Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
290 FXPQ50 PGUM 190731 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 531 PM ChST Thu Sep 19 2024 .Marianas Synopsis... Satellite imagery shows some showers and thunderstorms within the coastal waters, but most are away from the islands. Wind observations at the airports are reporting a gentle to moderate east-southeast winds, while buoys and altimetry show seas around 4 to 5 feet. && .Discussion... The Tropical Upper Tropospheric Trough (TUTT) and embedded upper-level low is passing to the north of the Marianas this evening and helped to spark isolated thunderstorms across the Marianas, especially just north of Saipan and Tinian. So far most of these thunderstorms have avoided passing directly over the islands, as here on Guam, we have not measured any rain here at the airport and weather office and it has been a similar story for Rota, Tinian and Saipan. Until the TUTT passes far enough to the northwest, the potential for thunderstorms and showers remains elevated tonight. Friday through Saturday night looks to be fairly dry as there nothing to our east that catching our attention to greatly increase the potential for showers or cause a big change in our winds. The next trough or series of trough is expected to move in Sunday night or Monday, but models are not indicating anything major beside some scattered showers through Tuesday, before drying out again. && .Marine... Mainly gentle to occasional moderate trades are expected through the weekend. The southwest to west swell will continue to decrease through the week allowing seas around 4 to 5 feet, to drop to 2 to 4 feet this. The decreasing of swell swill also allow surf to slowly drop along west facing reefs and allow the risk of rip currents to become low along all reefs. The TUTT will keep a moderate risk of lightning through tonight. Shower and thunderstorm chances then drop for Friday through Sunday. && .Eastern Micronesia... The main player in the forecast for eastern Micronesia continues to be the ITCZ (Inter-Tropical Convergence Zone). The ITCZ stretches eastward from near Kosrae to just south of Majuro to across the Date Line. Convection has held off a bit through this afternoon and it appears this will continue into the evening. Therefore, backed off on the timing for increased showers to move into Majuro and Pohnpei. For Kosrae, scattered showers associated with the ITCZ are now moving into the area. With a trade-wind trough moving through the Marshalls, scattered showers and isolated thunderstorms look to move across the atoll later this evening. As the trough continues west, increased showers look to continue across Kosrae Friday as the trough interacts with the ITCZ over the state. The ITCZ should remain active through Saturday. Majuro will see the most activity Friday and Friday night as a couple of stronger troughs move in from east of the Date Line, bringing numerous showers to the atoll. By Saturday, the ITCZ looks to dissipate, though scattered showers remain possible for Kosrae and Pohnpei as the subsequent troughs move through. By Sunday, expect a dry trade-wind pattern to move into the area and continue through at least the middle of next week. Benign marine conditions will continue for the next several days, with mostly light to gentle trade winds, though Kosrae and Majuro could see occasionally moderate winds Friday into the weekend. Combined seas look to remain between 2 and 4 feet. && .Western Micronesia... Satellite observations show isolated showers across Palau, Yap, and Chuuk and much of Micronesia. Combined seas are generally between 2 and 4 feet with the Ngaraard, Babeldaob buoy just under 3 feet. The surface ridge that was over Palau and Yap has slowly progressed westward as a surface trough approaches the region. Scattered showers will be possible along the trough over the next few days as it slowly moves eastward. Seasonal showers are expected towards the latter half of next week behind the trough. Seas will generally remain in the 2 to 4 ft range for Yap and Palau with gentle to moderate winds in place. Seasonal showers are expected for Chuuk through much of the period except for some increased activity Friday and Saturday as the ITCZ pulses up. The marine forecast for Chuuk is similar to Yap and Palau with predominantly 2 to 4 feet seas. Seas may fall to 1 to 3 feet late next week. Winds will remain gentle to moderate across Chuuk State through the period. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Schank Eastern Micronesia: Kleeschulte Western Micronesia: Williams