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Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
367 FXPQ50 PGUM 270643 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 443 PM ChST Thu Jun 27 2024 .Marianas Synopsis... Partly cloudy skies with isolated showers and gentle to moderate trade winds prevail across the Marianas this afternoon. Guam is seeing occasional strong gusts. Ritidian buoy shows seas near 5 feet while altimetry shows seas in the 4 to 6 foot range. && .Discussion... A dry trade-wind pattern remains in place across the Marianas this afternoon. Over the weekend, a trade-wind trough, currently seen near 170E, is expected to move through the Marianas, with a second trough seen a little farther south not far behind the first trough. As the first trough moves through the Marianas, upper-level divergence, associated with a TUTT (Tropical Upper-Tropospheric Trough) cell expected to be to the northwest of the Marianas, will create a marginally favorable environment for thunderstorms to develop across the Marianas. Therefore, have a slight chance of thunderstorms in the forecast for Saturday and Saturday night. By Sunday, the second trough will arrive, farther south, affecting Guam and possibly Rota. At the same time, the TUTT cell is expected to move out, with an upper-level ridge replacing it, putting the Marianas under a band of convergence aloft. This will inhibit thunderstorm development. Based on this, expect low-end scattered showers across Guam and Rota Sunday and Sunday night with no thunderstorms expected. Latest model guidance continues to show the development of a west- east oriented trough developing across Micronesia, west of Pohnpei, with several weak circulations popping up here and there over most of next week. It currently looks likely that the bulk of convection will remain south of the Marianas. However, due to the vicinity of another TUTT cell possibly producing weak upper-level divergence over the Marianas for several days, maintained mostly cloudy skies with a slight chance of thunderstorms for most of next week. && .Marine... Combined seas of 4 to 6 feet will continue into the weekend, then slowly subside to between 3 and 5 feet Sunday. The seas will be mainly comprised of a moderate trade-wind swell. This swell will maintain surf high enough to produce a moderate risk of rip currents along east facing reefs through at least the middle of next week. The rip current risk will be low along all other reefs. Gentle to moderate trade winds are expected through the beginning of next week. && .Eastern Micronesia... A pair of westward-moving surface troughs are focusing showers near Pohnpei and atop the western chain of the Marshalls. A cluster of thunderstorms has been evident south of Kwajalein through the afternoon, but, for the RMI, convection is slowly clearing out as it treks west. Latest CIMSS MIMIC TPW shows a wide band of increased moisture with PWATs well over 2in across Pohnpei and Kosrae. A drier air mass is moving into the Marshalls for the short term, but more moisture will eventually move into the region. For most of the region, the forecast is generally on the wetter side, reflecting the increased regional moisture and the anticipation of a more active ITCZ pattern taking shape over the weekend. Early in the weekend, showers are expected to stay between 3-4N and 8N, then gradually lift northward by early next week, perhaps up to 12N. Seas will be fairly benign with no hazards anticipated other than localized effects from areas of heavier showers or thunderstorms. Winds will be mostly moderate, occasionally fresh with seas staying between 3 and 5 feet, maybe up to 6 or 7 feet just east of the Marshalls. Wave model data shows a dominant easterly swell though Pohnpei and Kosrae will see some southeasterly swell from southeasterly trades across the South Pacific. && .Western Micronesia... A weak trade-wind convergence pattern is maintaining scattered showers and a few thunderstorms across the area, mostly near Yap and farther south of Chuuk. For Palau, conditions have quieted with only a few showers. A moderate trade-wind pattern will dominate the region the next couple of days before winds really begin to weaken over the weekend. Have largely maintained scattered showers (30-50 POPs) for much of the forecast for all 3 locations based on the wetter pattern models depict from weakly convergent trades or passing trade-wind troughs. Subsequent forecast issuances will have the opportunity to better identify short-term drier spells that are obscured more than a day in advance. Heading into next week, a weak surface wind pattern may at times allow some weak circulations to briefly appear but models show nothing of significance taking root beyond a weak flow pattern. Similar to eastern Micronesia, seas will be subdued, generally between 3 and 5 ft with seas up to 6 ft north of Yap and Chuuk. Currently, no marine hazards are anticipated in the next few days. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Kleeschulte Micronesia: Aydlett