WDPN31 PGTW 032100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MUN) WARNING NR 009// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 29.0N 145.0E INITIAL INTENSITY: 60 KTS GEOGRAPHIC REFERENCE: 464 NM SOUTHEAST OF YOKOSUKA, JAPAN MOVEMENT PAST 6 HOURS: NORTHWARD AT 06 KTS SIGNIFICANT WAVE HEIGHT: 24 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL STORM (TS) 04W (MUN) PRESENTS AS A VERY COMPACT SYSTEM, BECOMING INCREASINGLY ISOLATED FROM ITS ENVIRONMENT IN ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY. DEEP CONVECTIVE ACTIVITY HAS BLOOMED OVERNIGHT, ORGANIZED INTO A SMALL CDO FEATURE AND REACHED ITS PEAK IN TERMS OF COLDEST CLOUD TOP TEMPERATURES AT AROUND 031700Z, FOLLOWED BY RAPID WARMING IN THE SUBSEQUENT HOURS. A 031628Z AMSR2 COLOR-ENHANCED 89GHZ IMAGE DEPICTS WELL-ORGANIZED LOW-LEVEL BANDING FEATURES WRAPPING INTO SHARPLY OUTLINED LOW LEVEL CIRCULATION CENTER (LLCC). CONVECTIVELY HOWEVER, THE SYSTEM IS HIGHLY ASYMMETRIC, WITH SIGNIFICANT CONVECTIVE ACTIVITY ISOLATED TO THE NORTH AND EASTERN PORTIONS OF THE CIRCULATION, PRIMARILY DUE TO THE INFLUENCE OF PERSISTENT MID-LEVEL DRY AIR ACROSS THE SOUTHWESTERN PORTION OF THE CIRCULATION. A 031901Z SSMIS 91GHZ IMAGE CONFIRMS THE STRUCTURAL ASYMMETRIES, AND AN ARCHER ANALYSIS OF SAID MICROWAVE IMAGE SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, ASSESSED SIGNIFICANTLY HIGHER THAN ALL OF THE OBJECTIVE INTENSITY ESTIMATES, WHICH ARE LIKELY UNDER-ESTIMATING THE INTENSITY (BASED ON EARLIER SAR AND ASCAT DATA) DUE TO THE SMALL SIZE OF THE SYSTEM AND SLIGHTLY HIGHER THAN THE MOST AGGRESSIVE SUBJECTIVE DVORAK CI ESTIMATES. THE ENVIRONMENT IS MARGINALLY FAVORABLE, CHARACTERIZED BY WARM SSTS, AND LOW SHEAR. HOWEVER, THE PRESENCE OF AN UPPER-LEVEL CYCLONIC ROTATION OVER TOP OF THE SYSTEM, AS REVEALED IN ANIMATED WATER VAPOR IMAGERY AS WELL AS CIMSS AMV AND CIRA DMW PRODUCTS IS SQUASHING UPPER-LEVEL OUTFLOW FOR THE TIME BEING. FURTHERMORE, THE SYSTEM CONTINUES TO STRUGGLE WITH THE LINGERING EFFECTS OF DRY MID-LEVEL AIR PERSISTING ACROSS HALF OF THE CIRCULATION. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) COMPLEX EXTENDING FROM THE CENTRAL PHILIPPINES, EASTWARD TO THE CENTRAL MARIANAS, AND THEN NORTHEASTWARD TO NEAR 30N 160E. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS RJTD: T2.5 - 35 KTS KNES: T3.5 - 55 KTS CIMSS SATCON: 47 KTS AT 031600Z CIMSS ADT: 39 KTS AT 031800Z CIMSS AIDT: 41 KTS AT 031800Z CIMSS D-MINT: 37 KTS AT 031630Z CIMSS D-PRINT: 39 KTS AT 031830Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 26-27 CELSIUS OUTFLOW: WEAK POLEWARD OTHER FACTORS: CYCLONIC CIRCULATION OVER TOP OF THE CIRCULATION AS WELL AS DRY MID-LEVEL AIR OVER THE SOUTHWESTERN PORTION OF THE SYSTEM. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: OVER THE PAST SIX HOURS, TS 04W HAS SLOWED DOWN A GOOD BIT, WHILE WOBBLING SLOWLY AS IT MOVES INTO A SLIGHTLY WEAKER STEERING FLOW. THE RIDGE COMPLEX TO THE EAST IS STARTING TO BREAK OFF INTO DISTINCT CENTERS OF ANTICYCLONIC FLOW, WITH THE MAIN AREA OF INTEREST FOCUSED OVER THE NORTHERN MARIANAS. AS THIS SUBTROPICAL RIDGE (STR) CENTER BUILDS, THE ENTIRE RIDGING PATTERN FLATTENS OUT AS THE NORTHERN EXTENSION ERODES FROM THE NORTH. THIS WILL ALLOW TS 04W TO SLOWLY SHIFT ONTO A MORE EAST-NORTHEASTWARD TRACK FROM ABOUT TAU 12 THROUGH TAU 48. SIGNIFICANT WARM AIR ADVECTION ACROSS A DEEP LAYER OF THE ATMOSPHERE DUE TO A DEEP SOUTHWESTERLY SURGE FLOW WILL BUILD A BUBBLE-RIDGE TO THE EAST OF TS 04W BY TAU 60, FORCING THE SYSTEM ONTO A MORE NORTHWARD TRACK FROM THIS POINT THROUGH THE END OF THE FORECAST PERIOD. IF THE RIDGE GETS STRONG ENOUGH, AS INDICATED IN SOME MODELS (GFS), IT COULD BUILD WESTWARD AND RESULT IN A BIT MORE OF A NORTHWESTWARD TRACK BETWEEN TAU 72 AND TAU 96. REGARDLESS, BY THE END OF THE FORECAST, THE TRACK WILL SHIFT MORE TOWARDS THE NORTH-NORTHEAST ONCE MORE AS THE REMNANT SYSTEM BEGINS TO BE PULLED INTO A BREAK IN THE RIDGE AND INTO A MID-LATITUDE TROF PASSING TO THE NORTH. IN TERMS OF INTENSITY, THE ISOLATION OF THE SYSTEM FROM ANY SIGNIFICANT SOURCE OF OUTFLOW ALOFT, AND THE CONTINUED INFLUENCE OF DRY AIR, WILL HINDER INTENSIFICATION IN THE NEAR TERM. UPPER-LEVEL OUTFLOW IS SET TO IMPROVE AFTER TAU 18 WITH THE APPROACH OF A WEAK UPPER-LEVEL TROF PROVIDING A BOOST OF DIVERGENT POLEWARD OUTFLOW. AT THE SAME TIME, THE BULK OF MODEL DATA SUPPORTS A MOISTENING OF THE CIRCULATION, AND THE COMBINED EFFECTS WILL ALLOW FOR A SHORT PERIOD OF INTENSIFICATION THROUGH TAU 48. THE SYSTEM IS EXPECTED TO CROSS THE 26C AROUND TAU 60, AND WILL BEGIN THE WEAKENING STAGE AT THIS POINT. A STRONG UPPER-LEVEL TROF WILL SLAM INTO THE SYSTEM AROUND TAU 72, USHERING IN A SEVERE INCREASE IN SHEAR AND DRY AIR, EFFECTIVELY DECAPITATING THE SYSTEM AND MARKING THE BEGINNING OF SUBTROPICAL TRANSITION (STT). THE SYSTEM WILL CONTINUE TRACKING POLEWARD WHILE STEADILY WEAKENING AND COMPLETING STT BY THE END OF THE FORECAST PERIOD. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT ON THE OVERALL TRACK SCENARIO, WITH LITTLE IN THE WAY OF CROSS- OR ALONG-TRACK SPREAD IN THE SHORT-TERM FORECAST PERIOD (48 HOURS). GFS AND GEFS CONTINUE TO BE THE RIGHTMOST OUTLIERS, TAKING THE SYSTEM ON A FLATTER TRAJECTORY TO THE EAST THAN THE OTHER MEMBERS OF THE CONSENSUS, WHICH ARE A CONFINED TO A TIGHTLY PACKED ENVELOPE THROUGH TAU 48. THE JTWC FORECAST IS POSITIONED NEAR THE CONSENSUS MEAN WITH HIGH CONFIDENCE IN THE INITIAL 48 HOURS OF THE FORECAST. IN THE LONGER-RANGE FORECAST, GUIDANCE BEGINS TO DIVERGE SIGNIFICANTLY. THE NAVGEM, IN LINE WITH ITS KNOWN BIASES, RACES THE SYSTEM OFF TO THE NORTHEAST SUCH THAT BY TAU 120, IT IS POSITIONED SOUTHWEST OF ADAK, THE GALWEM FINDS ITSELF NEAR THE KURIL ISLANDS AND THE GFS IS SITUATED SOUTHEAST OF HONSHU. THE REMAINDER OF THE GUIDANCE, IN PARTICULAR THE ECWMF, EC-AIFS, AND GEFS, ARE GROUPED ROUGHLY IN THE MIDDLE BETWEEN THESE OUTLIERS, AND TRACKING AT A MUCH SLOWER SPEED. OVERALL TRACK SPREAD INCREASES TO 1260NM BY TAU 120. THE JTWC FORECAST IS PLACED ROUGHLY BETWEEN THE ECMWF AND AIFS TRACKERS WITH LOW CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT ON THE INTENSITY TREND WITH A 15-20 KNOT SPREAD IN POSSIBLE PEAK INTENSITIES BETWEEN 60-80 KNOTS. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN