WDPN31 PGTW 220300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (JELAWAT) WARNING NR 07// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 18W (JELAWAT), LOCATED APPROXIMATELY 540 NM EAST-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED SOUTH- SOUTHWESTWARD AT 03 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A TIGHTLY WRAPPED SYSTEM WITH DEEP CONVECTION WRAPPING INTO THE LOW LEVEL CIRCULATION CENTER (LLCC). A 212132Z SSMIS 91GHZ MICROWAVE IMAGE SHOWS SEVERAL DISPLACED DEEP CONVECTIVE BANDS OVER THE SOUTHERN SEMI-CIRCLE BUT VERY MINIMAL CONVECTIVE ACTIVITY OVER THE NORTHERN SEMICIRCLE. ANIMATED WATER VAPOR IMAGERY REVEALS A TUTT CELL HAS FORMED NORTHEAST OF THE SYSTEM WHICH IS WHAT IS SUPPRESSING THE CONVECTIVE ACTIVITY TO THE NORTH. FURTHER UPPER-LEVEL ANALYSIS DEPICTS THAT TS 18W LIES EQUATORWARD OF AN UPPER-LEVEL RIDGE AXIS WITH EXCELLENT EQUATORWARD OUTFLOW DUE TO SPEED DIVERGENCE TO THE SOUTH AND HAS LIMITED POLEWARD OUTFLOW DUE TO THE NEWLY FORMED TUTT CELL TO THE NORTHEAST. THE INITIAL POSITION IS BASED ON THE AFOREMENTIONED IMAGERY. THE INITIAL INTENSITY IS BASED ON AN AVERAGE OF DVORAK ESTIMATES OF 45 TO 55 KNOTS FROM RJTD AND PGTW, RESPECTIVELY. TS 18W IS IN A WEAK STEERING ENVIRONMENT AS AN APPROACHING MID- LATITUDE TROUGH HAS WEAKENED THE SUBTROPICAL RIDGE (STR) THAT WAS THE DOMINANT STEERING INFLUENCE. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 18W IS EXPECTED TO DRIFT SLOWLY WEST-SOUTHWESTWARD OVER THE NEXT 24 HOURS AS THE MID-LATITUDE TROUGH APPROACHING FROM THE NORTHWEST WEAKENS THE CURRENT STEERING RIDGE. AFTER THE TROUGH PASSES, THE SUBTROPICAL RIDGE WILL BEGIN TO REBUILD AND TURN TS 18W SLOWLY ON A MORE NORTH-NORTHWESTWARD TRACK. TS 18W WILL CONTINUALLY INTENSIFY AS IT DEVELOPS A POLEWARD OUTFLOW CHANNEL FROM THE PASSING TROUGH WITH THE POSSIBILITY OF RAPID INTENSIFICATION BASED ON THE FAVORABLE ENVIRONMENTAL CONDITIONS. C. IN THE EXTENDED TAUS, A SUBTROPICAL RIDGE THAT IS CURRENTLY OVER EASTERN CHINA IS FORECASTED TO AMPLIFY AND BECOME TS 18W'S DOMINANT STEERING MECHANISM, WHICH WILL TURN THE SYSTEM MORE TOWARDS THE WEST. DUE TO FORECASTED FAVORABLE ENVIRONMENTAL CONDITIONS, A PEAK INTENSITY OF 115 KNOTS IS FORECASTED AT TAU 96. NUMERICAL MODEL GUIDANCE REMAINS WIDELY SPREAD. THE CURRENT FORECAST REMAINS LEFT OF CONSENSUS TO OFFSET AN UNLIKELY SHARP NORTHERN TRACK INTO THE STR, WHICH IS DEPICTED BY GFS, EGRR AND JGSM. DUE TO THE LARGE SPREAD IN MODEL GUIDANCE, THERE IS LOW CONFIDENCE IN THE CURRENT TRACK FORECAST.// NNNN