Area Forecast Discussion

Marianas Synopsis

Partly cloudy skies and isolated to scattered island-effect showers are occurring over Guam and adjacent southern coastal waters. Mostly clear skies are apparent elsewhere in the region. Altimetry indicates combined seas of 5 to 7 FT.

Discussion

Another round of little to no rainfall is expected tonight, especially for the CNMI, as the current wedge of drier air lifts north. Then, Precipitable Water (PWAT) values of at least 2.0 inches paired with light and variable winds will move over the region, so scattered island-effect showers in the afternoon are expected for Guam over the next couple of days. Next week, light to gentle trade winds will return to the region, so afternoon island-effect showers will be concentrated over the western shorelines and adjacent coastal waters for Guam. Shower coverage will remain isolated for the CNMI throughout the forecast period.

Marine

Combined seas are 5 to 7 FT and will remain as such through the forecast period. Model guidance shows another pulse in the long- period northwesterly swell emanating from Typhoon In-fa around Sunday night and Monday, which would lead to advisory-level surf. Therefore, the High Surf Advisory and High Rip Current Risk Statement were extended regardless of an expected dip in surf heights on Sunday. Surf observations today indicated surf of 7 to 9 FT along north and west facing reefs, so reflected those values in the forecast for tonight and Sunday night. In addition, a secondary trade swell will build across the region next week, eventually becoming the dominant swell as In-fa and its respective swells continue moving away to the north.

Tropical Systems

Typhoon In-fa is located around 21.4N 142.9E. As of 1:00 PM ChST, In-fa was moving north-northwest at 13 MPH. Maximum sustained winds are 130 MPH, making In-fa a low-end Category 4 typhoon. According to the Joint Typhoon Warning Center (JTWC) track, In-fa is forecast to slowly stall and make a small clockwise loop before resuming its general motion towards the northern Pacific next week. Visible satellite imagery continues to show a well-defined eye with a near- symmetrical storm structure. Regardless, In-fa is forecast to continue weakening over the next few days, possibly becoming a Category 2 typhoon around Monday.

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 monsoon trough looks to settle south over the next few days, likely stalling along a Pohnpei to Majuro line (or just south of there). This limits surface convergence at both of those locations after tonight, with just isolated showers expected most of the forecast period. Farther south at Kosrae, with the trough just north of you, you can expect to see scattered showers most of the forecast this forecast period, with the exception being tonight when just isolated showers are expected.

For our mariners, look for light to gentle winds prevailing through the forecast period, with seas of 4 to 6 feet expected.

Western Micronesia

The monsoon trough borders the region, passing along 10N near northern Yap State, before curving towards Typhoon In-fa to the distant north. The next segment of the monsoon trough bends southeastward to pass through Pohnpei State. The monsoon trough looks to shift southward slightly, but convection is disorganized overall. Isolated to scattered showers are expected over through much of the upcoming week for Yap and Palau. The segment of the trough moving towards Chuuk is expected to bring a period of scattered showers Sunday and Sunday night, with an area of showers persisting across southern Chuuk State on Monday and early Tuesday morning, along increased convergence on the southern side of the monsoon trough.

Latest altimetry data shows combined seas of 3 to 5 feet, with seas increasing to 6 ft north of Yap and Palau from a pulse of northeast swell from Typhoon In-fa. Seas will continue to build to 4 to 6 feet across Yap and Palau, possibly reaching 7 feet at Yap early next week. Additionally, the long-period swell will also support elevated surf along north-facing reefs over the next few days, with seas possibly exceeding hazardous levels of 9 feet along north-facing reefs of Yap around Monday night or Tuesday. Meanwhile, benign seas and surf continue at Chuuk, with a slight increase in northeast swell increasing seas to 4 to 6 feet around Tuesday.

GUM WATCHES / WARNINGS / ADVISORIES

GU...High Rip Current Risk through late Sunday night for GUZ001.

High Surf Advisory until 4 AM ChST Monday for GUZ001.

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

High Surf Advisory until 4 AM ChST Monday for MPZ001>003.

Marianas Waters...None.