Typhoon 23W(NESAT): +35knots/24h, to peak within 36h//Invest 91W: TCFA issued but still subtropical//1609utc

JTWC IS ISSUING 6HOURLY SATELLITE BULLETINS ON 23W(NESAT). 3HOURLY SATELLITE BULLETINS ARE ISSUED ON 23W AND INVEST 91W.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: HAVING CLEARED THE CAPE BOJEADOR AND MOVED INTO OPEN WATERS, TY NESAT HAS RAPIDLY INTENSIFIED, INCREASING FROM 50 TO 70 KNOTS IN THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY AND ENHANCED INFRARED (EIR) IMAGERY SHOW THAT CLOUD TOP TEMPS THAT WERE APPROACHING -80C AT 1800Z HAVE NOW WARMED TO -57C, THE EYE PRESENT EARLIER HAS BECOME CLOUD-FILLED AND THE RAPIDLY INTENSIFICATION TREND APPEARS TO HAVE BEEN ARRESTED, AT LEAST FOR NOW. MSI REVEALS THE PRESENCE OF A CURVED ARC TO THE EAST OF THE SYSTEM WHICH INDICATES THAT WHILE ENVIRONMENTAL SHEAR IS CURRENTLY NEAR 20 KNOTS, PREVIOUS DEEP CONVECTIVE ACTIVITY TO THE EAST OF THE CORE GENERATED ENOUGH OUTFLOW TO PUSH BACK AGAINST THE SHEAR AND LED TO A LOCALIZED REDUCTION IN SHEAR, ALLOWING FOR THE CONVECTIVE CONSOLIDATION AROUND THE EYE AND THE RAPID INTENSIFICATION. VORTICAL HOT TOWERS CONTINUE TO FIRE, PARTICULARLY ALONG A CONVERGENCE LINE TO THE NORTH OF THE CENTER, AS WELL AS TO THE SOUTHWEST. IF THESE CONTINUE TO TRACK UPSHEAR, THEN ANOTHER ROUND OF INTENSIFICATION IS POSSIBLE. A 160505Z AMSR2 89GHZ MICROWAVE IMAGE REVEALED A RAGGED, 45NM WIDE UPPER-LEVEL EYE FEATURE, WHILE THE 36GHZ SHOWED A WELL-DEFINED 26NM EYE FEATURE WITH SOME WESTWARD TILT WITH HEIGHT. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE USING THE 36GHZ MICROWAVE EYE FEATURE. THE INITIAL INTENSITY IS ALSO ASSESSED WITH HIGH CONFIDENCE, ROUGHLY IN THE MIDDLE OF THE AGENCY FIXES, SUPPORTED BY CIMSS EXPERIMENTAL ESTIMATES BETWEEN 65-72 KNOTS AND A 71 KNOT WIND IN THE 160505Z AMSR2 WINDSPEED PRODUCT. THE OVERALL ENVIRONMENT REMAINS FAVORABLE, WITH THE LOCALIZED REDUCED SHEAR, MODERATE TO STRONG POLEWARD AND EQUATORWARD OUTFLOW AND WARM SSTS.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: THERE ARE NO MAJOR CHANGES IN TRACK FORECAST COMPARED TO THE PREVIOUS FORECAST. THE PRIMARY STEERING INFLUENCE FOR THE FIRST 24 HOURS REMAINS THE STR CENTERED EAST OF KYUSHU. THE STR IS BEING ERODED DUE TO THE APPROACH OF A DEEP TROUGH FROM THE WEST, INDUCING A WEAKNESS IN THE RIDGE OVER SOUTHEASTERN CHINA. HOWEVER THE BREAK IN THE RIDGE IS TOO FAR NORTH AND TOO WEAK TO PULL TY 23W TOO FAR NORTH AND THE SYSTEM WILL REACH AN INFLECTION POINT AND ITS MAXIMUM POLEWARD EXTENT BY TAU 12, BUT IS EXPECTED TO REMAIN SOUTH OF THE 20TH LATITUDE LINE. AFTER THIS POINT, A BUILDING RIDGE EXTENDING EAST FROM A STR CENTERED OVER NORTHEAST MYANMAR WILL ASSUME THE DOMINANT STEERING ROLE AND PUSH TY 23W ONTO A MORE SOUTHWESTWARD TRACK THROUGH TAU 72. THE RIDGE WILL SLIDE EAST TO A POSITION OVER TAIWAN BY TAU 72, AND TY 23W WILL TURN NORTHWESTWARD ALONG THE SOUTHWEST SIDE OF THIS RIDGE, MOVING INTO THE SOUTHERN GULF OF TONKIN BY TAU 120. AFTER THE RECENT BURST OF INTENSIFICATION, THE PACE SEEMS TO HAVE SLOWED, WITH THE WARMING CLOUD TOPS AND OBSCURATION OF THE EYE. BUT THE ENVIRONMENT REMAINS FAVORABLE FOR THE NEXT 24 TO 36 HOURS, AND IF THE FLARING CONVECTION CAN CONTINUE TO PUSH BACK AGAINST THE MODERATE SHEAR, THEN ANOTHER ROUND OF INTENSIFICATION IS LIKELY. THE FORECAST CALLS FOR THIS, WITH INTENSIFICATION UP TO 90 KNOTS BY TAU 24. THEREAFTER THE SHEAR VECTOR SHIFTS FROM EAST TO SOUTH AND INCREASES TO ABOVE 25 KNOTS, LEADING TO A SLOW BUT STEADY WEAKENING TREND AFTER TAU 36. LOW-LEVEL FLOW DISRUPTION DUE TO PROXIMITY TO HAINAN, COUPLED WITH DRY AIR ENTRAINMENT INTO THE CORE FROM THE WEST WILL QUICKEN THE PACE OF WEAKENING AFTER TAU 72 AND THE SYSTEM IS EXPECTED TO BE A WEAK TROPICAL DEPRESSION BY TAU 120.

MODEL DISCUSSION: TRACK GUIDANCE CONTINUES TO BE IN GOOD CROSS-TRACK AGREEMENT THROUGH THE FORECAST PERIOD, WITH SPREAD GRADUALLY INCREASING TO 85NM AT TAU 72 AND 135NM AT TAU 120. ALONG-TRACK SPREAD INCREASES SHARPLY AFTER TAU 72 TO OVER 300NM BY TAU 120, WITH THE GFS AND JGSM FAR OUTPACING THE MAJORITY OF THE TRACKERS, HAVING THE SYSTEM WELL INLAND WEST OF HANOI BY TAU 120, WHILE THE UKMET AND ECMWF ENSEMBLE MEANS LAG WELL BEHIND THE PACK, PLACING THE CENTER JUST NORTH OF DA NANG BY TAU 120. THE JTWC FORECAST LIES CLOSEST TO THE ECMWF TRACKER FOR THE DURATION OF THE FORECAST, A BIT NORTH OF AND SLIGHTLY FASTER THAN THE CONSENSUS MEAN. INTENSITY GUIDANCE IS A MIXED BAG WITH A VERY LARGE SPREAD AND PEAK INTENSITIES RANGING FROM 75 KNOTS TO 110 KNOTS. A QUAD OF RAPID INTENSIFICATION AIDS INCLUDING RIPA HAVE TRIGGERED WITH THIS RUN, WITH PEAKS BETWEEN 95-110 KNOTS. MEANWHILE THE REMAINDER OF THE CONSENSUS MEMBERS ARE BELOW 80 KNOTS. THE JTWC FORECAST IS ABOVE ALL OF THE GUIDANCE, TRACKING JUST SLIGHTLY LOWER THAN THE RI25 TREND LINE TO TAU 24, THEN LIES CLOSE TO THE HWRF, ON THE HIGH END OF THE GUIDANCE ENVELOPE THROUGH THE REMAINDER OF THE FORECAST.

THE AREA OF CONVECTION (INVEST 91W) PREVIOUSLY LOCATED NEAR 26.7N 153.4E IS NOW LOCATED NEAR 26.5N 153.4E, APPROXIMATELY 874 NM EAST-SOUTHEAST OF YOKOSUKA, JAPAN. THE SYSTEM IS CURRENTLY CLASSIFIED AS A SUBTROPICAL DEPRESSION, GENERALLY CHARACTERIZED AS HAVING BOTH TROPICAL AND MIDLATITUDE CYCLONE FEATURES. ANIMATED MULTISPECTRAL SATELLITE IMAGERY AND A 150245Z AMSR2 89 GHZ MICROWAVE DATA DEPICT A FULLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH EXPANSIVE CONVECTIVE BANDING DISPLACED ON THE WESTERN PERIPHERY. UPPER-LEVER ANALYSIS REVEALS A FAVORABLE ENVIRONMENT, WITH WARM (27-28C) SEA SURFACE TEMPERATURES, AND DECENT EQUATORWARD OUTFLOW; MAKING 91W A GREAT CANDIDATE FOR TRANSITIONING INTO A TROPICAL CYCLONE. GLOBAL MODELS ARE IN AGREEMENT THAT THE SYSTEM WILL LOSE JET SUPPORT, TAKE ON MORE TROPICAL CHARACTERISTICS AND INTENSIFY WHILE TRACKING EAST- NORTHEAST. FOR HAZARDS AND WARNINGS, REFERENCE THE FLEET WEATHER CENTER SAN DIEGO HIGH WINDS AND SEAS PRODUCT OR REFER TO LOCAL WMO DESIGNATED FORECAST AUTHORITY. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 30 TO 35 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1001 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS REMAINS HIGH. SEE REF B (WTPN21 PGTW 151930) FOR FURTHER DETAILS.

GLOBAL MODELS ARE IN AGREEMENT THAT THE SYSTEM WILL LOSE JET SUPPORT, TAKE ON MORE TROPICAL CHARACTERISTICS AND INTENSIFY WHILE TRACKING EAST- NORTHEAST.