WDPS31 PGTW 031500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (EIGHTEEN) WARNING NR 003// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 26.3S 174.3E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 388 NM EAST-NORTHEAST OF KINGSTON IS. MOVEMENT PAST 6 HOURS: WESTWARD AT 06 KTS SIGNIFICANT WAVE HEIGHT: 21 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN EXPANSIVE SYSTEM WITH MOST OF THE CENTRAL CONVECTION TOWARDS THE POLEWARD AND EASTERN SIDE WITH STRONG EASTWARD OUTFLOW. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A PARTIALLY EXPOSED LLC. THE INITIAL INTENSITY IS SET WITH MEDIUM CONFIDENCE WITH MULTIPLE AGENCY DVORAK ESTIMATES RANGING FROM T2.5(35KTS) TO T3.0(45KTS) AS LISTED BELOW. ANALYSIS INDICATES A MARGINALLY UNFAVORABLE ENVIRONMENT WITH STRONG VWS OFFSETTING THE STRONG EASTWARD OUTFLOW AND WARM SST. INITIAL WIND RADII BASIS: PERSISTENCE. CURRENT STEERING MECHANISM: NEAR EQUATORIAL RIDGE (NER) TO THE NORTH AND SUBTROPICAL RIDGE (STR) TO THE SOUTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS KNES: T2.5 - 35 KTS NZKL: T3.0 - 45 KTS CIMSS ADT: 39 KTS AT 031210Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY UNFAVORABLE VWS: 25-30 KTS SST: 26-27 CELSIUS OUTFLOW: STRONG EASTWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 18S IS MOVING SLOWLY AGAINST THE UPPER-LEVEL FLOW DUE TO THE NER RECEDING AND THE STR BUILDING IN FROM THE SOUTH AND EAST. ONCE THE STR ASSUMES ALL STEERING FROM THE NER, TC 18P WILL CONTINUALLY MOVE TO THE WEST-SOUTHWESTWARD AGAINST THE GENERAL UPPER-LEVEL FLOW, DECOUPLING THE MAIN BODY OF CONVECTION FROM THE LLC. THE PEAK INTENSITY FOR TC 18P IS HOLDING AT 40 KNOTS BUT WILL DECREASE MORE RAPIDLY IN THE SHORT TERM AS THE VWS INCREASES IN THE MARGINALLY UNFAVORABLE ENVIRONMENT. TC 18P IS EXPECTED TO WEAKEN IN INTENSITY DUE TO THE INCREASE OF VWS, REDUCING THE SYSTEM BELOW THE JTWC WARNING CRITERIA JUST AFTER TAU 36 AND IS EXPECTED TO DISSIPATE OVER WATER BY TAU 48, IF NOT SOONER. MODEL DISCUSSION: NUMERICAL MODELS ARE INCREASING IN DISPARITY AS THE SYSTEM MOVES BACK TOWARDS THE WEST. GIVEN THE UNCERTAINTY, THERE IS LOW CONFIDENCE IN THE INITIAL JTWC TRACK FORECAST ON THIS SYSTEM WHICH IS LAID SLIGHTLY TO THE RIGHT OF MODEL CONSENSUS. FORECAST CONFIDENCE: TRACK 0 - 72 HR: LOW INTENSITY 0 - 72 HR: LOW// NNNN