN 26C, AND
MOVES UNDER THE SUBTROPICAL JET, MARKING THE START OF SUBTROPICAL
TRANSITION (STT). STT IS EXPECTED TO BE COMPLETE NO LATER THAN TAU
72, AS THE SYSTEM BECOMES A GALE-FORCE SUBTROPICAL LOW PRESSURE AREA
NORTH OF NEW ZEALAND.  

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
GOOD AGREEMENT THROUGH THE DURATION OF THE FORECAST PERIOD.
HOWEVER, THE GFS DETERMINISTIC MODEL DEVELOPS A SECONDARY
CIRCULATION CENTER WHICH THE TRACKER JUMPS TO, WHILE LOSING THE
CURRENT VORTEX BY TAU 36 TO THE NORTHWEST OF NEW CALEDONIA. THE
REMAINDER OF THE CONSENSUS TRACKERS SUPPORT THE VORTEX TRACKING
STRAIGHT TO THE SOUTHEAST IN A RELATIVELY TIGHT ENVELOPE THROUGH
TAU 72. THE JTWC FORECAST IS CONSISTENT WITH THE BULK OF GUIDANCE
AND SLIGHTLY SOUTH AND FASTER THAN THE CONSENSUS MEAN, THOUGH
CONFIDENCE IS LOW DUE TO THE UNCERTAINTY SURROUNDING THE ULTIMATE
DISPOSITION OF THE LLCC AS IT SLIDES SOUTH OF NEW CALEDONIA.
INTENSITY GUIDANCE IS MIXED, WITH THE MESOSCALE MODELS SHOWING
SLIGHT DEPARTURES ABOVE AND BELOW A 35 KNOT MEAN WITH A PEAK OF 45
KNOTS IN THE HWRF. THE DECAY SHIPS MEANWHILE INDICATES A PEAK NEAR
90 KNOTS AT TAU 120, AFTER STEADY INTENSIFICATION THROUGH THE
ENTIRE PERIOD, WHICH IS CONSIDERED HIGHLY UNLIKELY. THE JTWC
FORECAST BASICALLY FOLLOWS THE MESOSCALE AVERAGE WITH LOW
CONFIDENCE. 

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