WDPN31 PGTW 010300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (NYATOH) WARNING NR 007// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 13.8N 136.4E INITIAL INTENSITY: 60 KTS GEOGRAPHIC REFERENCE: 277 NM NORTH-NORTHWEST OF YAP MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS SIGNIFICANT WAVE HEIGHT: 22 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED VISUAL IMAGERY OVER THE PAST SIX HOURS SHOWS INTENSE BURSTS OF CONVECTION AND TIGHTENING AROUND THE CORE OF THE STORM. ALTHOUGH NO EYE IS PRESENT YET, AN ARC OF ESPECIALLY DEEP CONVECTIVE BANDING IS NOW EXTENDING FROM THE NORTHWEST QUADRANT ALL THE WAY AROUND TO THE SOUTHEASTERN QUADRANT. CONVECTIVE BURSTS ARE ALSO OBSERVABLE DIRECTLY OVER THE CORE. THE EFFECTS OF DRY AIR ENTRAINMENT MAY ALREADY BE WORKING ON THE SYSTEM, AS A DRY SLOT SURGING FROM THE NORTHERLIES WEST OF THE STORM IS BEGINNING TO WRAP ALL THE WAY AROUND THE CORE AND INTO THE NORTHWESTERN QUADRANT, CREATING SEPARATION BETWEEN THE CORE AND THE BANDING THAT WILL LIKELY BECOME THE EYEWALL. TROPICAL CYCLONE NYATOH IS TRACKING THROUGH A NEARLY IDEAL ENVIRONMENT FOR INTENSIFICATION, WITH EXCEPTIONALLY HIGH OCEAN HEAT CONTENT (OHC) AND LOW VERTICAL WINDSHEAR (VWS). ANIMATED WATER VAPOR IMAGERY SHOWS A BLOOM OF OUTFLOW IN ALL DIRECTIONS THAT BEGAN ABOUT TWELVE HOURS AGO AND CONTINUES TO EXPAND, APPEARING AS A ZONE OF ANTICYCLONIC EXHAUST THAT EXTENDS OVER 10 DEGREES OF LATITUDE. BOTH OBJECTIVE AND SUBJECTIVE DVORAKS ARE COMING INTO ALIGNMENT, AND THE CURRENT INTENSITY ASSESSMENT IS BARELY ON THE HIGH SIDE OF A CONSENSUS OF AGENCY DVORAKS, ADT, AND SATCON. THE SYSTEM IS ENTERING THE ZONE OF MAXIMUM INTENSIFICATION, BEGINNING A POLEWARD BEND AS IT ROUNDS THE SUBTROPICAL RIDGE. INITIAL WIND RADII BASIS: PERSISTENCE FROM A 301218Z ASCAT PASS. A NEW PASS CAME DURING THIS WRITING AND WIND RADII WILL BE ADJUSTED ON THE 010600Z WARNING. CURRENT STEERING MECHANISM: THE EXTREME SOUTHWESTERN FLANK OF THE SUBTROPICAL RIDGE. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS RJTD: T3.0 - 45 KTS KNES: T3.5 - 55 KTS CIMSS SATCON: 56 KTS AT 302202Z CIMSS ADT: 59 KTS AT 302340Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG RADIAL ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: HIGH INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: DURING THE NEXT 36 HOURS, TROPICAL STORM 27W WILL ROUND THE RIDGE AND REACH ITS MAXIMUM INTENSITY, TAKING ADVANTAGE OF A NEARLY IDEAL OUTFLOW SITUATION WHILE STILL REMAINING IN A REGION OF LOW VERTICAL WINDSHEAR AND HIGH OCEAN HEAT CONTENT. A COMBINATION OF THREE NEGATIVE FACTORS WILL BEGIN WEARING ON THE STORM AFTER IT PEAKS NEAR THE 18TH LATITUDE AT ABOUT TAU 36. VERTICAL WINDSHEAR ASSOCIATED WITH A DEEP MID-LATITUDE TROF WILL BE THE FIRST TO WEAR ON THE STORM, BEGINNING NEAR TAU 30 AND EXCEEDING 30KTS BY TAU 48. DRY AIR ENTRAINMENT WILL BEGIN WORKING ITS MISERY SHORTLY THEREAFTER AND BY TAU 60 THE CORE WILL BE COMPLETELY CONSTRICTED BY A WALL OF DRY, MODIFIED CONTINENTAL POLAR AIR. AND TO ADD THE COUP DE GRACE, THE SYSTEM WILL MOVE OUT OF FAVORABLE OCEAN HEAT CONTENT AND INTO DESTRUCTIVELY COOL WATERS BY THE TIME IT REACHES THE 20TH LATITUDE, NEAR TAU 48. FOR THE 36 HOURS AFTER THAT, TS 27W WILL WEAKEN AND ACCELERATE TOWARDS THE MID-LATITUDES, BUT BY THE TIME IT CROSSES THE TROPIC OF CANCER THE UPPER LEVELS WILL HAVE DECOUPLED FROM THE LOW LEVEL VORTEX, WHERE WHAT REMAINS OF THE LLCC WILL DRIFT UNTIL THE NEWLY EXTENDED SUBTROICAL RIDGE BUILDING OFF THE CONTINENT PICK IT UP AND DRIVES IT BACK TO THE WEST. MODEL DISCUSSION: INTENSITY GUIDANCE IS IN EXCELLENT AGREEMENT ON THE TIMING OF THE RAMP-UP, SHOWING A CLEAR PEAK AT AND JUST AFTER TAU 36. THERE IS, HOWEVER, A WIDE ENVELOPE OF POSSIBILITES, RANGING FROM 75 TO 115KTS. THE JTWC FORECAST LIES ON THE HIGH SIDE OF THE GUIDANCE PACKAGE BUT CONFIDENCE IN A PEAK INTENSITY OF AROUND 100KTS (NEAR THE 18TH LATITUDE) IS INCREASING. AS WOULD BE EXPECTED, THE ALONG-TRACK SPREAD BEGINS TO INCREASE DURING THE PERIOD WHEN THE SYSTEM ACCELERATES TOWARDS THE MID-LATITUDES (BETWEEN TAU 24 AND TAU 72), BUT THE CROSS TRACK SPREAD IS REASONABLY TIGHT. AFTER TAU 72, THE DECOUPLING PERIOD BEGINS, TRACK GUIDANCE IS SPREAD WILDLY AND CONFIDENCE IN THE TRACK DECREASES SHARPLY. OVER THE PAST 48 HOURS, GUIDANCE HAS BEEN CONSISTENT IN BOTH TRACK AND INTENSITY AND IS PLAYING OUT ACCURATELY, WITH THE ENSEMBLES BEING PARTICULARLY CONSISTENT IN PREDICTING A DECOUPLING SCENARIO. NONETHELESS, THERE IS ESPECIALLY LOW CONFIDENCE IN THE FORECAST AFTER TAU 72 DUE TO THE WIDE POSSIBILITES IN HOW THE DECOUPLING PROCESS PLAYS OUT AND WHERE THE LOW LEVEL VORTEX WINDS UP WHEN THE DECOUPLING IS COMPLETE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN