


Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
538 FXPQ50 PGUM 010744 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 544 PM ChST Tue Jul 1 2025 .Marianas Synopsis... Satellite imagery and radar show isolated showers for Guam and Rota and scattered showers for Tinian and Saipan. Altimetry shows combined seas of 3 to 5 feet, while Ipan and Ritidian buoys show heights of 3 to 4 feet. && .Discussion... Scattered showers are seen just outside the Marianas waters. These showers are anticipated to build in overnight for much of CNMI, Guam is expected to remain in a clearer region. A break in the monsoon trough will give way to a drier next few days. Showers are anticipated to pick back up around the end of the workweek. Over the weekend, showers are anticipated to be minimal. && .Marine... Benign sea conditions are anticipated throughout the forecast period. Winds are expected to be light to gentle. Surf is the highest along east facing reefs. An incoming southwesterly swell is anticipated to arrive over the weekend. This may increase surf and rip current risk along south and west facing reefs. The risk of rip currents remains moderate along east facing reefs. && .Tropical systems... JTWC`s (Joint Typhoon Warning Center) Invest 90W, currently showing a defined circulation center, but is roughly located well north- northeast of Saipan near 22.5N 148.2E, moving northward. Numerous showers and isolated thunderstorms are found to the east of the invest. 90W is now rated low, meaning it is expected to develop, but not expected to become a significant tropical cyclone within the next 24 hours. Although a closed circulation is not seen now, 90W is becoming more organized, with a TUTT cell near 21N145E providing divergent flow in the upper levels. Models do favor 90W developing into a more organized circulation as it continues north. For more information on Invest 90W, see bulletins issued by JTWC under WMO header ABPW10 PGTW. && .Eastern Micronesia... For now, the Inter-Tropical Convergence Zone (ITCZ) has weakened a bit, with less convection seen along the boundary. There is a flare up of convection with a trade-wind trough that is moving toward Kosrae. This trough looks to bring increased convection to Kosrae later this evening. Another weak trough is seen approaching Pohnpei and is expected to bring low-end scattered showers and possible thunderstorms to Pohnpei by midnight. Otherwise, the ITCZ is expected to strengthen a bit, with increasing showers spreading across the region. An overall unsettled pattern looks likely for the region as the ITCZ strengthens and weak trade-wind troughs move through. There will be brief periods of isolated showers through the week due to the wavering of the ITCZ and in between troughs moving through. No changes were made to the marine forecast. Combined seas of 5 to 7 feet at Majuro slowly subsiding over the next few days, dropping to between 3 and 5 feet for the weekend. Seas of 4 to 6 feet for Kosrae and Pohnpei could reach 5 to 7 feet tonight into Wednesday before subsiding to between 3 and 4 feet for the weekend. Gentle to moderate winds are expected through the week for Kosrae and Majuro, with gentle to moderate winds becoming light to gentle for Pohnpei Wednesday night. && .Western Micronesia... The wet, southwesterly monsoon pattern looks to continue for tonight with rounds of heavier showers and thunderstorms for both Yap and Palau. Could see fresh to potentially strong gusts with the bursts of showers. A surface ridge will try to creep west and may push the edge of the monsoon flow to the north and west of Palau and Yap, with generally isolated to low-end scattered showers expected through the end of the week. Through the weekend into early next week, may see the ridge break down over the region and a slow return to a wetter, monsoon-like pattern. Outside of gusty winds and choppy seas near heavier showers and thunderstorms, fairly benign marine conditions expected, with seas 3 to 5 feet and gentle to at times moderate winds will diminish slightly over the coming days as the monsoon swell and winds decrease. By late weekend into early next week, a longer-period northwest swell generated by a possible distant tropical cyclone developing northeast of the Philippines could build into the region, increasing seas ans surf. For Chuuk, a surface trough lifting northwest along the leading edge of a building ITCZ will bring increasing showers over the coming days. Expect isolated showers this evening to become scattered after midnight. High-end scattered to numerous showers and isolated thunderstorms are expected Wednesday through Thursday as the aforementioned features pass through. While coverage looks to diminish beyond Thursday as the trough pushes away and the ITCZ diminishes, are still expecting scattered showers and isolated thunderstorms into the weekend as subtle surface features pass through and weak east-southeast flow linger. Gentle to moderate winds are expected through Thursday. Fresh to potentially strong gusts are possible near heavier showers and thunderstorms as well. Winds look become light to gentle by Friday as the trough pushes west. Seas of 4 to 6 feet will be possible through Thursday night with the disturbance pushing through, then lowering around 2 feet by the weekend. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Bowsher East Micronesia: Kleeschulte West Micronesia: Slagle