Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
355 FXPQ50 PGUM 020902 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 702 PM ChST Tue Sep 2 2025 .Marianas Synopsis... Satellite imagery shows mostly cloudy skies, while the radar shows isolated showers. Ritidian buoy shows sea heights of near 3 feet. Winds are gentle to moderate with a few fresh gusts. So far today, 0.80 inches of rain has fallen at the airport. && .Discussion... A trough is moving towards the Marianas. This will bring scattered to numerous showers and isolated thunderstorms to the region through the middle of the week. Radar indicates that the showers associated with this trough in the nearby waters are diminishing. However, showers are expected to pick back up overnight. Model guidance suggests the peak of the showers will be tonight into early Wednesday morning. Once this trough passes, a ridge is anticipated to build in, bringing in some drier more pleasant weather. && .Marine... Combined seas of 3 to 5 feet are expected to fall to between 3 and 4 feet across the region by the end of the week, due to the weakening of the trade winds and swell. There is a moderate risk of rip currents along east facing reefs. Surf is expected to fall a foot by Thursday. Surf is expected to remain below hazardous levels through the rest of the week. There is also a moderate risk if lightning through Wednesday. && .Eastern Micronesia... A surface trough stretches from Chuuk to north of Pohnpei this afternoon, with streamlines and MIMIC water vapor imagery suggesting a new surface trough is trying to form between Pohnpei and Kosrae, as MIMIC water values increase slightly to near 2.5 inches, with some mild "bending" in the streamline analysis. This is likely due to a ITCZ (Inter-Tropical Convergence Zone) fragment that has surged across the Date Line as expected, accompanied by a lead surface trough that`s located east of Majuro. However, as the ITCZ temporarily strengthens, moisture flux westward is occurring, helping to explain the genesis of the Pohnpei/Kosrae trough. This trough then gets overtaken by the Majuro trough by late Thursday night. What this means is there`s an increasing rainfall potential from east to west over the next few days as these features interact as they pass through Eastern Micronesia on their westward journey. Following the Majuro trough passage, rainfall coverage is anticipated to drop back to isolated shower coverage, with the best rainfall potential being Wednesday and Wednesday night at Majuro...Wednesday night and Thursday at Kosrae...and Thursday and Thursday night at Pohnpei. As for marine conditions, mainly light to gentle winds will prevail, but they could briefly become moderate from time to time. Seas of 3 to 5 feet will build a foot into the 4 to 6 foot range Thursday following trough passage, continuing through the weekend and into next week. && .Western Micronesia... A broad surface trough continues to bring patchy showers and some thunderstorms to Palau and Yap overnight (with gustier heavy showers at Yap), followed by another drier cycle to last for the rest of the week. At Chuuk, a mostly quiet pattern with gentle to moderate easterlies is still expected to persist through Thursday night, followed by a trade-wind surge moving in from the east, bringing elevated shower and thunderstorm potential towards the end of the week. Combined seas of 3 to 4 feet near Palau and Yap are expected to remain as such the next few days, as trade swell remains fairly weak. Combined seas of 3 to 5 feet near Chuuk are expected to remain as such for much of the forecast period, comprised mainly of an easterly swell. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Bowsher East Micronesia: Doll West Micronesia: Montvila