Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
122 FXPQ50 PGUM 130739 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 539 PM ChST Thu Nov 13 2025 .Marianas Synopsis... A minor trough brought by gentle to moderate trades is entering Guam`s eastern waters. The buoys show seas are around 4 to 5 feet. && .Discussion... After the passage of a minor surface trough that will bring low-end scattered showers to Guam late tonight, a drier trade-wind regime will continue across the Marianas for much of next week. Winds are likely to begin increasing into the weekend, potentially becoming breezy early next week as the pressure gradient increases between the mid-latitudes and the tropics. && .Marine... Combined seas of 4 to 5 feet are expected to persist through Friday night, before slowly increasing thereafter as trade swell and winds pick up. A moderate risk of rip currents is expected along north and east facing reefs of the Marianas through Friday, before tapering down to low along north facing reefs beginning Friday night. Surf may rebuild along north and east reefs beginning early next week as trade swell strengthens. && .Eastern Micronesia... Moderate trades and patchy showers are seen across much of the area this evening. Afternoon surface analysis shows a weak convergence boundary extending west-east between Pohnpei and Majuro roughly along the axis of peak precipitable water, as seen in recent Blended TPW. A trough is currently passing by the Ratak Chain of the RMI and will continue west the next couple of days. In the wake of this trough, models show ITCZ convection flaring up between 3N and 8N from Pohnpei eastward. Showers and thunderstorms will develop in westward-drifting clusters from time to time through the weekend. Early next week, a cutoff upper-level low may set up over the far northern or northwestern RMI, possibly in a favorable position to excite ITCZ convection over Kosrae State or portions of the RMI. This interaction could be manifest by pockets of very heavy rainfall or brief, but very strong wind gusts. Given that this scenario is still 4 days out, will watch subsequent model trends for any adjustments on the upper- level features and timing of convection. Latest altimetry shows seas of 4 to 6 ft south of 5-6N and seas of 5 to 8 ft to the north of 6N and east of the Marshalls. Seas will subside 1 to 2 ft this weekend but will then increase next week as a trade-wind surge builds across the region, especially along and north of 9N. While no marine hazards are currently anticipated through the weekend, conditions will step closer to surf and small craft hazards next week. The Pohnpei buoy shows a distinct N swell in the 10-14sec period band, and based on that buoy, have bumped up the north swell magnitude a little above wave model guidance. Additionally, the combined seas were raised a little above guidance to better initialize with recent altimetry data. && .Western Micronesia... Satellite observations show isolated showers across Palau and Yap, in addition to scattered showers and isolated thunderstorms just outside of the coastal waters of Weno. Altimetry data shows combined seas generally between 4 and 6 feet across the region with a few 7 foot seas west of Weno. Much quieter conditions are present across the region today. Isolated showers are currently observed over Palau, Yap, and Weno. Scattered showers and isolated thunderstorms are seen just outside of Weno`s coastal waters and are expected to move into Weno this evening. Scattered showers will persist the next several days across Chuuk State. PoPs were trended downward for Palau and Yap through the rest of the week. The weak circulation that was Invest 91W has weakened and the JTWC closed 91W early this morning. Scattered showers and isolated thunderstorms are still expected across Palau through the week as the Near Equatorial Trough (NET) continues to interact with the weak circulation south of Palau and trade-wind convergence to the east. Yap will see a brief chance for scattered showers on Friday with isolated showers through the weekend. Overall, only minor edits were made to the Marine forecast. Benign sea conditions are expected to continue through Monday across western Micronesia. Combined seas will be 4 to 6 feet through the weekend and then seas look to start increasing Monday night into Tuesday across Chuuk State. The ECMWF shows a strong trade-wind swell move into the region towards the middle of next week. The GFS has slightly lower sea heights, but has trended closer to the ECMWF solution over the last few runs. There will be the potential for hazardous marine and coastal conditions across Chuuk towards the middle of next week and Yap towards the end of the week. Those with marine interests in western Micronesia should monitor forecasts for additional details over the coming days. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Montvila East Micronesia: Aydlett West Micronesia: Williams