


Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
934 FXPQ50 PGUM 180758 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 558 PM ChST Sat Oct 18 2025 .Marianas Synopsis... Moderate to fresh trades prevail in the region. Satellite imagery and Doppler radar indicate slow-moving stratiform rain in western Guam waters. Buoys and altimetry show seas are 5 to 8 feet in the area. && .Discussion... A broad surface trade-wind trough enhanced by the TUTT upstream, brought elevated rainfall amounts and lightning to the Marianas and adjacent waters for much of the afternoon earlier today, with sporadic but heavy showers and thunderstorms still expected until midnight, bringing along strong gusts. Shower and thunder coverage will then decrease considerably after, followed by another albeit minor trough to bring patchy showers and some thunderstorms early next week, followed by a drier cycle for the rest of the forecast period. && .Marine... Combined seas of 6 to 8 feet will stay elevated and choppy through at least the first half of next week, as northerly swells and trade swell continue to interact and mix in. Seas are then expected to decrease once these swells weaken, especially the northerly swell, which is expected to dissipate by the second half of next week. A moderate risk of rip currents is expected along north and east facing reefs of the Marianas for much of the forecast period. Surf is likely to taper down along all reefs once the aforementioned swells weaken, potentially allowing the rip risk to drop to low along north facing reefs by the second half of next week. && .Eastern Micronesia... Majuro: The main change to the forecast was at Majuro, where rainfall coverage was increased to widespread shower coverage with locally heavy rainfall also included. This was due to a fairly stout surface trough that`s currently moving through that region. Satellite analysis shows persistent shower development with cloud top temperatures occasionally surpassing -75 deg. C. This trough will move off to the west by Sunday night though, decreasing rainfall potential briefly, before the next trough moves in Monday night with rainfall potential increasing once again. Pohnpei and Kosrae: Isolated showers will continue through Sunday evening. Then, as the Majuro trough approaches, rainfall potential increases by Monday, continuing through at least the middle of the week as the models show additional troughs crossing the Date Line, with streamline and satellite analysis confirming this as well. Winds and Seas: Gentle to moderate winds by Sunday at Majuro will reach Kosrae Monday and Pohnpei Tuesday. Seas of 4 to 6 feet will increase a foot or so towards the middle of next week. && .Western Micronesia... Satellite this afternoon reveals a quieter pattern across far western Micronesia, with a surface ridge extending southeast across the Republic of Palau, passing south of Koror. There is a weak surface trough just northeast of this feature, with the axis oriented southeast to northwest between Palau and Yap, extending toward Tropical Depression Fengshen. However, the associated convergence and convection has shifted northwest away from the region, with only isolated showers seen over Yap and Palau coastal waters. Extensive upper-level cloud cover persists over Yap from prior deep convection, and skies will remain mostly cloudy for much of tonight. Conditions are similarly quiet over Chuuk, with a surface ridge just south of Weno and a broad trough just west to northwest of coastal waters, moving away. Similarly weak, transient features will be the main focus for any weather across the region for much of the forecast period. Stronger convergence ahead of a broad trade-wind trough will increase showers near Yap around Sunday night. This trough looks to amplify slightly as it moves into far western Micronesia around Monday night, increasing showers more directly over Yap and Palau through midweek. A broad ridge behind this disturbance will allow for quieter conditions come Thursday. Chuuk will continue to see isolated showers through Sunday with scattered showers beginning to build Sunday night, due to increasing convergence along the backside of the aforementioned broad trough. A slightly stronger trough looks to arrive during the midweek, with weaker, more transient features in between. Benign marine conditions continue with little change in the forecast. Latest altimetry data continues to indicate combined seas around 3 to 5 feet near Palau and Yap and around 4 to 6 feet near Chuuk, comprised of a primary northeast swell. Similar sea conditions will prevail for Palau and Yap for much of the forecast period, with seas gradually diminishing by a foot or so through the week as the incoming trade swell relaxes. Chuuk will see an increase in winds and seas around midweek, as trade winds and associated swell begin to pick up. Winds will remain light to moderate for Palau and Yap through the period. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Montvila East Micronesia: Doll West Micronesia: Decou