


Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
576 FXPQ50 PGUM 071908 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 508 AM ChST Tue Jul 8 2025 .Marianas Update... Little change has been made to the forecast. Recent satellite imagery, Doppler radar, and upper air sounding data draw better support for lower PoPs the rest of today and tonight. In addition, increased cloud cover and distance to nearby upper-level features shows lesser support for thunderstorm development, so removed thunderstorms from the forecast through tonight. The marine and surf forecasts remain unchanged. && .Eastern Micronesia Update... An unsettled weather pattern remains across much of the Marshalls and northern Kiribati due to the Intertropical Convergence Zone (ITCZ) and a broad trough at its leading edge. Additionally, this feature is linking up with diffluent upper-level flow to produce deep convection and widespread cloudiness. Meanwhile, patchy clouds and showers are seen to the west, over Pohnpei and Kosrae. As this trough slowly weakens over the course of the day, a fragmented ITCZ pattern will begin to extend farther westward, increasing showers for Pohnpei and Kosrae in the latter half of the week. Only minor changes were made to the forecast today. Numerous showers look to persist near Majuro through the morning, decreasing to scattered in the afternoon. Meanwhile, patchy showers across Kosrae are expected to increase to scattered in the afternoon with the passage of a minor trough. For Pohnpei, saw a slight decrease in precipitable water (PWATs) in the sounding and CIMSS MIMIC TPW, which is supported by little to no surface forcing observed in recent satellite imagery and model trends. As such, lessened shower and thunderstorm potential through tonight. Scatterometry shows light to gentle trades across Pohnpei and Kosrae and variable, gentle to moderate winds near Majuro. Buoy and altimetry data indicate seas are 2 to 4 feet near Pohnpei and Kosrae, and up to 6 feet near Majuro. && .Western Micronesia Update... Satellite imagery shows scattered showers developing across Palau and Yap. This is within a light to gentle westerly flow that eventually converges with a light to gentle trade pattern, generating widespread showers over much of eastern Yap State. Meanwhile, relatively quiet conditions are seen farther east over Chuuk Lagoon. Overall, no major changes were made to the forecast overnight. Yap and Palau will see a gradual increase in showers today, as the pattern shifts to convergent southwesterly flow by tonight. Buoy and altimetry show 1 to 3 foot seas over Palau and Yap, and 3 to 4 feet near Chuuk. && .Prev discussion... /issued 654 PM ChST Mon Jul 7 2025/ Marianas Synopsis... Satellite and radar imagery are showing mostly cloudy skies with scattered showers, mainly over the coastal waters. Local buoys are indicating seas of 2 to 3 feet. Discussion... The Marianas will remain sandwiched between a region of troughing and monsoon flow to the north and west and ridging to the south and east, with moist, converging southerly flow in-between over the islands. Expect generally scattered showers (Probability of Precipitation 30-40 percent) and isolated thunderstorms through the period. An upper-level trough south of the Marianas sliding to the west will bring divergence aloft and keep the shower and thunderstorm potential on the higher end through Tuesday night. Slightly more stable and drier conditions look to build in by midweek as the surface ridge creeps towards the islands, forcing the moist, converging flow off to our northwest. The troughing and moist monsoon flow look to try and build back east towards the Marianas over the weekend, with the shower and thunderstorm potential ticking back up. Throughout the week, if enough clearing allows for sufficient daytime heating and destabilization, we could see island- effect showers and thunderstorms firing off as southerly winds will generally be on the lighter side. Marine/Surf... Light to gentle southwesterlies will slowly pick up and become gentle to moderate on Tuesday, then decrease slightly beginning Wednesday and become light to gentle again by late week. Combined seas of around 3 feet are expected for most of the week, possibly increasing late week or the weekend as a west-northwest swell emanating from a distant tropical disturbance to our northwest arrives. A low risk of rip currents is expected along all reefs for most of the week. Surf and rip risk could rise toward the weekend along west and north facing reefs, as the aforementioned swell arrives to the region. Eastern Micronesia... The ITCZ is producing scattered to numerous showers over Kosrae and RMI. Showers are expected to rebuild into the RMI overnight. A trough east of RMI is what is expected to re-invigorate the showers over the eastern half of the region. The models suggests the ITCZ will flex southward. This will effect southern RMI and eventually Kosrae. Scattered showers are expected to remain in the forecast throughout the period for both RMI and Kosrae. For Pohnpei, a trade-wind convergence zone has set up over the northwestern corner of the region. This will keep scattered showers in the forecast for the next 24 hours or so. Then a brief return to a drier pattern will set up. The ITCZ is expected to arrive in Pohnpei near midweek. This will bring showers back into the high-end scattered showers and the peak of showers is expected Wednesday night into Thursday morning before diminishing back to scattered. Altimetry shows combined seas of 4 to 6 feet. Models suggest a trade-wind swell will gradually build in the east that may bring seas near Majuro up to 6 to 8 feet by the end of the week. Winds are expected to remain light to moderate for much of the week. Majuro is the exception for this as the winds here will build to gentle to fresh by the weekend. Western Micronesia... Winds in Western Micronesia will be light to gentle this week. At Chuuk they will be light to gentle from the east, with combined seas of 3 to 5 feet. Showers should be isolated through Wednesday, then could fill in Wednesday night and remain through Saturday. At Yap, the winds will be light to gentle from west, gradually turning toward the west-southwest which is delaying everyone else. Koror Palau has weather similar to Yap, light to gentle west to southwest winds, isolated showers tonight, then gradually filling in Tuesday for the rest of the week. Marine conditions will be benign other than the chance of thunder. Be on the lookout for lightning, stay below deck for 30 minutes after the latest lightning strike, and you will know you`re safe. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas Update: Montvila East/West Micronesia Update: Cruz Marianas: Stanko East Micronesia: Bowsher West Micronesia: Slagle