textproduct: Tiyan

Marianas Synopsis

Skies are mostly cloudy with isolated showers over Guam and Rota this afternoon as the remnants of a weak outflow boundary sweep the islands. Mostly clear conditions are seen to the north over Tinian and Saipan. There is an area of scattered showers east of the Marianas associated with a region of localized surface convergence and shallow troughing. A broad area of showers and cloudiness is seen within the decaying remnants of a shear line over the far northern Marianas. Surface observations show fresh east-northeast winds with frequent gusts in the mid to upper 20s.

Discussion

Satellite trends show diminishing showers upstream of the Marianas as a mostly dry pattern continues. An area of showers associated with shallow troughing east of Guam looks to pass largely south of the Marianas overnight, but may bring slightly increased coverage for Guam and Rota. However, coverage is expected to remain isolated through the weekend into early next week, according to ensemble model guidance. Moderate to fresh winds will diminish for the weekend before a modest trade wind surge builds in early next week.

Marine/Surf

The latest buoy and altimetry data show combined seas of 7 to 10 feet, with combined seas of 10 to 13 feet across the far northern Marianas as a larger northwesterly swell moves in. Winds will be moderate to fresh for the remainder of the week, decreasing slightly this weekend. Gusts of 25 to 30 knots will be frequent tonight through Friday as the remnants of a shear line dip slightly further south toward the Marianas. There is a high risk of rip currents for west, north, and east facing reefs, but the rip risk should diminish for west facing reefs tonight as the northwesterly swell becomes more northerly. The high risk for rip currents for east facing reefs may persist into the weekend.

Eastern Micronesia

Mainly scattered showers and isolated thunderstorms today will increase as the Inter Tropical Convergence Zone (ITCZ) becomes better organized and creeps north, with multiple trade troughs passing through the ITCZ. Expect showers to become numerous to, at times, widespread and locally heavy for Kosrae tonight, and for Pohnpei and Majuro tomorrow. Rainfall amounts of 4 to 8 inches are forecast through Sunday for Kosrae and Pohnpei, with up to 10 inches possible in spots. This could lead to a slight potential for localized flash flooding and landslides. Gusty winds will also be possible. Showers diminish at Majuro this weekend and at Kosrae and Pohnpei early next week as the trade flow increases and the ITCZ fragments and shifts south and west. However, look for shower and thunderstorm potential to tick back up as next week progresses and the ITCZ becomes better developed and drifts back north.

Elevated trade swell and elevated northerly swell emanating from strong mid-latitude storm systems, along with fresh to strong trade winds, will lead to combined seas of 8 to 11 feet. A Small Craft Advisory is out for Kosrae through tomorrow, for Pohnpei through tomorrow night, and for Majuro through Saturday. The Small Craft Advisories may need to be extended as the elevated seas and winds will likely continue through the weekend. The trade flow looks to subside next week as the pressure gradient relaxes, with seas and winds diminishing.

Western Micronesia

Broad, unsettled weather is in store for much of western Micronesia. A convergence zone has comfortably situated over Palau, bringing numerous showers and some thunderstorms through Friday, followed by a period of various disturbances moving across for much of next week. On-and-off showers are expected at Yap for much of the forecast period, as a wetter weekend is followed by a diminishing trend to much more pleasant weather in the second half of next week. Chuuk, on the other hand, will see patchy showers become increasingly more intense as a much more active trade-wind surge makes its way across Saturday and Saturday night.

Combined seas of 6 to 8 feet at Palau are expected to diminish a foot or two in the next few days, staying as such for the rest of next week. Combined seas of 7 to 10 feet near Yap are expected to diminish overnight, becoming no longer hazardous to small craft thereafter. Meanwhile at Chuuk, 8 to 11 foot seas have developed, producing sea conditions hazardous to small craft; as such, a Small Craft Advisory is valid through Friday afternoon. Hazardous surf generated by elevated north swell and incoming north swell is expected to persist through early Friday morning at Yap, and is now producing said hazardous surf along north facing reefs of Chuuk through Friday afternoon. As such, a High Surf Advisory is not only valid for Yap through Friday morning, but also for Chuuk through Friday afternoon. There is a chance for Chuuk's Advisory to be extended, if conditions warrant.

GUM WATCHES/WARNINGS/ADVISORIES

GU...High Rip Current Risk through Friday afternoon for GUZ001.

High Surf Advisory until 4 PM ChST Friday for GUZ001.

MP...High Rip Current Risk through Friday afternoon for MPZ001>003.

High Surf Advisory until 4 PM ChST Friday for MPZ001>003.

Marianas Waters...Small Craft Advisory until 5 PM ChST Friday for PMZ151>154.