FXPQ50 PGUM 210823 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 623 PM ChST Sun Jun 21 2026 .Marianas Synopsis... Visible satellite imagery shows partly cloudy skies and isolated showers for the Marianas. Buoy data supports combined seas of 3 to 4 ft. Invest 94W may bring increasing showers, gusty winds, and thunderstorm potential to the region in a few days. && .Discussion... The Marianas are situated within a col between distant Tropical Storm Mekkhala (07W) and Invest 94W to the east. Scattered showers from this morning have decreased to isolated as the day progressed, and satellite trends support this regime continuing at least through tonight. Due to the light and variable winds forecasted for tomorrow, island-effect showers are the main concern, especially as an upper- level low moves in and Precipitable Water (PWAT) values hover between 1.85 to 2.15 inches according to CIMSS MIMIC trends. Thus, scattered showers and isolated thunderstorms are forecasted for the afternoon hours tomorrow, becoming isolated tomorrow night. Then, conditions will begin to deteriorate as Invest 94W approaches the Marianas. Current model guidance indicates gusty winds, increasing shower potential, and isolated thunderstorms starting as early as Tuesday for Guam and Rota, and Monday night for Saipan and Tinian. Please refer to the Tropical Systems section below for more on Invest 94W. && .Marine... Combined seas will gradually increase by a foot or two as Invest 94W reinforces wind waves and the primary east swell. The southeasterly swell should drop off tonight, quickly being replaced by a southwest swell that is expected to shift more westerly later in the week. There is a moderate risk of rip currents along east- and south-facing reefs, and a low risk of lightning during the afternoon hours of Monday. && .Tropical Systems... Tropical Storm Mekkhala (07W) continues to gradually strengthen, well north-northwest of Koror, with the circulation center located near 16N131E. Maximum sustained winds are 65 mph. Mekkhala will continue to strengthen, possibly becoming a typhoon tonight as it exits Guam's Area of Responsibility. Altimetry shows seas near the center are in the 15 to 18 foot range. Winds and seas will continue to increase as Mekkhala lifts to the west-northwest at around 15 mph. This general course and speed is expected to continue through at least Monday. A weak tropical disturbance, located east of Guam near 13N152E, has been newly dubbed Invest 94W by the Joint Typhoon Warning Center (JTWC). Invest 94W is currently designated as low, meaning it is not expected to develop into a significant tropical cyclone within the next 24 hours, and is being monitored for development. Himawari visible satellite this afternoon depicts a clear low to mid-level circulation with convection developing about the center, mainly to its north and northeast. Models are very split on the development and strength of the disturbance, with general agreement on a northwest track passing near Tinian and Saipan around Tuesday. For now, deterministic and ensemble model guidance show Invest 92W most likely remaining a weak oblong disturbance over the next few days, but some individual models show it developing into a Tropical Depression as it passes the Marianas. For more information on Invest 94W, please refer to bulletins from the Joint Typhoon Warning Center under WMO header ABPW10 PGTW. For information on Tropical Storm Mekkhala, please see bulletins from the JTWC under WMO header WTPN31 and from the National Weather Service under WMO header WTPQ31 PGUM. && .Eastern Micronesia... A Near-Equatorial Trough (NET) remains entrenched across the region, stretching from Guam to just south of Majuro, ending near 5N180. South of this feature, westerly flowcontinues to affect Pohnpei and Kosrae, helping to produce orographic showers over the leeward side of the islands. A subtle surface trough is also seen between Kosrae and Majuro. It's unclear if this trough, which formed today, will maintain integrity over the next few days. With this in mind, we tried to suggest when scattered showers (30 percent potential) versus isolated showers (20 percent potential) may affect both locations. Isolated showers will continue at Majuro during this time as well. Then, as we head towards the weekend, some guidance indicates a more active NET developing with increasing chances of rainfall, especially if the NET settles south slightly or becomes orientated in a more east-west fashion. As for marine conditions, light to gentle winds will prevail with seas of 3 to 5 feet expected. && .Western Micronesia... The convergent southwest monsoon flow has shifted north of Palau and Yap as Tropical Storm Mekkhala continues to move west-northwest and farther away, currently centered near 16.1N 131.9E. Drier conditions prevail this afternoon as a broad surface ridge is setting up far south of the monsoon trough and TS Mekkhala, with just isolated showers expected for Palau this evening. Latest Himawari visible satellite imagery shows scattered showers and isolated thunderstorms developing near and east of Yap, and these are expected to increase across the region through late tonight as convergence increases south of the monsoon trough, bringing shower coverage back up to scattered for Palau after midnight. A slightly drier but generally unsettled pattern will continue for the next few days before the next disturbance starts to push west into the region around midweek, running up against the surface ridge set up in the area. The weak disturbance will maintain a somewhat unsettled pattern through the latter half of the week, as part of a broad monsoon-like trough extending across Micronesia. Farther east, numerous to widespread showers and isolated thunderstorms are seen across eastern Yap State within a broad unsettled convergence zone. Just east of this disturbance, showers remain isolated near Weno, Chuuk this afternoon with weak ridging set up overhead. Model guidance depicts a slight increase in showers overnight with an increase in convergence south of Invest 94W. Overall, the pattern remains messy and unsettled across the region with periods of scattered showers expected into the end of the week as the monsoon-like trough repositions farther south and over the area. Benign sea conditions continue across the region. Latest altimetry and Yap buoy data show combined seas between 3 and 6 feet across the region. Palau and Yap will see a primary southwest swell over the next few days associated with the southwest monsoon pattern, with a secondary north to northeast swell. Chuuk continues to see a primary east to southeast swell with a light secondary swell out of the northeast. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Mesa East Micronesia/Tropical: Doll West Micronesia/Tropical: DeCou