Typhoon 20W(KRATHON) up 45 Knots past 24 hours forecast to intensify within 24/48h approaching Southern TAIWAN// TS 19W(JEBI)//2909utc

JTWC IS ISSUING 6HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON 19W AND ON 20W.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON 20W (KRATHON) OPENED UP A BROAD, RAGGEDLY-DEFINED EYE SEVERAL HOURS AGO WHICH HAS SINCE BECOME CLOUD-FILLED. THE OUTFLOW COULD BE DESCRIBED AS MODERATE RADIAL BUT IS MOST PRONOUNCED IN THE EQUATORWARD DIRECTION DUE TO ITS BROAD EXTENT REACHING THE VIGOROUS NORTHEASTERLY FLOW OVER THE PHILIPPINES. THE SYSTEM IS HINTING AT OPENING UP A POLEWARD OUTFLOW CHANNEL INTO THE MID-LATITUDE WESTERLIES, BUT IT HAS NOT YET CONNECTED WITH THIS MECHANISM. DEEP CONVECTION IS EVIDENT, PARTICULARLY ON THE NORTHEAST SIDE WITHIN AN INNER AND OUTER BAND, BUT THE OVERALL SYMMETRY SUGGESTS THE SYSTEM IS QUICKLY BECOMING BETTER ORGANIZED. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON PLACEMENT WITHIN THE VERY BROAD, RAGGED EYE EVIDENT ON ANIMATED MSI IMAGERY. THE INITIAL INTENSITY OF 80 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A BLEND OF THE CURRENT INTENSITY AND DVORAK ESTIMATES LISTED.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: THE SYSTEM IS EXPECTED TO CONTINUE STRENGTHENING AT RAPID INTENSIFICATION (RI) LEVELS THROUGHOUT THE DURATION OF ITS EXPECTED TRACK SLOWLY NORTHWESTWARD, PASSING THROUGH THE LUZON STRAIT OVER EXCESSIVELY WARM SSTS AND FAVORABLE VERTICAL WIND SHEAR VALUES OF 5-10 KTS. THE HIGH OCEAN HEAT CONTENT VALUES ACROSS THE LUZON STRAIT ALLEVIATE CONCERN OF A DEPLETION OF WARM WATER FUELING THE INTENSIFICATION. THE PERIOD OF STRENGTHENING WILL LEVEL OFF BY TAU 48 DUE TO INCREASING LAND INTERACTION TAIWAN. THE EXPECTED TRACK WILL CURVE SHARPLY TO THE NORTHEAST AND TAKE THE CORE OF THE SYSTEM ACROSS THE SOUTHERN (HENGCHUN) PENINSULA OF TAIWAN. A QUICK DECAY IN KRATHON'S STRENGTH WILL OCCUR NEAR TAU 72 AND AFTER. THE WIND FIELD, WHICH IS ALREADY EXTENSIVE FOR THIS SYSTEM, WILL GRADUALLY EXPAND WITH THE ONSET OF INTENSITY DECLINE. TYPHOON KRATHON WILL BEGIN TO ACCELERATE NORTHEASTWARD THROUGH THE EAST CHINA SEA AS THE SUBTROPICAL RIDGE TO THE EAST LATCHES ON AS THE DOMINANT STEERING INFLUENCE DRIVER.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS LARGELY PREDICTING A NEARLY RIGHT-ANGLE TURN SOUTH OF TAIWAN WITH SOME OF THE LESS RELIABLE MODELS PULLING THE CONSENSUS TOO FAR WEST AT THIS PIVOT POINT. THERE IS GOOD AGREEMENT WITH A NORTHEASTWARD TRACK FOLLOWING A POSSIBLE LANDFALL IN SOUTHERN TAIWAN NEAR TAU 60. THE UNCERTAINTY REGARDING LANDFALL INTRODUCES A GREATER CHANCE FOR TRACK ERRORS AFTER TAU 72 AND IS REFLECTED IN THE POOR AGREEMENT IN INDIVIDUAL TRACKERS RUN-TO-RUN AND THEIR OVERALL CONSENSUS. INTENSITY GUIDANCE IS SUPPORTIVE OF THE IMMEDIATE RAPID INTENSIFICATION PERIOD. DEVELOPMENT BEGINS TO LEVEL OFF BY TAU 48, WHEN THE NUMERICAL MODELS BEGIN TO ACCOUNT FOR THE LAND INTERACTION NEAR TAIWAN. INTENSITY GUIDANCE IS IN GOOD AGREEMENT WITH THE TIMING AND RATE OF DECLINE THROUGH TAU 120. UNCERTAINTIES IN THE FORECAST ARE DUE TO THE INITIAL INTENSITY UNCERTAINTIES STEMMING FROM LACK OF DATA AND ALSO DUE TO THE UNKNOWN EXTENT OF LAND INTERACTION WITH TAIWAN.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED WATER VAPOR IMAGERY AND UW-CIMSS UPPER-LEVEL WINDS REVEAL A SLOWLY IMPROVING ENVIRONMENT, WITH THE BROAD UPPER-LEVEL LOW AND LARGE SUBSIDENT REGION SHIFTING TO A SLIGHTLY MORE FAVORABLE CONFIGURATION TO THE WEST, ALLOWING FOR IMPROVED POLEWARD VENTING. AS INDICATED IN ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI), DEEP CONVECTION HAS BEGUN TO BUILD OVER THE BROAD CENTER. HOWEVER, DUE TO THE BROAD NATURE OF THE CENTER, THERE ARE MULTIPLE MESOVORTICIES ROTATING CYCLONICALLY AROUND A DEFINED CENTROID. THUS, THERE IS MEDIUM CONFIDENCE IN THE INITIAL POSITION. THE INITIAL INTENSITY IS ASSESSED AT 35 KNOTS BASED ON RECENT SCATTEROMETRY DATA, WHICH IS ALSO SUPPORTED BY CIMSS OBJECTIVE INTENSITY ESTIMATES.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TROPICAL STORM (TS) 19W IS FORECAST TO TRACK NORTHWARD ALONG THE WESTERN PERIPHERY OF THE STR THROUGH TAU 36. STEADY INTENSIFICATION IS ANTICIPATED AS THE UPPER-LOW TO THE WEST, CURRENTLY INHIBITING SIGNIFICANT INTENSIFICATION, FILLS ALLOWING FOR IMPROVED POLEWARD VENTING. AFTER TAU 36, THE SYSTEM WILL BEGIN TO ROUND THE STR AND COMMENCE EXTRA-TROPICAL TRANSITION (ETT) AS IT INTERACTS WITH A SHORTWAVE TROUGH SOUTH OF MAINLAND JAPAN. THE PEAK INTENSITY OF 60 KNOTS WILL OCCUR NEAR TAU 48 DUE TO ROBUST POLEWARD OUTFLOW INTO THE AFOREMENTIONED UPPER-LEVEL TROUGH. THE SYSTEM WILL COMPLETE ETT BY TAU 72 AS IT ACCELERATES INTO THE MIDLATITUDE WESTERLIES EAST OF HOKKAIDO AND RAPIDLY GAINS FRONTAL CHARACTERISTICS. AFTER TAU 60, THE SYSTEM WILL WEAKEN QUICKLY DUE TO INCREASING VERTICAL WIND SHEAR AND COOLER SST VALUES LESS THAN 25C.

MODEL DISCUSSION: DETERMINISTIC AND PROBABILISTIC TRACK GUIDANCE REMAINS IN FAIR AGREEMENT THROUGH THE FORECAST PERIOD, WITH GUIDANCE INDICATING SOME POTENTIAL FOR THE SYSTEM TO TRACK CLOSER TO THE KANTO PLAIN REGION. THE BULK OF THE SOLUTIONS, HOWEVER, REMAIN WELL EAST OF HONSHU. NUMERICAL GUIDANCE CONTINUES TO INDICATE A RELATIVELY SMALL GALE-FORCE WIND AREA ASSOCIATED WITH THE SYSTEM, WHICH WILL LIMIT THE IMPACT ON CENTRAL HONSHU AS THE SYSTEM PASSES.