TY 20W(MINDULLE) CAT 3 through an eyewall replacement cycle//North Indian:TC 03B might re-emerge into the North Arabian Sea//Atlantic: 18L(SAM)CAT 4 update,27/03utc

JTWC IS ISSUING 6HOURLY WARNINGS ON 20W. 6HOURLY WARNINGS WERE DISCONTINUED ON 03B AT 26/21UTC. 3HOURLY SATELLITE BULLETINS ARE STILL ISSUED FOR BOTH SYSTEMS.

27/00UTC.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: THE SPUTTERING EYEWALL REPLACEMENT CYCLE COUPLED WITH UPWELLING CAUSED BY THE SLOW MOVEMENT OF TY 20W IS SUPPRESSING SYSTEM DEVELOPMENT, BUT EYE TEMPS HAVE WARMED OVER THE PAST SIX HOURS AND THE INNER EYEWALL IS MAINTAINING ORGANIZATION. IT WILL BE ANOTHER 24 HOURS BEFORE TY 20W LEAVES THE COOLER WATERS IN ITS WAKE AND HAS A BETTER SHOT AT RE-INTENSIFYING, BUT BY THEN THE SYSTEM WILL BE TRACKING INTO A REGION OF LOWER OCEAN HEAT CONTENT AND INCREASING VERTICAL WINDSHEAR (VWS). STILL, THE VERTICAL WIND SHEAR WILL NOT INCREASE SUBSTANTIALLY UNTIL THE STORM CROSSES THE 30TH LATITUDE. NEAR 96H THE SYSTEM WILL TRACK INTO A REGION OF MUCH GREATER VWS AND BEGIN INTERACTING WITH THE MID-LATITUDE WESTERLIES, BEGINNING THE EXTRA-TROPICAL TRANSITION PROCESS. AS TY 20W ROARS OFF-SHORE OF THE KANTO PLAIN, IT WILL BE TRANSITIONING INTO A MID-LATITUDE LOW AND INTERACTING WITH TRANSITORY AUTUMNAL HIGH PRESSURE SYSTEMS MOVING ACROSS NORTHERN JAPAN TO DRAW GALE TO STORM FORCE NORTHEASTERLIES OFF-SHORE OF HONSHU.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS TY 20 STILL STRUGGLING THROUGH AN EYEWALL REPLACEMENT CYCLE (ERC). THE MOAT BETWEEN THE ORIGINAL AND SECONDARY EYEWALL REMAINS OPEN AND THE NEW EYEWALL IS NOT FULLY FORMED OVER THE NORTHWESTERN QUADRANT AND ALMOST COMPLETELY LACKING IN DEEP CONVECTION. THE ORIGINAL EYEWALL, HOWEVER, IS HANGING IN THERE AND SEEMS RELUCTANT TO GIVE UP THE GHOST. EYEWALL CLOUD TOPS HAVE STOPPED WARMING AND ALTHOUGH THE 45KM RAGGED EYE HAS ACTUALLY SHOWED WARMER TEMPS OVER THE CORE DURING THE PAST SIX HOURS. DRY AIR ENTRAINMENT OVER THE WESTERN SEMICIRCLE IS EVIDENT IN BOTH SATELLITE IMAGERY AND TOTAL PRECIPITABLE WATER LOOPS. CURRENT HIGH RESOLUTION VISUAL IMAGERY CONFIRMS THE DRY SLOT, AS DOES THE MOST RECENT USEABLE MICROWAVE IMAGERY, A 262121Z SSMIS SERIES. THE MICROWAVE SHOWS A LACK OF DEEP CONVECTION OVER THE ENTIRE NORTHWEST SEMICIRCLE, BUT IT DOES CONFIRM THAT THE SYSTEM REMAINS TIGHTLY WRAPPED. THE WARMING CLOUD TOPS MAY BE ARTIFICIALLY LOWERING THE SATCON AND ADT ESTIMATES, WHILE THE SUBJECTIVE DVORAK ASSESSMENTS ARE BOUND BY CONSTRAINTS DUE TO THEIR RAPID DECLINE. THE INTENSITY ASSESSMENT AVERAGES THE SUBJECTIVE AGENCY ESTIMATES WITH THE AUTOMATED TECHNIQUES AND IS SUPPORTED BY THE CONTINUED TIGHT ORGANIZATION OF THE SYSTEM.

27/0039UTC.TY 20W HAS BEEN GOING THROUGH AN EYE-WALL RELACEMENT CYCLE WHICH STARTED NEAR 26/07UTC. THE MOAT SIGNATURE IS WELL DEPICTED ON THIS SATELLITE IMAGERY.

MODEL DISCUSSION: ON THE NEGATIVE SIDE, BOTH ECMWF AND GFS FAILED TO PREDICT THE DEVELOPMENT OF THE UPPER LEVEL ANTICYCLONE AND ITS ASSOCIATED HIGH AMPLITUDE RIDGE THAT FORMED OVER THE MARIANAS. PREVIOUSLY THEY SHOWED ONLY A BROAD AND LAZY WESTWARD EXTENSION OF THE BONIN HIGH. TY 20W HAS BEEN GETTING SQUEEZED BETWEEN THAT RIDGE AND ANOTHER UNDER-FORECASTED RIDGE EXTENDING FROM A 5940 500MB HEIGHT CENTER SOUTH OF SHANGHAI, WHICH HAS EXTENDED SO FAR OVER THE RYUKUS THAT IT HAS BEEN IMPEDING POLEWARD MOVEMENT OF THE SYSTEM. THAT SLOW MOVEMENT HAS INDUCED THE UPWELLING THAT IS RETARDING THE EYEWALL REPLACEMENT CYCLE AND CAUSING THE UPWELLING THAT IS WEAKENING THE STORM. SEA SURFACE TEMPERATURES ARE ALL THE WAY DOWN TO 25-27C NEAR THE CORE OF THE SYSTEM. ON THE POSITIVE SIDE, THAT EVENT HAS BEEN MASTERFULLY FORECASTED BY THE HWRF-P, AND THAT MODEL SHOWS THE VORTEX LEAVING THE EDDY AND MOVING BACK INTO WARMER WATERS NEAR 24H. OVERALL THOUGH, MODEL GUIDANCE HAS DONE AN OUTSTANDING JOB CAPTURING THE GENERAL TRACK OF THE STORM AND IS DOING NOTHING BUT GETTING TIGHTER WITH EACH SUCCESSIVE RUN. THERE IS INCREASING CONFIDENCE THAT THE CENTER OF THE STORM WILL STAY WELL SEAWARD OF THE KANTO PLAIN, ALTHOUGH ITS PROXIMITY WILL LIKELY INDUCE GALE TO STORM FORCE NORTHEASTERLIES OFF-SHORE. THE INTENSITY GUIDANCE IS SHOWING A MILD REINTENSIFICATION DURING THE TAU 24 TO 48 PERIOD AS THE STORM MOVES BACK INTO WARMER WATERS, BUT THERE IS ONLY SO MUCH TIME BEFORE THE STORM TRACKS NORTH OF THE 25TH LATITUDE AND INTO A REGION OF MUCH LOWER OCEAN HEAT CONTENT. THE GREATEST UNCERTAINTY WITH THE GUIDANCE IS THE EXTENT OF WINDFIELD EXPANSION DURING THE ETT PROCESS AS IT SHOOTS BY HONSHU, NEVER AN EASY TASK. THE JTWC TRACK FORECAST STAYS STRAIGHT ON THE MULTI-MODEL CONSENSUS, THE INTENSITY FORECAST RUNS A LITTLE ABOVE CONSENSUS, AND THE WINDFIELDS FOLLOW THE RVCN MODEL.

262100Z POSITION NEAR 18.4N 82.9E. 26SEP21. TROPICAL CYCLONE 03B (GULAB), LOCATED APPROXIMATELY 700KM SOUTHWEST OF KOLKATA, INDIA, HAS TRACKED WESTWARD AT 15 KM/H OVER THE PAST SIX HOURS. THE ENERGY ASSOCIATED WITH THE SYSTEM MAY CARRY OVER THE INDIAN SUBCONTINENT AND INTO THE NORTH ARABIAN SEA AT SOME POINT. THERE IS GREAT UNCERTAINTY WHERE PRECISELY THE VORTEX MIGHT RE-EMERGE INTO OPEN WATERS AND THE INTENSITY AT WHICH IT MIGHT DO SO, SO JTWC WILL CONTINUE TRACKING THE SYSTEM BUT FOREGO WARNINGS UNTIL SUCH TIME AS CONDITIONS WARRANT. THIS IS THE FINAL WARNING ON THIS SYSTEM BY THE JOINT TYPHOON WRNCEN PEARL HARBOR HI. THE SYSTEM WILL BE CLOSELY MONITORED FOR SIGNS OF REGENERATION.

TC 03B. TRACK AND INTENSITY GUIDANCE.

27/00UTC.

CURRENT INTENSITY IS 125KNOTS/CAT 4 AND IS FORECAST TO FALL AT 110KNOTS/CAT 3 BY 01/00UTC.

HU 18L(SAM). TRACK AND INTENSITY GUIDANCE.

27/04UTC.