TC 13S(DJOUNGOU) Rapid Intensification possible// TC 14P// TC 15P/ 10 Day ECMWF Storm Tracks// 1603utc

JTWC IS ISSUING 6HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TC 14P AND TC 15P. JTWC IS ISSUING 12HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TC 13S.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: TROPICAL CYCLONE 13S (DJOUNGOU) APPEARS TO BE RAPIDLY FORMING A COMPACT INNER CORE STRUCTURE WITHIN AN ENVIRONMENT CONSISTING OF VERY WARM SEA SURFACE TEMPERATURES, LIGHT SHEAR, AND DEEP MOISTURE. THESE CONDITIONS ARE EXPECTED TO PERSIST FOR THE NEXT 36-48 HOURS AS DJOUNGOU TRACKS EASTWARD, GUIDED BY A MID-LATITUDE LONGWAVE TROUGH WELL TO THE SOUTHEAST. ADDITIONALLY, DJOUNGOU WILL PASS OVER AN EDDY OF LOCALLY HIGHER OCEAN HEAT CONTENT VALUES (IN EXCESS OF 60 KJ PER SQUARE CM) DURING THE 24-48 HOUR PERIOD. THIS ENVIRONMENT IS LIKELY TO FACILITATE RAPID INTENSIFICATION (RI) IN THE NEAR TERM, AND STATISTICAL RI AIDS SUPPORT THIS WITH 40-60 PERCENT PROBABILITIES OF RI DURING THE NEXT 48 HOURS. THE JTWC INTENSITY FORECAST BRINGS DJOUNGOU TO TYPHOON INTENSITY (65 KT) IN 24 HOURS AND TO 100 KT IN 48 HOURS. PEAK INTENSITY IS LIKELY TO OCCUR BETWEEN 48 AND 72 HOURS AS THE CYCLONE APPROACHES THE SUBTROPICAL JET, BENEFITING FROM CONSTRUCTIVE INTERFERENCE WITH A 130 KT JET STREAK TO THE SOUTHEAST THAT WILL PROVIDE SIGNIFICANT UPPER-LEVEL DIVERGENT FORCING OVER THE CYCLONE. BY 72 HOURS, VERTICAL SHEAR WILL INCREASE DRAMATICALLY AS DJOUNGOU NEARS THE JET AXIS, AND THE CYCLONE'S ACCELERATING SOUTHEASTWARD MOTION ALONG THE JET WILL BRING IT OVER COOLER WATERS, ULTIMATELY LOWER THAN 26 DEGREES CELSIUS BY 120 HOURS, LEADING TO RAPID WEAKENING. MOST DYNAMICAL MODELS PREDICT THAT DJOUNGOU WILL BEGIN EXTRATROPICAL TRANSITION AROUND 96 HOURS, ULTIMATELY BECOMING ABSORBED INTO A FRONTAL BOUNDARY BY 120 HOURS. THERE IS SIGNIFICANT ALONG-TRACK SPREAD DURING THE 72-120 HOUR PERIOD DUE TO UNCERTAINTY IN HOW QUICKLY THE CYCLONE WILL VERTICALLY DECOUPLE AND WHETHER THE MID-LATITUDE TROUGH WILL FULLY ENTRAIN IT.

MODEL DISCUSSION: DYNAMICAL MODEL GUIDANCE HAS FAIRLY TIGHT CROSS-TRACK SPREAD THROUGH THE FORECAST PERIOD, BUT ALONG-TRACK SPREAD GROWS DRAMATICALLY DURING THE 72-120 HOUR PERIOD. THE JTWC FORECAST IS CLOSE TO THE MULTI-MODEL CONSENSUS, BUT LEANS TOWARDS THE SLOWER ECMWF, ECMWF ENSEMBLE MEAN, AND GFS ENSEMBLE MEAN BEYOND 72 HOURS DUE TO BETTER RUN-TO-RUN CONSISTENCY. THE JTWC INTENSITY FORECAST IS A BIT ABOVE THE MULTI-MODEL CONSENSUS, TAKING INTO ACCOUNT THE EXPECTATION FOR RAPID INTENSIFICATION DURING THE FIRST 48 HOURS.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT BUT PARTIALLY EXPOSED LOW-LEVEL CIRCULATION WITH CORE CONVECTION CONFINED TO THE WESTERN SIDE. NORTHERLY OR NORTHEASTERLY SHEAR IS EVIDENT IN SATELLITE IMAGERY WITH UPPER-LEVEL CIRRUS CLOUDS STREAMING INTO THE LLC LOCATION FROM THE NORTHEAST. THE STORM HAS BEEN QUASISTATIONARY OVER THE PAST SIX HOURS. THE INITIAL INTENSITY IS HELD AT 35 KT BASED ON AGENCY DVORAK ESTIMATES OF T2.5 (35 KT) AND LITTLE CHANGE IN OBSERVED SURFACE WINDS AT CENTRE ISLAND NEAR THE DEEP CONVECTION ON THE WESTERN SIDE OF THE LLC, RANGING FROM 30 TO 33 KT (10-MINUTE AVERAGED) IN RECENT HOURS.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TROPICAL CYCLONE 14P HAS BEEN QUASISTATIONARY FOR THE PAST SIX HOURS, MIRED IN WEAK STEERING CURRENTS BETWEEN TWO MID-LEVEL RIDGES OVER WESTERN AUSTRALIA AND THE CORAL SEA. HOWEVER, MODELS REMAIN IN AGREEMENT THAT A NET NORTHEASTERLY STEERING FLOW WILL DEVELOP SHORTLY AND PUSH 14P SOUTHWESTWARD AND INLAND OVER NORTHERN AUSTRALIA WITHIN THE NEXT 12 HOURS. DISSIPATION AND A SUBSEQUENT TRACK OF THE REMNANTS WESTWARD ACROSS NORTHERN AUSTRALIA WILL ENSUE. THIS TRACK COULD POTENTIALLY CARRY THE REMNANTS OUT INTO THE SOUTHEAST INDIAN OCEAN IN SEVERAL DAYS, AT WHICH POINT MODELS SUGGEST REGENERATION IS POSSIBLE. SHOULD THE REMNANTS IN FACT SURVIVE AND REEMERGE OVER WATER, THEY WILL BE MONITORED FOR REGENERATION.

MODEL DISCUSSION: DYNAMICAL MODEL GUIDANCE IS IN GOOD AGREEMENT ON THE STORM TRACK DURING THE FORECAST PERIOD, AND THE JTWC FORECAST IS CLOSE TO THE MULTI-MODEL CONSENSUS. THE JTWC INTENSITY FORECAST IS CLOSE TO THE MEAN OF THE OVERLAND DECAY FORECAST FROM AVAILABLE GLOBAL MODELS.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A WELL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC) THAT IS APPROACHING A MID-LATITUDE FRONTAL ZONE ON THE NORTHEASTERN FLANK OF AN UPPER-LEVEL TROUGH. A 1929Z GMI MICROWAVE PASS AND A 2356Z ATMS MICROWAVE PASS SHOW THAT TIGHT CONVECTIVE BANDING EXISTS NEAR THE LLCC BUT IS ONLY WRAPPING AROUND THE NORTHERN AND EASTERN SIDES, LIKELY DUE TO MODERATE SOUTHWESTERLY SHEAR. THE INITIAL INTENSITY IS SET AT 40 KTS BASED ON A BLEND OF AGENCY DVORAK ESTIMATES AND OBJECTIVE SATELLITE INTENSITY ESTIMATES FROM CIMSS. STRONG POLEWARD OUTFLOW IS EVIDENT IN SATELLITE IMAGERY TOWARDS THE JET STREAK TO THE SOUTHEAST OF THE CYCLONE. AITUTAKI ISLAND ABOUT 210 NM TO THE EAST-SOUTHEAST HAS BEEN OBSERVING SUSTAINED NORTHEASTERLY WINDS OF 21-22 KT DURING THE PAST FEW HOURS.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TROPICAL CYCLONE 15P IS ACCELERATING SOUTHEASTWARD AS IT APPROACHES A FRONTAL BOUNDARY AND UPPER-LEVEL TROUGH TO THE SOUTH. THIS WILL INITIATE THE PROCESS OF EXTRATROPICAL TRANSITION IN ABOUT 12 HOURS AS VERTICAL SHEAR AND BAROCLINICITY DRAMATICALLY INCREASE. GLOBAL MODELS ARE IN GOOD AGREEMENT THAT 15P WILL BECOME A FRONTAL CYCLONE IN ABOUT 36 HOURS. THE INTENSITY FORECAST SHOWS POTENTIAL FOR A SLIGHT INCREASE IN MAXIMUM WINDS TO AROUND 45 KT DUE TO BAROCLINIC ENHANCEMENT OF THE WIND FIELD, WHICH DYNAMICAL MODELS ALSO AGREE ON.

MODEL DISCUSSION: DYNAMICAL MODELS ARE IN TIGHT AGREEMENT ON THE TRACK AND INTENSITSY FORECASTS, AND THE JTWC FORECAST IS CLOSE TO THE MULTI-MODEL CONSENSUS.