Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
031 FXPQ50 PGUM 170639 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 439 PM ChST Tue Jun 17 2025 .Marianas Synopsis... A surface trough is pushing through the Marianas this afternoon with showers near Guam and Rota, and drier conditions across Tinian and Saipan. A few thunderstorms were seen on satellite today, primarily south of Guam. A TUTT cell remains west of Guam, near 140E, with its peripheral effects waning across the Marianas. Combined seas are around 2 to 3 feet at the Ipan and Ritidian buoys. && .Discussion... A surface trough pushing through the Marianas today will move west of the islands overnight, with moisture trailing behind it a little longer. Shower coverage will taper with a drier end of the week. Winds the next few days should keep daytime island-heating showers near Guam to a minimal, or displaced just over the western coastal waters. The TUTT cell remains in the vicinity west of Guam along 140E, but its peripheral effects are decreasing. Moderate trades the next few days will subside this weekend. Longer-range models indicate a bit of a pattern change for next week with lighter winds, more moisture and a still-active TUTT pattern across the CNMI. While no large scale features are present in the long range, conditions across the Marianas could feel more appropriate for the wet season. && .Marine... Marine conditions will remain benign for the remainder of the week, with only a small increase in seas the next few days. Combined seas of 2 to 3 feet will build to between 3 and 5 feet by Thursday as the trade winds and swell increase for the last half of the week. Winds and seas will subside again this weekend. There will be a moderate risk of rip currents along east facing reefs Thursday and Friday. && .Eastern Micronesia... Convection has decreased significantly across eastern Micronesia as the Inter-Tropical Convergence Zone (ITCZ) became fragmented, with little convergence seen over the forecast points. Latest model guidance continues the trend of a weakening ITCZ as it slowly drifts west. There are a few trade-wind troughs moving through the region. These troughs will bring periodic scattered showers and isolated thunderstorms to Majuro tonight and to Kosrae tonight and Wednesday. Otherwise, a fairly dry pattern looks to be in store for eastern Micronesia through the end of the week. Latest guidance does show another ITCZ developing across the region over the weekend, bringing increased showers to all three forecast points. Due to the uncertainty of the position and strength of this ITCZ, kept probabilities of showers in the 30% range. Fairly benign marine conditions will continue through the weekend. Combined seas of 4 to 6 feet for Kosrae and Pohnpei will subside to between 3 and 4 feet for the weekend. Seas of 5 to 7 feet for Majuro will also subside, reaching 4 to 5 feet for the weekend. Gentle to moderate winds will become light to gentle for Kosrae and Pohnpei Wednesday night and for Majuro Thursday night. && .Western Micronesia... Benign conditions are expected tonight for Palau, however, scattered showers and isolated thunderstorm will be possible for Yap as a trade trough passing to the north may clip the island, with the Tropical Upper-Tropospheric Trough (TUTT) cell to the north and west enhances lift across the region. Otherwise, isolated trade showers expected for Yap in the trough`s wake on Wednesday. Showers and thunderstorm chances increase beginning Wednesday for Palau and Wednesday night at Yap as a Near-Equatorial Trough (NET) develops near to over the main islands of Palau, turning the flow slightly south and enhancing the moisture, convergence and lift over the region through the weekend. Showers could become high-end scattered to numerous and locally heavy for Palau Wednesday night through Thursday night. Over towards Chuuk, the Inter-Tropical Convergence Zone (ITCZ) is becoming fragmented. A weak trade disturbance along the ITCZ could bring low-end scattered showers through Wednesday morning, with isolated trade showers then expected through Thursday. Model guidance shows the ITCZ re-organizing across the region toward the end of the week as it lifts north over Chuuk, enhancing the convergence and lift and bringing wetter conditions beginning Thursday night and continuing through the weekend. Combined seas of 2 to 4 feet over Yap and Palau waters and 3 to 5 feet near Chuuk will continue for the next couple of days, increasing a foot or so around Wednesday night or Thursday as trade swell builds slightly, the lowering 1 to 2 feet towards the weekend as the swell subsides. Gentle to moderate winds for Yap and moderate winds with fresh to at times strong gusts for Palau will decrease and become light to gentle for Palau by Thursday and generally gentle for Yap by Thursday night as the NET develops creeps north. Meanwhile, gentle to moderate winds across Chuuk will become light to gentle by the weekend as the ITCZ creeps north. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Aydlett East Micronesia: Kleeschulte West Micronesia: Slagle