textproduct: Tiyan

Marianas Synopsis

Radar and visible satellite imagery show isolated, light trade-wind showers, with highest coverage around Guam and Rota. Models and observations show combined seas of 5 to 6 feet.

Discussion

Showers are expected to remain largely isolated through Friday. Occasional patches of weak, scattered trade-wind showers will be possible, particularly in the late night hours over the coastal waters. Gentle winds tonight will become gentle to moderate Wednesday and hold steady before possibly decreasing with the arrival of a trough Friday night. Models indicate this trough will move into or just north of the Marianas by Friday. So the location remains uncertain, however, confidence is high enough to put scattered showers in the forecast for Tinian and Saipan, and isolated thunderstorms for all islands. By Saturday night, the isolated trade- wind shower regime will likely return.

Marine

Gentle to moderate winds are expected through Friday. Combined seas of 5 to 6 ft will now remain steady, before possibly increasing slightly in the latter half of the week due to an increasing trade- wind swell. There is a moderate risk of rip currents along north, east, and west-facing reefs. Swells consist of a diminishing northwest swell from distant Typhoon In-fa and an east-northeast trade-wind swell. Scattered showers will be possible after midnight tonight and Wednesday night. A trough may move into the Marianas Friday night and Saturday, possibly bringing more scattered showers and isolated thunderstorms. Therefore, a moderate risk of lightning is possible Friday night and Saturday.

Tropical Systems

Typhoon In-fa continues to churn across the open Pacific while retaining its symmetry on visible imager. The 1 PM ChST position has In-fa at 23.2N 139.1E, located 175 miles southwest of Iwo To, moving west (280 degrees) at 7 mph. However, the latest visible imagery suggests it may have made that northward turn. Typhoon force winds extend outward from the center up to 35 miles, mainly on the northern side. Tropical storm force winds extend outward from the center up to 115 miles.

For more information please refer to bulletins from the Joint Typhoon Warning Center under WMO header WTPN31 PGTW and from the National Weather Service under WMO header WTPQ31 PGUM.

Eastern Micronesia

The main forecast challenge continues to be rainfall potential, mainly at Kosrae. Currently, the monsoon trough is in an east-west orientation near 4N, which is a little further south than yesterday. This is far enough south to only produce isolated showers for most of the time across Pohnpei, Kosrae, and Majuro. Although, if it ends up lifting slightly north, rainfall coverage could increase some for Kosrae. Looking ahead, the trough looks to weaken, which in turn weakens surface convergence, reinforcing the isolated shower approach.

For our mariners, look seas of 4 to 6 feet to continue, possibly dropping a foot later in the week. Winds will be light to gentle area-wide.

Western Micronesia

A monsoon-like, near-equatorial trough remains stretched out across the region, producing patchy showers across Palau and Chuuk. Active weather continues on the southern side of the trough, across open waters south of Yap State and western Chuuk State. Drier air lingers across Yap, so fair weather is expected to persist through the week. For Palau and Chuuk, overall weather pattern remains fairly quiet and mainly isolated showers are expected through Saturday, then a slight uptick in showers is possible Sunday due to an increase in trade-wind convergence.

Combined seas are 4 to 6 feet, with seas increasing to 5 to 7 ft at Yap and Palau from north to northeast swell emanating from distant Typhoon In-fa. Hazardous surf of 7 to 9 feet continue along north- facing reefs of Yap and Palau and a High Surf Advisory remains in effect through late tonight, although elevated surf may still persist through Wednesday as the pulse of long-period swell diminishes. Benign seas and surf continue at Chuuk, comprised of a dominant northeast swell and diminishing northwest swell. Combined seas of 3 to 5 feet peak up to 6 feet around Thursday night from a brief increase in northeast swell.

GUM WATCHES/WARNINGS/ADVISORIES

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