TC 07P on the map,subtropical transition forecast by 48h//Invest 95P//0706utc

JTWC IS ISSUING 6HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TC 07P.

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.

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.