WDPN31 PGTW 041500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 06W (NOUL) WARNING NR 07// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 06W (NOUL), LOCATED APPROXIMATELY 95 NM EAST OF YAP, HAS TRACKED WEST-SOUTHWESTWARD AT 03 KNOTS OVER THE PAST SIX HOURS. THE CURRENT POSITION IS BASED ON RECENT MICROWAVE SATELLITE DATA INCLUDING A 040923Z SSMIS PASS AND A 041141Z METOP-B IMAGE. THE INTENSITY OF 45 KNOTS IS CONSISTENT WITH DVORAK SATELLITE ESTIMATES FROM MULTIPLE REPORTING AGENCIES AS WELL AS SCATTEROMETER DATA FROM A 041141Z ASCAT PASS. TS 06W HAS TRACKED SLOWLY WEST- SOUTHWESTWARD UNDER THE STEERING INFLUENCE OF WEAK SUBTROPICAL RIDGING TO THE NORTH OVER THE PAST SIX HOURS. DEEP CONVECTION HAS INCREASED OVER A TIGHTLY-WRAPPED BAND SITUATED ALONG THE WESTERN PERIPHERY OF THE LOW LEVEL CIRCULATION CENTER. MODERATE EASTERLY VERTICAL WIND SHEAR AND A FAVORABLE OUTFLOW PATTER CONTINUES TO INFLUENCE THE SYSTEM, WHICH IS SITUATED EQUATORWARD OF AN UPPER- LEVEL RIDGE AXIS. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS WARNING. B. TS 06W IS EXPECTED TO TRACK SLOWLY WESTWARD OVER THE NEXT 36 HOURS UNDER THE CONTINUED STEERING INFLUENCE OF SUBTROPICAL RIDGING TO THE NORTH. AFTER TAU 36, THE SUBTROPICAL RIDGE IS EXPECTED TO BUILD AND REORIENT AS A MID-LATITUDE TROUGH THAT HAS WEAKENED RIDGE MOVES EASTWARD. THIS REORIENTED RIDGE WILL ACCELERATE THE SYSTEM ALONG A WEST-NORTHWESTWARD TRAJECTORY. THE CYCLONE SHOULD STEADILY INTENSIFY OVER THE NEXT 72 HOURS DUE TO PASSAGE OVER VERY WARM WATER AND MODERATELY FAVORABLE UPPER-LEVEL CONDITIONS. NUMERIC MODEL GUIDANCE IS IN FAIR AGREEMENT THROUGH TAU 72. THERE IS SOME DIVERGENCE AMONG SOLUTIONS, BUT ALL MODELS WITH THE EXCEPTION OF GFDN INDICATE A WESTWARD TO WEST-NORTHWESTWARD TRACK OVER OR SLIGHTLY TO THE NORTH OF YAP. THE CURRENT JTWC FORECAST LIES CLOSE TO THE MULTI-MODEL CONSENSUS, NEAR THE CENTER OF THE PRIMARY MODEL GROUPING. C. IN THE EXTENDED PERIOD, TS 06W IS EXPECTED TO MOVE WEST- NORTHWESTWARD INTO THE PHILIPPINE SEA. THE SYSTEM SHOULD MAINTAIN INTENSITY OR PERHAPS INTENSIFY FURTHER AS ENVIRONMENTAL CONDITIONS REMAIN GENERALLY FAVORABLE. MODEL TRACK FORECAST SOLUTIONS DIVERGE MORE NOTICEABLY AFTER TAU 72, WITH A GROUPING CONSISTING OF GFS, GEFS, HWRF, AND COAMPS-TC DEPICTING A MORE POLEWARD TRACK AND A SECOND GROUPING CONSISTING OF ECMWF, NAVGEM, THE UKMET MODEL, AND THE JAPANESE TC-EPS DEPICTING A FLATTER TRACK TO THE WEST-NORTHWEST. THE CURRENT FORECAST FAVORS THE LATTER GROUPING BASED ON ANTICIPATED EVOLUTION OF THE SUBTROPICAL STEERING RIDGE. HOWEVER, GIVEN CURRENT MODEL SPREAD, THERE IS LOW CONFIDENCE IN THE JTWC TRACK FORECAST.// NNNN