05W(GAEMI) forecast to reach CAT 3 US by 96H// 04W peaking near HAINAN within 36h//INVEST 93W// 2009utc

JTWC IS ISSUING 6HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON 04W AND 05W

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A SLOWLY CONSOLIDATING SYSTEM IN THE SOUTH CHINA SEA (SCS) WITH FORMATIVE, FRAGMENTED BANDS LOOSELY FEEDING INTO A BROAD, MOSTLY OBSCURED, AND ILL-DEFINED LOW LEVEL CIRCULATION (LLC). THE INITIAL POSITION, EXTRAPOLATED FROM THE CURRENT STORM MOTION, IS PLACED WITH LOW CONFIDENCE BASED ON THE LLC IN THE MSI LOOP. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON OVERALL ASSESSMENT OF AGENCY AND OBJECTIVE DVORAK ESTIMATES AND CONSISTENT WITH THE SUSTAINED 6-HR CONVECTIVE SIGNATURE. THE INITIAL POSITION AND ESTIMATE ARE ALSO CONSISTENT WITH SURFACE WIND OBSERVATIONS IN THE SCS. ENVIRONMENTAL ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH WARM SST AND MODERATE EQUATORWARD OUTFLOW OFFSET BY MODERATE VERTICAL WIND SHEAR.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TD 04W IS EXPECTED TO CONTINUE TRACKING WEST-NORTHWESTWARD UNDER THE STEERING INFLUENCE OF THE STR TO THE NORTHEAST, BECOMING MORE NORTHWESTWARD AFTER TAU 24 AS THE STR IS WEAKENED BY A MID-LATITUDE TROUGH DIGGING IN FROM THE NORTHWEST. TD 04W WILL MAKE LANDFALL OVER HAINAN SHORTLY AROUND TAU 30, CROSS THE GULF OF TONKIN, THEN WILL TRACK INTO SOUTHERN CHINA JUST BEFORE TAU 72. THE MARGINALLY FAVORABLE ENVIRONMENT WILL PROMOTE A MODEST INTENSIFICATION TO A PEAK OF 45KTS BY TAU 24. AFTERWARD, LAND INTERACTION WITH HAINAN AND SOUTHERN CHINA WILL PRIMARILY ERODE THE SYSTEM TO DISSIPATION BY TAU 96.

MODEL DISCUSSION: THE LIMITED NUMERICAL MODELS ARE IN GOOD AGREEMENT, GRADUALLY SPREADING OUT TO 217NM BY TAU 72 THEN BECOME ERRATIC AS THEY LOSE THE WEAKENED VORTEX. IN VIEW OF THIS AND GIVEN THE STRAIGHT- FORWARD STEERING MECHANISM, THERE IS MEDIUM CONFIDENCE IN THE JTWC TRACK FORECAST UP TO TAU 72, THEN LOW CONFIDENCE AFTERWARD.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL DEPRESSION (TD) 05W (GAEMI) AS CONTINUING TO STRUGGLE TO BECOME VERTICALLY ALIGNED. THE LOW-LEVEL CIRCULATION CENTER (LLCC) CONTINUES TO BE PARTIALLY EXPOSED AND OFFSET TO THE EAST OF THE DEEP CONVECTION. EASTERLY SHEAR IS EVIDENT IN THE ANIMATED MSI, WITH MODELS SUGGESTING AROUND 20 KTS CURRENTLY. ENVIRONMENTAL ANALYSIS INDICATES THAT 05W IS IN A MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY GOOD POLEWARD OUTFLOW ALOFT ENHANCED BY A TUTT CELL LOCATED TO THE NORTHEAST OF THE SYSTEM, WARM (30-31 C) SEA SURFACE TEMPERATURES, OFFSET BY THE MODERATE (20 KTS) EASTERLY SHEAR. THE VERTICAL ALIGNMENT SEEMS TO BE THE MAIN HINDRANCE IN TERMS OF INTENSIFICATION AT THE MOMENT. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC SEEN IN THE ANIMATED MSI. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TD 05W IS FORECAST TO CONTINUE TRACKING NORTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF THE STR THROUGH TAU 36. AROUND TAU 36 THE SYSTEM IS FORECAST TO TAKE A MORE NORTH-NORTHWESTWARD TRACK AS THE STR REORIENTS TO A NORTH-SOUTH ORIENTATION IN RESPONSE TO A MID-LATITUDE TROUGH PROPAGATING OVER THE KOREAN PENINSULA. 05W IS ANTICIPATED TO CONTINUE ALONG THIS TRACK THROUGH TAU 96 WHEN RIDGING OVER EASTERN CHINA TAKES OVER THE STEERING AND DRIVES THE SYSTEM MORE WESTWARD. CONCERNING THE INTENSITY FORECAST, 05W IS FORECAST TO GRADUALLY INTENSIFY OVER THE NEXT 72 HOURS TO AROUND 70 KTS DUE TO WARM SST AND HIGH OHC VALUES BUT WILL BE HINDERED BY HIGH VERTICAL WIND SHEAR VALUES (25-30 KTS) DURING THE PERIOD. AFTER TAU 72, VWS VALUES ARE EXPECTED TO DROP DRASTICALLY AND WILL ALLOW FOR MORE ROBUST INTENSIFICATION. NEAR THE END OF THE FORECAST PERIOD, 05W IS FORECAST TO BEGIN WEAKENING WITH COOLER SST AND LAND INTERACTION BEGINNING TO BE A FACTOR.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 72, WITH A 250 NM CROSS-TRACK SPREAD AT TAU 72, WHICH INCREASES TO AROUND 300 NM AT TAU 120, WITH ALL JTWC CONSENSUS MEMBERS TRACKING THE SYSTEM WEST OF OKINAWA. WITH THE EXCEPTION OF UKMET, ALL GUIDANCE SUGGESTS A TRACK EAST OF TAIWAN AS WELL. THIS LENDS HIGH CONFIDENCE TO THE JTWC TRACK FORECAST THROUGH TAU 72, AND MEDIUM CONFIDENCE THEREAFTER. INTENSITY GUIDANCE AGREES THROUGH TAU 72 AS WELL, DEPICTING A STEADY INTENSIFICATION PHASE TO AROUND 60-75 KTS. AFTER TAU 72, THE GUIDANCE SPLITS WITH COAMPS-TC CALLING FOR A PEAK INTENSITY OF 115 KTS WHILE GFS AND HAFS-A CALL FOR A MORE MODEST PEAK OF AROUND 80-90 KTS. THE JTWC INTENITY FORECAST IS PLACED BETWEEN THE TWO POSSIBILITIES AND IN ASSESSED WITH MEDIUM CONFIDENCE THROUGH THE FORECAST PERIOD.