Area Forecast Discussion

Marianas Synopsis

Light to gentle southerlies prevail across the Marianas. Satellite imagery and Doppler radar indicate flattening of the light island showers over Guam and Saipan. Tanapag buoy shows seas are just below 9 feet.

Discussion

A ridge has settled over the Marianas as TS Sinlaku (04W) exited NWS Guam's Area of Responsibility (AOR) to the north-northeast past Minamitorishima, allowing light island showers to former along the axis of Guam and Saipan. While showers will remain minimal overnight as mostly clear skies develop, there is a chance for the light haze observed the last few days to continue into the night. Little to no showers and cloud cover the next few days may exacerbate the heat across the Marianas as power outages continue to plaque most residents as recovery efforts continue post-Sinlaku. Hydration and decreased daytime exposure to the sun will help alleviate heat exhaustion risks, especially for the more vulnerable populations. A gentle to moderate trade-wind pattern is expected to return sometime in the second half of the week as a second high-pressure ridge moves in following a disintegrating Sinlaku well north of Wake Island.

Marine

Combined seas of 7 to 9 feet are expected to decrease by several feet over the next several days as various distant swells weaken considerably. As such, seas are no longer expected to be hazardous to small craft beginning tonight, so a Small Craft Advisory was allowed to be expired. Even so, seas will remain choppy overnight as weaker pulses from distant Sinlaku continue to make their way across the region. As Sinlaku continues to move away to the north-northeast, the primary swell has shifted to the north and decreased, allowing surf to fall below hazardous levels along west and south facing reefs while remaining hazardous along north facing reefs overnight. As such, surf is expected to remain below hazardous levels along south and west facing reefs beginning tonight, as well as the rip current risk dropping to moderate along said reefs. Hazardous surf and a high rip current risk will remain along north facing reefs of the Marianas overnight. Surf is likely to further decrease along all reefs the next several days, allowing the rip current risk to drop further along all reefs and surf to drop below hazardous levels along north facing reefs Monday.

Eastern Micronesia

A trade-wind trough is currently interacting with the fragmented ITCZ across portions of eastern Micronesia this afternoon. Numerous showers and isolated thunderstorms are observed centered roughly around Kosrae and this will continue through the evening hours. Conditions should improve to scattered showers after midnight as the trade-wind trough propagates westward and weakens. Though, the isolated thunderstorm threat will persist overnight. Scattered showers, along with isolated thunderstorms, can be expected at Pohnpei overnight as the weakening trough approaches. Another trade- wind trough east of the Marshall Islands will bring scattered showers and isolated thunderstorms to eastern Micronesia over the next couple of days as it propagates westward and interacts with the weakening ITCZ fragments, first at Majuro, then Kosrae, and potentially Pohnpei. Mostly scattered showers and isolated thunderstorms will persist at all the forecast sites through early this week with a few periods of only isolated showers possible. Mostly gentle to moderate east to southeast winds will continue at all three forecast sites through most of Monday, with a brief period of light to gentle south to southwest winds Monday night and Tuesday. Light to gentle east to northeast winds are expected to develop starting late on Tuesday and will increase late this week.

Combined seas of 4 to 6 feet will continue to diminish this week, eventually dropping another foot or so by midweek. Seas are expected to increase late this week as a northeast swell builds into the region.

Western Micronesia

A very quiet pattern persists across the region, with satellite imagery depicting mostly clear conditions across much of western Micronesia this afternoon. Despite fairly low PWATs, brief island- effect showers developed over the major islands of Palau and over Yap Proper earlier in the day, with this morning's scatterometry indicating a very light wind field across the entire region. Chuuk remains in a quiet ridging environment between weak troughs centered just west of Pohnpei and southeast of the Marianas.

Latest model guidance indicates heavy showers developing east of Chuuk late tonight as convergence increases along the approaching trough on the far western periphery of the ITCZ, located just east of the coastal waters. The ITCZ, or ITCZ fragments, look to gradually push west into Chuuk State over the next few days as individual embedded troughs wax and wane, maintaining at least scattered showers and isolated thunderstorms for much of the coming week. These features will lead to increasing shower and thunderstorm chances toward the end of the week for Yap and Palau as well. In the meantime, a very dry, quiet pattern will continue across far western Micronesia. Tomorrow afternoon presents another opportunity for island-effect showers over Yap and Palau with the continuation of very light winds, despite overall limited atmospheric moisture.

North-northeast swell from distant Tropical Storm Sinlaku continues to move across Yap and Palau, bringing elevated surf along north and east facing reefs over the next few days. The High Surf Advisory and a Coastal Flood Statement was extended for north facing reefs of Yap through late Monday night. Hazardous surf of 8 to 11 feet, combined with the higher high tides with the new moon cycle, may produce minor coastal inundation along northern shorelines at times of high tide. Combined seas of 6 to 8 feet gradually subside to 3 to 5 feet towards the middle of next week as north to northeast swells subside.

GUM WATCHES / WARNINGS / ADVISORIES

GU...High Rip Current Risk through late tonight for GUZ001.

High Surf Advisory until 5 AM ChST Monday for GUZ001.

MP...High Rip Current Risk through late tonight for MPZ001>003.

High Surf Advisory until 5 AM ChST Monday for MPZ001>003.

Marianas Waters...None.