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Marianas Update

The forecast remains generally on track for the Marianas. Did decrease showers down to isolated today based off radar/satellite trend and drier air pushing in from the east which evident on the CIMMS MIMIC Layer PWAT imagery. Showers look to become scattered again tonight as a subtle trade trough looks pushes into the region. A TUTT cell west of Wake Island and a monsoon trough in western Micronesia are slowly moving towards the Marianas and will be increasing the potential for showers and thunderstorms over the next few days.

Gentle to moderate southeast winds will continue across the region for most of the week, with seas of 4 to 6 feet building to 5 to 7 feet by Thursday as the west-southwest swell builds. There will be a moderate risk of rip currents along east facing reefs of the Marianas through at least Wednesday. There will be a moderate risk of rip currents along east facing reefs of the Marianas through at least Wednesday. Around Wednesday night or Thursday, a moderate risk looks to begin along south and west facing reefs as the west-southwest swell builds.

Eastern Micronesia Update

Little change at Pohnpei as the trough near Kosrae gradually approaches. As clouds have diminished, went ahead and lowered PoP's from 40 to 30, although both are scattered. With Kosrae still being near the middle of the activity, increased the PoP's there a bit today, although both 30 and 40 are scattered. Tonight's forecast saw basically no change. And with Majuro being along the north edge of the showers in the Marshalls, also raised the PoP's there just a bit, to around the halfway point, at 50% scattered.

Majuro Waters will be around 10 to 15 knots, with seas of 4 to 6 feet. Kosrae Waters will have winds of 5 to 10 knots, and seas of 3 to 5 feet. Pohnpei Waters will be 10 to 15 knots for winds today, becoming 5 to 10 knots afterward, with seas of 4 to 6 feet becoming 3 to 5 feet Wednesday night.

Western Micronesia Update

Added headlines to Palau and Yap for gusty and showery monsoon weather the next day or two. Added gusts up to 25 knots for the next 4 periods at Palau and the next 3 at Yap. Increased the PoP's to widespread today and maintained numerous tonight at both Yap and Palau. A gap has opened in the showers near Chuuk, so took a numerous forecast, and lowered it to a low-end scattered forecast.

Chuuk Waters will have winds starting at 10 to 15 knots, gradually becoming 5 to 10 knots. Seas will be 4 to 6 feet at first, then decline to between 3 and 5 feet. Yap Waters will have 10 to 15 knot winds with gusts to 25 knots, becoming 5 to 10 knots by Thursday. Palau Waters will have similar gusts today, then winds of 10 to 15 knots most of the week. Seas will start at 5 to 7 feet, then could diminish to between 3 and 5 feet by Saturday.

Prev discussion

/issued 510 PM ChST Mon Jul 14 2025/

Marianas Synopsis... Satellite imagery shows mostly cloudy skies across the Marianas, with isolated showers near the islands. Scattered showers are starting to develop to the west and south of Guam, along convergent flow north of the monsoon pattern across western Micronesia. Seas are around 4 to 5 feet, driven by the primary trade swell, a weak secondary westerly swell, and gentle to moderate east to southeast winds.

Discussion... So far showers have been fairly isolated across the Marianas, but as the previous forecast mentioned, convergent flow is increasing near the Marianas, mainly west and south of Guam this evening. This has lead to an increase of showers over the past few hours southwest of Guam, and this area of convergence is starting to lift northward, which should cause scattered showers to move into the Marianas tonight and potentially into Tuesday as a trade-wind trough east of the Marianas will likely move near the Marianas Tuesday. Still not expecting any thunderstorms to develop tonight or Tuesday, but the TUTT cell west of Wake Island continues to slowly drift westward and is still expected to reach the Marianas around Wednesday or Thursday, increasing the potential for thunderstorms. Model guidance also continues to move the monsoonal pattern across western Micronesia closer to the Marianas late this week which will also promote a wet pattern for the Marianas. Since yesterday, the GFS has trended slightly towards the ECMWF, which pulls the monsoon trough slightly more northwest, suggesting showers will be more scattered and episodic in nature, but there is still some uncertainty in the actual develop of the monsoon trough and overall pattern, so exact details such as timing of these showers and what days may see the most rain will be difficult to pinpoint for later this week and into early next week.

Marine... Expect scattered showers to develop across the coastal waters overnight as convergent flow southwest of Guam shifts northward. Gentle to moderate east to southeast winds will continue across the region for most of the week, with seas of 4 to 6 feet building to 5 to 7 feet by Thursday as the west-southwest swell builds. A TUTT cell near Wake Island and a monsoon trough in western Micronesia are slowly moving towards the Marianas and will be increasing the potential for showers and thunderstorms starting as early as Wednesday.

Eastern Micronesia... Scattered showers are seen across Pohnpei, Kosrae, and Majuro with numerous showers seen across and south of Kwajalein and south of Pohnpei. Buoy and altimetry data across eastern Micronesia shows combined seas generally between 5 to 7 feet with a few isolated 8 foot seas apparent on altimetry data.

Conditions across eastern Micronesia have quieted some as the widespread showers over Pohnpei have stratified out. Scattered showers are present across much of the region. Shower coverage looks to stay low to medium (30 to 40%) scattered through tomorrow for Majuro and through Thursday for Kosrae and Pohnpei. Towards the end of the week, convection is forecast to increase across the region as trade-wind convergence increases and the ITCZ pulses back up.

Combined seas are generally between 5 and 7 feet, but altimetry has picked up on some localized 8 foot seas, especially across the RMI. The Small Craft Advisory has been cancelled for Pohnpei. The latest scatterometer data shows winds have fallen below 22 knots with pockets of 15 to 20 knot winds remaining. Choppy seas will remain possible where heavier showers occur. Combined seas are forecast to fall the next few days with seas falling to 3 to 5 feet later this week.

Western Micronesia... Not much changed in the reasoning behind the forecast for western Micronesia. For Yap and Palau, The monsoon trough remains the main player in the forecast. For tonight, a band of numerous showers and isolated thunderstorms is in place across Palau and looks to remain over the Republic through the night. Monsoon flow is spreading this convection northeast toward Yap Proper. Therefore will maintain numerous showers and isolated thunderstorms across Palau for tonight, with isolated showers increasing to high-end scattered showers and isolated thunderstorms for Yap. For the next few days, everything depends on what actually occurs over the region. The latest model run shows all models still in agreement that a circulation will develop over the Philippine Sea north of Yap and palau. What remains questionable is the strength and actual location of the disturbance. The GFS remains the most aggressive, though it has come more in line with the other models. The GFS also keeps the circulation farther east, while the Canadian, ECMWF and NBM are all farther west. Since most of the models are now showing a monsoon surge into Yap and Palau as this disturbance develops, decided to increase shower coverage to numerous at Palau Tuesday night and Wednesday for Yap, with the mention of gusts and possible locally heavy showers. Current guidance does keep the heavier rainfall amounts north of both Yap Proper and Palau at this time. Regardless of the development of the circulation, the expected surge and continued monsoon pattern looks to maintain a wet pattern across Palau and Yap for the next several days.

For Chuuk, numerous showers are seen to the east, pushing toward Weno. Expect these showers to move into Weno later this evening. Mostly just showers are evident with the trough, though instability remains high enough to add isolated thunderstorms to the mix. As this trough approaches, it will pull the western end of an ITCZ into the area. There is also a weak Near-Equatorial Trough (NET) seen to the south of Weno. These features will interact to maintain numerous showers across Chuuk through Tuesday afternoon. Afterward, the NET and ITCZ look to slowly weaken across Weno, allowing showers to decrease a bit, though POPs look to remain in the 30 to 50 percent range into the weekend.

No changes were made to the marine forecast. Seas will be a bit rough at times with the strong gusts associated with the showers and thunderstorms over all three locations.

GUM WATCHES/WARNINGS/ADVISORIES

GU...None. MP...None. Marianas Waters...None.