####018005078#### AXPQ20 PGUM 072148 TWDPQ Tropical Weather Discussion National Weather Service Tiyan GU 748 AM ChST Thu Jun 8 2023 Tropical Weather Discussion for the Western North Pacific between the Equator and 25N from 130E to 180. The following information is based on recent satellite imagery/data, weather observations, radar, and meteorological analysis. ...SIGNIFICANT/SPECIAL FEATURES... TROPICAL CYCLONES... As of 7am, Tropical Storm (TS) Guchol was centered 600 miles northwest of Yap and 865 miles west-northwest of Guam, moving toward the west- northwest at 8 mph. Latest geostationary and microwave data shows core convection has not been able to fully wrap around the western side of Guchol. If Guchol can complete this westward wrap of core convection, it is likely to become a typhoon later today. Monsoonal showers along the far southern periphery of Guchol have largely lifted out of Palau and Yap. For more information please refer to bulletins from the Joint Typhoon Warning Center under WMO header WTPN31 PGTW and from the National Weather Service under WMO header WTPQ31 PGUM. ...OTHER WEATHER SYSTEMS... MONSOON TROUGH... TS Guchol anchors the eastern extent of the monsoon trough that spans much of South East Asia. TUTT... The TUTT (Tropical Upper Tropospheric Trough) curves westward through 18N180 to a pair of TUTT cells, one near Wake Island and another centered well north-northeast of Saipan near 19N147E. Divergent flow south of these TUTT cells is enhancing convection across open waters southeast and east of the Marianas between 148E to 175E. The Saipan TUTT cell is boosting Guchol's outflow on the eastern side. SURFACE TROUGHS AND ATTENDANT CIRCULATION... A lengthy, northeast-to-southwest oriented surface trough sits east of the Marianas...just east of 150E. Overnight scatterometer data shows a pocket of strong trade winds along the far northern extent of this trough. A circulation, JTWC Invest 90W, rests along the southern extent of this surface trough. 90W appears to have backed eastward since yesterday based on 12 hr scatterometer continuity and long- satellite loops. Convection is still displaced to the eastern side of these features, courtesy of an upper-level trough digging down from the Saipan TUTT cell. This upper-level trough is also limiting the forward (westward) progression of the surface trough and 90W. ...ITCZ... The ITCZ (Inter-Tropical Convergence Zone) is looking a bit more definitive this morning with convergent flow snaking its way westward through the dateline and Kiribati at 2N, through southern Pohnpei State to end south of Chuuk Lagoon near 3N150E. Clusters of showers are focusing along troughs embedded within this ITCZ south of 6N. ...DISCUSSION... TS Guchol continues to strengthen. Guchol is likely to become a typhoon later today if it can wrap core convection westward in earnest. If this process is a bit slower, it will probably become a typhoon tonight or early Friday. Guchol will continue to roam the open waters of the Phillipines Sea with a classic recurve scenario into the midlatitudes this weekend into early next week. The northward lift of Guchol will continue to pivot the monsoon trough northeastward, allow a gentle trade-wind regime to edge into Palau and Yap early next week. The surface trough and circulation east/southeast of the Marianas will continue to trek ever so slowly to the west. Models still advertise this north-to-south oriented surface trough to split, with the far northern extent peeling into some sort of ill-defined, low- level circulation north of 20N while 90W wanders around somewhere south of Guam. Both entities have bleak futures as they likely wash out in the trade flow. There is still an inkling of support that residual vorticity from 90W trudges westward and links with trailing vorticity to reassemble a low-level circulation somewhere near Palau towards the middle of next week. This would allow it to tuck in against the established South East Asia monsoon pattern and potentially spin up. This is still several days away so will monitor closely. The MJO, currently centered over the western Indian Ocean is likely to become active again across the West Pacific basin late June and early July. This may bring a more bonafide TC threat to Micronesia, especially if a notable westerly wind burst can develop. The ITCZ is still forecast to revive the second half of the week as low-level convergence picks up and a slight surge in the trade flow occurs. This looks to bring a better chance of showers to central and eastern Micronesia south of 12N. Disturbances riding along the ITCZ may be enhanced by additional TUTT cell activity to the north. Vorticity from these features may mesh into far western Micronesia late next week to potentially foster some sort of TC development near or west of Palau. $$ Bukunt