Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
248 FXPQ50 PGUM 041012 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 812 PM ChST Sat Oct 4 2025 .Tropical Systems Update... Invest 94W is now the subject of a Tropical Cyclone Formation Alert, meaning tropical cyclone development is likely within 24 hours. The latest location for 94W is 23.8N and 143.3E, well north of the Marianas and east-southeast of Iwo To. Maximum sustained winds are 23 knots and the system is moving north-northwestward at 4 kt. For more information on Invest 94W, see bulletins issued by JTWC under WMO headers WTPN21 and ABPW10 PGTW. && .Prev discussion... /issued 524 PM ChST Sat Oct 4 2025/ Marianas Synopsis... Satellite imagery shows mostly cloudy skies, while radar imagery shows a few island effect showers near northern Guam. Buoy data shows sea heights of about 2 to 3 feet. Altimetry did not get a good pass near the islands today. Discussion... The Marianas is in the inflow convergence region of Invest 94W. Being in this region means as 94W strengthens so to will the change of showers increase. The island convection that was in the forecast has been removed due to the expected increase in cloud cover. Showers are expected to increase as Tuesday approaches. A trough is anticipated to pass over the Marianas then bring in high-end scattered showers and isolated thunderstorms to the region. Once this trough passes, pleasant weather may return. Marine/Surf... Combined seas of 2 to 4 feet and light to gentle winds are expected through at least Wednesday. There is a low risk of rip currents along all reefs through at least Wednesday. There also remains a moderate risk of lightning through at least Wednesday. Tropical Systems... Invest 94W is centered over the far northern CNMI near 23N143E. 94W is now rated as medium, meaning that development into a significant tropical cyclone is expected, but not within the next 24 hours. 94W is expected to continue to move west over the coming days as it continues to consolidate. Invest 94W will be monitored closely for the next few days. For more information on Invest 94W, see bulletins issued by JTWC under WMO header ABPW10 PGTW. Eastern Micronesia... A dry pattern has moved into Kosrae and Pohnpei for tonight, while Majuro is seeing scattered showers and isolated thunderstorms as a trade-wind trough approaches from the east. The Inter-Tropical Convergence Zone (ITCZ) has drifted north allowing a drier pattern to move into Pohnpei and Kosrae. This dry pattern will be short-lived as the ITCZ, though weaker, is expected to drop south while a weak trade-wind trough moves through. Scattered showers and isolated thunderstorms are expected to move into Kosrae Sunday and into Pohnpei Sunday night. Increased convection will continue at Pohnpei through most of next week as weak troughs continue to traverse the area. POPs (Probability of Precipitation) will range from 30 to 50% as the ITCZ wavers north and south. Kosrae will see a drier pattern return around the end of next week as the ITCZ moves out of the state. Majuro will see scattered showers and isolated thunderstorms through tonight as a trade-wind trough moves through and interacts with the ITCZ. For Sunday, scattered showers will continue, though will decrease. There will be a brief dry period for Sunday night, followed by another trade-wind trough bringing increased showers Monday and Monday night. By Tuesday, a dry pattern returns to Majuro and continues through the end of the week. Marine conditions are expected to remain fairly benign, with light to gentle winds and combined seas of 5 feet or less continuing through most of next week. Western Micronesia... Satellite imagery shows a broad trough gradually moving into Chuuk this afternoon. Late tonight and into Sunday, models continue to indicate some development with this feature as it slowly drifts northwest over the next day or so as a tropical disturbance. Unsettled weather is in store for Chuuk through Sunday or Sunday night, until the disturbance pulls away to the northwest, then scattered showers will continue through much of the upcoming week as a fragment of the ITCZ lifts northwest into the area. Meanwhile, patchy showers and light to gentle west to southwest winds over Yap and Palau are expected over the next couple days. Then, conditions begin to deteriorate Monday and Tuesday as distant Invest 94W and the aforementioned disturbance in central Micronesia support a southwest monsoon pattern over the region. Showers are expected to become numerous at times, mainly for Yap, with locally heavy showers possible. Scatterometry and altimetry data indicates benign marine conditions, light to gentle winds and combined seas of around 2 to 4 feet across the region. A pulse of southwest swell looks to build across Palau waters Monday, driven by a developing monsoon-like pattern, but no marine or surf hazards are expected at this time. Winds will remain mostly light to gentle, becoming moderate at times as the monsoon- like pattern strengthens. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Tropical Systems Update: Cruz Marianas: Bowsher East Micronesia/Tropical: Kleeschulte West Micronesia: Cruz