WDPS31 PGTW 070300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 07P (SEVEN) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.5S 155.1E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 622 NM WEST OF NOUMEA, NEW CALEDONIA
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 19 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN ELONGATED
CIRCULATION, STRETCHED OUT FROM SOUTHEAST TO NORTHWEST, WITH A
SMALL KERNEL OF A CIRCULATION IN THE FAR SOUTHEASTERN PORTION,
WHICH IS THE CORE OF TC 07P. THIS ASSESSMENT IS BASED ON ANALYSIS
OF THE ANIMATED MSI IN WHICH THE NORTHWESTERN SECTION OF THE
CIRCULATION HAS STARTED TO PEAK OUT FROM UNDER THE CONVECTIVE
BLOWOFF, COMBINED WITH A 062228Z ASCAT-B PARTIAL PASS WHICH SHOWED
THE SMALL LLCC TUCKED INTO THE SOUTHEAST CORNER OF THE BROADER
CIRCULATION. ENHANCED INFRARED (EIR) IMAGERY SHOWS HOT TOWERS WITH
TEMPERATURES BELOW -90C FIRING UP NEAR THE ASSESSED CENTER AND
GLOBAL LIGHTNING DATA SHOWS A STRONG INNER-CORE LIGHTNING BURST
COMMENCING AT 070000Z, SUGGESTIVE OF INTENSIFICATION. THE INITIAL
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON AN EXTRAPOLATION
OF THE ASCAT AMBIGUITY FIX AND THE PGTW POSITION FIX. THE INITIAL
INTENSITY IS UPPED A NOTCH TO 40 KNOTS WITH HIGH CONFIDENCE BASED
ON MULTIPLE FACTORS INCLUDING A 2000Z SHIP OBSERVATION OF 40 KNOTS,
A 061937Z SMAP PASS WITH 1-MIN WINDS OF 42 KNOTS, THE 062228Z ASCAT
SHOWING WINDS UP TO 38 KNOTS, ALONG WITH SUBJECTIVE AND OBJECTIVE
DVORAK BASED INTENSITY ESTIMATES BETWEEN T2.0 (30 KNOTS) AND T3.0
(45 KNOTS). THE ENVIRONMENT, WHILE NOT OPTIMAL, IS CLEARLY
SUPPORTIVE OF DEVELOPMENT FOR THE TIME BEING, WITH LOW VWS, WARM
SSTS AND STRONG POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: SCATTEROMETER AND SMAP 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: T2.0 - 30 KTS
   CIMSS ADT: 45 KTS AT 062330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD
   OTHER FACTORS: MODERATE EQUATORWARD OUTFLOW

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING. HOWEVER, THE FORECAST HAS
BEEN TRUNCATED TO 48 HOURS DUE TO AN ACCELERATED TIMELINE FOR
SUBTROPICAL TRANSITION. 

FORECAST DISCUSSION: TC 07P (SEVEN) HAS CONTINUED TO TRANSIT
RAPIDLY TOWARDS THE SOUTHEAST ALONG THE SOUTHWESTERN SIDE OF A DEEP
STR CENTERED FAR TO THE NORTHEAST. NO MAJOR CHANGES ARE EXPECTED IN
THE GENERAL TRACK MOTION, OTHER THAN SOME FURTHER ACCELERATION
THROUGH THE FORECAST PERIOD AS THE STR BUILDS AND STRENGTHENS THE
STEERING GRADIENT. IT REMAINS POSSIBLE THAT THE SYSTEM COULD EVOLVE
INTO MORE THAN ONE CENTER OF CIRCULATION, WITH ONE SPINNING OUT OF
THE NORTHWESTERN END OF THE ELONGATED CIRCULATION AND MOVING EAST
OVER NORTHERN NEW CALEDONIA, WHILE THE CURRENT LLCC CONTINUES TO
TRACK SOUTHEASTWARD. THIS SCENARIO IS DEPICTED WELL IN THE GFS
DETERMINISTIC RUN WHILE THE REMAINDER OF THE MODELS SHOW ONE
CIRCULATION TRACKING SOUTHEASTWARD. REGARDLESS, THE FORECAST TRACKS
TWO PRIMARY CIRCULATION THROUGHOUT THE FORECAST PERIOD. OVER THE
SHORT-TERM, ADDITIONAL INTENSIFICATION IS LIKELY, AS THE SYSTEM
WILL REMAIN OVER WARM WATERS AND WILL CONTINUE TO TAP INTO STRONG
POLEWARD OUTFLOW, WHILE SHEAR REMAINS RELATIVELY LOW. THE RECENT
INNER-CORE LIGHTNING BURST IS SUGGESTIVE OF THE INTENSIFICATION
TREND AND THE FORECAST CALLS FOR THE TO PEAK AT 45-50 KNOTS BY TAU
12. THEREAFTER TC 07P WILL START TO SLOWLY WEAKEN AS IT STARTS TO
FEEL THE IMPACTS OF SHARPLY INCREASING VWS AND IS STEADILY ENGULFED
BY A DRY MID-LEVEL AIR MASS. BY AROUND TAU 24 THE SYSTEM WILL MOVE
SOUTH OF THE 26C ISOTHERM AND MOVE UNDER THE SUBTROPICAL WESTERLIES
ALOFT, MARKING THE BEGINNING OF SUBTROPICAL TRANSITION (STT). BY
TAU 48 THE SYSTEM WILL LIKELY MERGE WITH INVEST 95P, CURRENTLY
DRIFTING SOUTH TO THE EAST OF NEW CALEDONIA, WHILE BECOMING FULLY
EMBEDDED UNDER THE SUBTROPICAL WESTERLIES ALOFT AND MOVING OVER
COOLER WATERS. TRANSITION TO A FULLY SUBTROPICAL LOW IS EXPECTED TO
BE COMPLETE NO LATER THAN TAU 48. WHILE THE SYSTEM IS EXPECTED TO
WEAKEN BELOW THE 35 KNOT WARNING THRESHOLD BY TAU 48, AN ADDITIONAL
ROUND OF INTENSIFICATION IS POSSIBLE IN THE LATER TAUS, AFTER THE
CURRENT FORECAST PERIOD, DUE TO STRONG BAROCLINIC FORCING AS THE
SYSTEM TURNS SOUTH AND BECOMES EXTRATROPICAL. 

MODEL DISCUSSION: THE DYNAMIC MODEL GUIDANCE PACKAGE IS IN OVERALL
GOOD AGREEMENT THROUGH THE FORECAST PERIOD, WITH THE CONTINUED
EXCEPTION OF THE GFS DETERMINISTIC TRACKER, WHICH IS PERSISTENT IN
KILLING OFF THE VORTEX WITHIN THE FIRST 24 HOURS OF THE FORECAST.
AS MENTIONED ABOVE, THE GFS DETERMINISTIC RUN IS TRACKING A
SECONDARY CIRCULATION CENTER WHICH SPLITS OFF FROM THE PRIMARY
CIRCULATION. THE REMAINDER OF THE TRACKERS ARE CONSTRAINED TO A
TIGHT ENVELOPE MOVING SOUTHEAST THROUGH THE FORECAST PERIOD,
LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK, WHICH LIES ON
THE NORTHERN EDGE OF THE GUIDANCE ENVELOPE. INTENSITY GUIDANCE
REMAINS MIXED, WITH THE DECAY-SHIPS (GFS) SHOWING A PEAK INTENSITY
NEAR 80 KNOTS, BY THE END OF THE RUN, EVEN THOUGH IT LOSES THE
VORTEX BY TAU 36, AND THUS IS DISCARDED AS UNRELIABLE. THE
MESOSCALE MODELS INCLUDING HWRF AND COAMPS-TC SHOW SOME MARGINAL
INTENSIFICATION IN THE NEAR-TERM FOLLOWED BY RAPID WEAKENING
THEREAFTER. THE JTWC FORECAST CLOSELY TRACKS THE HWRF SOLUTION,
WITH MEDIUM CONFIDENCE. 

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