WDPN31 PGTW 020300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W (NALGAE) WARNING NR 025// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 20.5N 115.2E INITIAL INTENSITY: 50 KTS GEOGRAPHIC REFERENCE: 122 NM SOUTH-SOUTHEAST OF HONG KONG MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 06 KTS SIGNIFICANT WAVE HEIGHT: 28 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAPIDLY DETERIORATING SYSTEM WITH LOW-LEVEL CLOUD BANDS WRAPPING INTO AN EXPOSED, WELL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE MSI. A 012229Z SSMIS 91GHZ COLOR COMPOSITE MICROWAVE IMAGE REVEALS TIGHTLY WRAPPED SHALLOW BANDING WRAPPING INTO THE LLCC WITH DISORGANIZED, ISOLATED DEEP CONVECTION SHEARED TO THE NORTH. TS 26W IS LOCATED UNDER UPPER-LEVEL SOUTHWESTERLY FLOW WITH LOW TO MODERATE VERTICAL WIND SHEAR (VWS). SST VALUES ACROSS THE REGION ARE MARGINAL AT 25- 26C. ADDITIONALLY, THERE IS SIGNIFICANT DRY AIR PRESENT OVER SOUTHEAST CHINA, WHICH IS NOW ENTRAINING INTO THE SOUTHERN PERIPHERY OF THE SYSTEM. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE PGTW, RJTD DVORAK ESTIMATES AND THE CIMSS ADT ESTIMATE. ADDITIONALLY, A 020000Z SHIP OBSERVATION, APPROXIMATELY 137NM NNE OF THE CENTER, INDICATES 52 KNOT WINDS. INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST AND NORTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T3.0 - 45 KTS KNES: T4.0 - 65 KTS CIMSS ADT: 51 KTS AT 012340Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 10-15 KTS SST: 25-26 CELSIUS OUTFLOW: MODERATE POLEWARD AND EQUATORWARD OTHER FACTORS: DRY AIR ENTRAINMENT 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: TS 26W IS TRACKING SLOWLY NORTH-NORTHWESTWARD DUE TO THE COMBINED STEERING INFLUENCE OF A STR POSITIONED TO THE EAST AND ANOTHER BROADER STR POSITIONED TO THE NORTH. THE SYSTEM IS EXPECTED TO TURN WESTWARD THEN WEST-SOUTHWESTWARD AFTER TAU 24 AS THE STR POSITIONED OVER CHINA BECOMES THE DOMINANT STEERING INFLUENCE. DUE TO THE MARGINAL CONDITIONS, PARTICULARLY DRY AIR ENTRAINMENT AND FRICTIONAL EFFECTS OVER LAND, TS 26W WILL STEADILY WEAKEN WITH DISSIPATION ANTICIPATED NO LATER THAN TAU 48. MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN FAIR AGREEMENT THEREFORE THERE IS MEDIUM OVERALL CONFIDENCE IN THE JTWC FORECAST TRACK. THE 011800Z ECMWF (EPS) AND GFS (GEFS) ENSEMBLES ARE ALSO IN FAIR AGREEMENT AND SUPPORT THE JTWC TRACK PHILOSOPHY. ALL ENSEMBLE SOLUTIONS INDICATE STEADY WEAKENING WITH A WEAK 20-25 KNOT SYSTEM TRACKING ALONG THE SOUTHERN COAST OF CHINA THEN FURTHER WEAKENING AND EVENTUAL DISSIPATION. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM// NNNN