Western Pacific: 19W(CHANTHU) intensity is forecast to peak near Typhoon level//Atlantic: 2 Tropical Cyclone Formation Alerts,16/09utc

16/00UTC.

TS 19W(CHANTHU). WARNING 41 ISSUED AT 16/09UTC.SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. HOWEVER, THE CURRENT FORECAST INCLUDES THE POTENTIAL OF AN ALTERNATE SCENARIO. FORECAST DISCUSSION: HAVING NOW BEGUN ITS TRACK TOWARDS THE NORTHEAST, TS 19W IS FORECAST TO CONTINUE ACCELERATING NORTHEASTWARD, TURNING MORE EASTWARD THROUGH THE DURATION OF THE FORECAST, AHEAD OF AN APPROACHING MID-LATITUDE TROUGH AND ALONG THE NORTHERN PERIPHERY OF THE DEEP SUBTROPICAL RIDGE TO THE SOUTHEAST. THE SYSTEM IS EXPECTED TO MAKE LANDFALL ALONG THE NORTHWESTERN COAST OF KYUSHU NEAR 24H, TRACK OVER THE INLAND SEA AND CROSS JUST SOUTH OF TOKYO BETWEEN 48H AND 60H. THERE REMAINS A SHORT WINDOW OF OPPORTUNITY FOR INTENSIFICATION OVER THE NEXT 12-18 HOURS AS THE VERTICAL WIND SHEAR(VWS) REMAINS RELATIVELY LOW WHILE AT THE SAME TIME THE SYSTEM CONTINUES TO TAP INTO ROBUST POLEWARD OUTFLOW. GOING INTO THE DIURNAL MAXIMUM THIS EVENING, THE SYSTEM SHOULD INTENSIFY UP TO 60 KNOTS BY 12H. ONCE OVER LAND AND TRAVERSING THE INLAND SEA, THE SYSTEM IS EXPECTED TO STEADILY WEAKEN DUE TO INCREASING VWS AND TERRAIN INTERACTION. AS TS 19W MAKES LANDFALL IT IS EXPECTED TO BEGIN INTERACTING WITH A WEAK BAROCLINIC ZONE CURRENTLY LYING ACROSS SOUTHERN KOREA AND JAPAN, AND BEGIN TO EXTRA-TROPICAL TRANSITION (ETT). AS THE SYSTEM COMPLETES ETT, THE WIND FIELD IS FORECAST TO INCREASE AND BECOME INCREASINGLY ASYMMETRIC, WHILE THE LLCC WILL BROADEN OUT AND DEEP CONVECTION WILL RAPIDLY DECAY. THE SYSTEM IS EXPECTED TO COMPLETE ETT BY 48H AS A GALE-FORCE LOW AS IT TRANSITS THE SOUTHERN COAST OF HONSHU. THERE ALSO EXISTS THE POTENTIAL FOR AN ALTERNATE SCENARIO BASED ON THE LATEST GLOBAL MODEL FIELDS, MANY OF WHICH NOW INDICATE A SIGNIFICANTLY WEAKER SYSTEM UNDERGOING ETT WHILE MOVING WELL SOUTH OF TOKYO AND BECOMING QUASI-STATIONARY TO THE SOUTH-SOUTHEAST OF TOKYO. IN THIS SCENARIO THE VORTICITY ASSOCIATED WITH TS 19W SPLITS AFTER LANDFALL, WITH AN AREA MOVING TO THE NORTH OF HONSHU AND BECOMING EXTRA-TROPICAL, WHILE THE REMAINDER TRACKS THROUGH THE INLAND SEA AND REMAINS TROPICAL. THE REMNANTS OF THIS AREA OF VORTICITY THEN TRACK SOUTH OF TOKYO, BUT LACKING DEEP CORE OF CONVECTION, DOES NOT STRONGLY INTERACT WITH THE MID-LATITUDE TROUGH TO THE NORTH, AND THUS SIMULTANEOUSLY DISSIPATES WHILE COMPLETING ETT.

TS 19W(CHANTHU). SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL STORM 19W APPEARS TO HAVE FINALLY STARTED ITS LONG-AWAITED TRACK TOWARDS THE NORTHEAST. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A VERY WELL DEFINED SWIRL OF LOW-LEVEL CLOUD BANDS WRAPPING INTO A LOW-LEVEL CIRCULATION CENTER (LLCC) OBSCURED BY FLARING CONVECTION EXTENDING SOUTHWARD FROM THE ASSESSED CENTER POSITION. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE ANIMATED VISIBLE IMAGERY, AND WITHIN THE CONGRUENCE OF AGENCY FIX POSITIONS. THE INITIAL INTENSITY REMAINS ASSESSED AT 55 KNOTS WITH MEDIUM CONFIDENCE BASED ON THE MEDIAN OF THE AGENCY CURRENT INTENSITY ESTIMATES, HEDGED SLIGHTLY HIGHER THAN THE ADT AND SATCON ESTIMATES. THE OVERALL STRUCTURE APPEARS SHEARED WITH AN AREA TO THE NORTH OF THE LLCC DEVOID OF ANY SIGNIFICANT CONVECTION. ANALYSIS OF A 160000Z UPPER-AIR SOUNDING FROM HEUKSANDO INDICATE THE PRESENCE OF VERY DRY AIR BETWEEN 300-600MB, WHICH SUPPORTS WHAT IS SEEN IN THE IMAGERY. ADDITIONALLY, WHILE HIGH-RESOLUTION HWRF SOUNDINGS AND CIMSS AUTOMATED UPPER-LEVEL ANALYSIS REVEALS LOW SOUTHERLY WIND SHEAR, THE SHARP NORTHERN EDGE OF THE CONVECTION FLARING NEAR THE CENTER CLEARLY SUPPORT A NORTHERLY SHEAR VECTOR OVER TOP OF THE SYSTEM, AND THE LATEST CIMSS ATMOSPHERIC MOTION VECTOR (AMV) ANALYSIS SUGGESTS THE PRESENCE OF A SMALL, WEAK ANTICYCLONE JUST NORTHWEST OF THE LLCC, WHICH WOULD SUPPORT A NORTHERLY WIND AT 200MB OVER TOP OF 19W. EXCEPTING THE DRY AIR AND THE NORTHERLY SHEAR, THE ENVIRONMENT OTHERWISE FAVORABLE WITH WARM SSTS AND ROBUST POLEWARD OUTFLOW.

TS 19W(CHANTHU). MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD AGREEMENT THROUGH LANDFALL, WITH ALL GUIDANCE MEMBERS CLOSELY CLUSTERED ABOUT THE MEAN WITH A LANDFALL ALONG THE NORTHWEST COAST OF KYUSHU AT 24H. THEREAFTER THE GUIDANCE DIVERGES, WITH HWRF AND GALWEM JUMPING CIRCULATION CENTERS AND TRACKING THE NORTHERN, SECONDARY LOW DISCUSSED ABOVE AS THE ALTERNATE SCENARIO. THE REMAINDER OF THE TRACKERS SHOW A TRACK GENERALLY EAST-NORTHEASTWARD THROUGH THE REMAINDER OF THE FORECAST PERIOD. HOWEVER, THE GFS, NAVGEM, EGRR AND ECMWF AND ITS ENSEMBLE MEAN HAVE AL SHOWN SIGNIFICANT CHANGES SINCE THE PREVIOUS RUN, AND NOW ALL AGREE ON A SLOWER TRACK SOUTH OF TOKYO THROUGH 72H. INTERESTINGLY, THE GFS AND UKMET ENSEMBLE MEAN TRACKERS REMAIN CONSISTENT WITH THE PREVIOUS RUNS AND INDICATE A FAST TRACK TO THE NORTHEAST, CONSISTENT WITH THE PREVIOUS FORECAST. WHILE THERE IS HIGH CONFIDENCE IN THE 0-24HR FORECAST TRACK, WITH SUCH A HIGH DEGREE OF UNCERTAINTY IN THE DETERMINISTIC GUIDANCE BEYOND 36H AND THE EXTREMELY LARGE SPREAD IN THE ENSEMBLE GUIDANCE, THERE IS OVERALL LOW CONFIDENCE IN THE JTWC FORECAST TRACK. INTENSITY GUIDANCE IS IN OVERALL GOOD AGREEMENT, THOUGH THE HWRF REMAINS UNREALISTICALLY HIGH AS IT JUMPS CIRCULATIONS. THE REMAINDER OF THE GUIDANCE REMAINS TIGHTLY CLUSTERED ABOUT THE CONSENSUS MEAN. THE JTWC FORECAST LIES SLIGHTLY HIGHER THAN THE MEAN WITH MEDIUM CONFIDENCE DUE TO THE UNCERTAINTIES ASSOCIATED WITH THE EXACT TRACK AND THUS THE AMOUNT OF TERRAIN INTERACTION.

16/00UTC.

ATLANTIC. INVEST 95L. TROPICAL CYCLONE FORMATION ALERT ISSUED AT 15/22UTC.

INVEST 95L. GUIDANCE.

INVEST 96L. TROPICAL CYCLONE FORMATION ALERT ISSUED AT 15/14UTC.

INVEST 96L. GUIDANCE.

16/06UTC