215 FXPQ50 PGUM 301842 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 442 AM ChST Wed Dec 31 2025 .Marianas Update... A shear line near Saipan continues to bring higher shower coverage there compared to Guam and Rota. This is also likely getting a nocturnal boost. Thus, showers should decrease after sunrise. As such, no forecast updates were needed. && .Eastern Micronesia Update... No updates were needed as the forecast remains on track. && .Western Micronesia Update... Shower and thunderstorm coverage has increased at Palau, as a subtle surface trough moves through. As such, we increased the rainfall potential to 50 percent there for today. Otherwise, no forecast updates were needed. && .Prev discussion... /issued 558 PM ChST Tue Dec 30 2025/ Marianas Synopsis... There are two advisories/statements in effect for the Marianas. They are High Surf Advisory (HSA) and High risk of Rip Currents statement (HRRC). Both the advisory and the statement are for north facing reefs. Satellite imagery shows partly cloudy skies, while radar imagery shows a few isolated showers over the region. Altimetry shows combined seas of 7 to 9 feet to the west of the Marianas, and buoy data shows 6 to 8 foot swells at 11 seconds. Discussion... A shear line fragment is continuing to gradually moving through the region. This fragment has moved a little slower than anticipated, and gradually moving southward through the Saipan's coastal waters. Winds near Tinian and Saipan will continue to be around 15 to 20 mph through around Wednesday before gradually diminish to around 10 to 15 mph. Showers associated with this fragment are expect to begin to build in for Tinian and Saipan after midnight tonight as the shear line moves southward. Then, a return to a drier trade-wind pattern is expected for Tinian and Saipan once this shear line fragments passes. Models suggest that this fragment may to pass through Rota and Guam around Wednesday night bringing with it low-end scattered showers. Otherwise, these islands can expect to see a drier trade-wind pattern through the weekend. Marine/Surf... Seas of 7 to 9 feet will continue while the shear line is passing over the region, then seas are expected to gradually diminish, falling to around 5 to 7 feet later this week. Gentle to moderate trade winds for Guam and Rota, and moderate to fresh for Tinian and Saipan through Wednesday. Winds near Tinian and Saipan are expected to diminish to gentle to moderate for the latter half of the week. Pulses of the north swell are continuing through the region. These pulses have maintained surf of 8 to 10 feet. Model trends suggest a downward trend in the swells and surf, however, buoy data and local observers suggest that trend has not yet started. Once these pulses pass, the surf is expected to gradually diminish. Eastern Micronesia... Partly cloudy skies with isolated showers are present at all three forecast points, with scattered showers and isolated thunderstorms to the east of Kosrae. Altimetry shows seas of 5 to 7 feet across the region. Pohnpei buoy shows seas of around 7 feet and Kosrae buoy has seas between 4 and 5 feet. The Inter-Tropical Convergence Zone (ITCZ) remains the primary player across eastern Micronesia. Just south of the ITCZ, south of Kosrae, a weak circulation has developed that is helping to increase convergence along the ITCZ near Kosrae. Although showers have decreased to isolated for now, scattered showers and isolated thunderstorms seen to the east of the island are expected to move back into the area through the evening. The ITCZ is expected to remain active through Wednesday night, when it should drift south and weaken. This will allow for a dry trade-wind pattern to move into the area and continue through the weekend. For Pohnpei and Majuro, a dry trade-wind pattern is expected to continue through the weekend as the ITCZ remains south of both locations. Altimetry shows seas between 5 and 7 feet across the region. Kosrae and Pohnpei buoys agree, with Pohnpei showing seas around 7 feet and Kosrae between 4 and 5 feet. The trade swell height and period have subsided sufficiently to allow the surf to fall below hazardous levels of 8 feet along east facing reefs of Kosrae. Trade swell looks to build back into the region later in the week, and could bring another round of hazardous surf to Kosrae's east facing reefs Thursday night or Friday. Otherwise, seas will be choppy due to moderate to fresh trade winds and wind waves, trade swell and a small north swell, but seas are not expected to be hazardous to small craft operations. Western Micronesia... A drier weather pattern is spreading across Chuuk State as the series of trade-wind troughs continue to shift westward through the region. Chuuk is expected to remain in this drier pattern through at least the weekend, with winds becoming moderate to fresh Wednesday through Friday as the trade winds strengthen slightly. The bulk of the convection associated with the troughs is still east of Palau and well south to southwest of Yap Proper this evening, as scattered showers and isolated thunderstorms fluctuate in coverage and intensity along the series of troughs. Based on current model trends, the best potential for showers and thunderstorms at Palau will be during the daytime hours of Wednesday and Thursday (40 percent chance of showers), with chance of showers then mainly oscillating between 20 to 30 percent over the next severals days as trade-wind troughs pass through the region. Most of these showers will pass south of Yap Proper, though scattered showers may lift into Yap Wednesday night, Yap should remain in a fairly dry trade-wind pattern into the weekend. Altimetry data and the drifting buoy east of Yap suggest seas are between 5 and 7 feet this evening. An increase in the trade swell, along with the lingering north swell, will boost seas and surf at Chuuk slightly around Thursday night or Friday, but at this time seas are expected to remain below 10 feet and surf is not expected to reach hazardous levels of 9 feet along north facing reefs and 12 feet along east facing reefs. Later, a pulse north to northwest swell will impact Palau and Yap this weekend or early next week, potentially causing surf to reach hazardous levels of 9 feet along north and west facing reefs. Light to moderate winds will persist at Yap and Palau over the next several days. Moderate trades near Chuuk are expected to increase to moderate to fresh Wednesday and remain near this level through Friday. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...High Rip Current Risk until 4 PM ChST this afternoon for GUZ001. High Surf Advisory until 4 PM ChST this afternoon for GUZ001. MP...High Rip Current Risk until 4 PM ChST this afternoon for MPZ001>003. High Surf Advisory until 4 PM ChST this afternoon for MPZ001>003. Marianas Waters...None. && $$ Marianas/East and West Micronesia Update: Doll Marianas: Bowsher East Micronesia: Kleeschulte West Micronesia: Schank