Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
051 FXPQ50 PGUM 041954 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 554 AM ChST Sat Sep 5 2026 .Marianas Update... There was a cluster of thunderstorm activity near Tinian and Saipan this morning, which could be what the models were trying to hint at for today. So they may have been pretty close, it`s just that it`s already in the past. So now, satellite and radar show partly sunny skies and isolated showers over the Marianas, but we could get more scattered showers moving in later, so not too many changes to the Marianas forecast. && .Marine... An Altimetry pass west of the Marianas shows that the swells have certainly not grown, and the wave model data indicates they should now be starting to shrink. The model winds show that the main fetch has turned away from us, so this is all fitting together, so went ahead and allowed the high risk of rip currents and high surf advisory to expire as scheduled. The west to northwest swell is forecast to continue to diminish slowly, allowing combined seas to fall from 5 to 7 feet today to between 3 and 5 feet by next Tuesday. && .Tropical Systems... Invest Area 97W was warned on overnight, so it is now officially Tropical Storm 23W. At 100 AM, it was located near 23.1N and 137.6E, which is about 815 miles northwest of Guam. It had maximum sustained winds of 45 mph and was moving north at 21 mph. It is expected to turn to the northwest with a decrease in forward speed. It is forecast to remain over open ocean, and could start weakening Sunday, and might even dissipate Tuesday. For more information on Tropical Storm 23W, please refer to the Tropical Cyclone Warnings from the Joint Typhoon Warning Center under WMO header WTPN32 PGTW and the Tropical Cyclone Public Advisories from the National Weather Service under WMO header WTPQ32 PGUM. && .Eastern Micronesia Update... Eastern Micronesia has that convergence boundary that has been pushing across. No significant changes were needed at Majuro. Kosrae I changed the weather from isolated to scattered/isolated, and at Pohnpei I changed the weather from scattered to numerous/scattered. Collect that water, you might be needing it soon. && .Western Micronesia Update... Has the expected El Nino drought started early? Hopefully not, Palau and Yap would appreciate one last chance to collect some water resources, I`m sure. The forecast is not overly encouraging though, with Palau expected to have 5 days of only isolated showers, Yap has 4 days then maybe 1 day of barely scattered. Chuuk looks a little better on the surface, but when I dug deeper by looking through their observations, it looks like they received no rain yesterday. Chuuk has plenty of clouds, but is anything falling from them, that is the question. No significant changes were needed at Palau and Yap. Reduced shower coverage at Chuuk from scattered showers and isolated thunderstorms to just isolated showers for today. && .Prev discussion... /issued 547 PM ChST Fri Sep 4 2026/ Marianas Synopsis... Radar and satellite imagery depicts high-end scattered showers and isolated thunderstorms across the Marianas. Combined seas are around 6 to 8 ft. The High Surf Advisory and High Risk of Rip Currents along west-facing reefs remains in effect through late tonight with conditions expected to improve shortly thereafter. Discussion... An active weather pattern will persist across the Marianas beginning this evening through Saturday night before tapering down on Labor Day. A surface trough associated with Invest 97W to the west and a col to the east places the region within an unsettled convergence zone. As seen on satellite, westerly flow is buckling against the frontmost quadrants of the col, and as the col continues moving west- northwest, numerous showers and isolated thunderstorms with possible locally heavy showers are expected Saturday and Saturday night, potentially heavier over Saipan and Tinian. Scatterometry depicts moderate to fresh southwesterlies which will taper down to gentle to moderate after tonight, with occasional convective gusts up to 25 mph possible. Scattered showers and isolated thunderstorms are forecasted through Labor Day, followed by a potential dry spell through the remainder of next week. Marine... Model guidance suggests the elevated westerly swell to linger slightly longer than previously anticipated, so surf along west- facing reefs will remain 7 to 9 ft through tonight. As such, there is a high risk of rip currents, so both hazards were extended until 4 AM ChST Saturday. Surf is expected to drop below hazardous levels by this time, but this will continue to be monitored overnight. Combined seas are 6 to 8 ft and will drop by a foot or two through the next week. Tropical Systems... Invest 97W is located about 370 miles south-southwest of Iwo To near 19.2N 138.3E and is moving northwest. The Joint Typhoon Warning Center (JTWC) has upgraded 97W to high, and has issued a Tropical Cyclone Formation Alert (TCFA). This means that development into a significant tropical cyclone (tropical depression) is likely within the next 24 hours. Invest 97W is now showing a tightly closed Low- Level Circulation Center (LLCC). 97W is expected to move northwest over the next few days as it continues to consolidate. Invest 97W will have no direct impact on Micronesia nor the Marianas. For more information on Invest 97W, see bulletins issued by JTWC under WMO headers WTPN21 PGTW and ABPW10 PGTW. Eastern Micronesia... A band of convergence to the southwest of the monsoon trough is generating scattered showers and isolated thunderstorms across Pohnpei and Kosrae this evening. This area of convection looks to slowly move away from Kosrae through the night, with isolated showers expected over the island by midnight. Convection will linger at Pohnpei a bit longer as the monsoon trough slowly drifts west, pushing the band of convergence toward Chuuk. A dry pattern will then dominate at both Pohnpei and Kosrae into the beginning of next week. The dry pattern at Majuro looks to continue through the weekend. Early next week, the monsoon pattern looks to become a bit more active, with a weak surge developing, bringing increased showers and thunderstorms to Majuro Monday, with the convection increasing westward toward Kosrae and Pohnpei by Tuesday. Light to gentle winds will prevail through the weekend and into the beginning of next week. Then a weak monsoon surge will bring gentle to moderate winds to Majuro and Pohnpei, with moderate to fresh winds at Kosrae. Seas will become a bit choppy, with a chaotic wave pattern over the region. Seas will remain fairly low, however, peaking at around 5 to 6 feet near the middle of next week. Western Micronesia... Overall, the region remain south and west of the monsoon trough, that stretches across the far northern Marianas and curves southeastward into eastern Micronesia. Fairly dry conditions persists across Yap and Palau through early next week. Showers are building across northeastern Chuuk State, tied to the increase in northwesterly convergence towards the monsoon trough and disturbance in eastern Micronesia. This band of convergence gradually shifts westward in the coming days, producing scattered showers and isolated thunderstorms across Chuuk through the weekend, then shower coverage slightly lowers to isolated to scattered Monday and Tuesday as the feature moves farther westward, bringing scattered showers to Yap around Wednesday. Southwesterly convergence alongside the monsoon trough begins to set up across Chuuk around Wednesday as well, bringing another increase in scattered showers and isolated thunderstorms towards the latter half of next week. Latest altimetry data shows combined seas of 3 to 5 feet near Palau and 4 to 6 feet across Yap and Chuuk coastal waters. Combined seas are expected to subside another foot as westerly swells diminish slightly. Light to gentle winds persists over the next several days with an increase in gentle to moderate southwesterly winds at Chuuk towards the latter half of next week. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas/East and West Micronesia/Tropical Update: Stanko Marianas: Mesa East Micronesia/Tropical: Kleeschulte West Micronesia: Cruz