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Marianas Synopsis

Satellite imagery shows partly cloudy skies, while radar shows a few isolated showers over the region. Altimetry shows 2 to 3 feet to the west of the Marianas, while the Ritidian buoy shows almost 3 foot sea heights.

Discussion

Mostly pleasant weather is in store for the Marianas, isolated showers are expected through the forecast period. Island induced thunderstorms are possible for Monday. A weak trough is anticipated to gradually move into the region around the middle of the week. Probability of Precipitation (POPs) are expected to hover around the 20 to 30 percent range. Showers may linger through the rest of the week.

Marine

Light to gentle trade winds will prevail across the region through Wednesday, then become gentle to moderate. Combined seas of around 3 feet will gradually build up to around 5 feet by Tuesday night. This will be due primarily to trade and northerly swells, along with localized wind waves, strengthening around midweek. Surf along all reefs are currently below 5 feet. The risk of rip currents is low on all reefs. Surf may build around the middle of the week and allow the risk of rip currents to increase to moderate along east facing reefs. A moderate risk of lightning will remain through Monday, then become moderate again around Wednesday.

Eastern Micronesia

The dry trade-wind pattern has eroded across eastern Micronesia this afternoon. This is due to a weak Inter-Tropical Convergence Zone (ITCZ) over the area combined with strong upper-level divergence and a couple of weak trade-wind troughs moving through. The first of the troughs is now east of Pohnpei with increasing convection seen moving over the island. POPs were increased to the 50% range for tonight as the trough moves through. For Kosrae, shower coverage looks to remain lower, though POPs were increased to cover low-end scattered showers (30%) through Monday. Monday evening is the time frame when the ITCZ looks to become most active. Since the location of the ITCZ has become more obvious, decided to go ahead and increase showers to numerous across Pohnpei and Kosrae Monday night into Tuesday. However, heavy rainfall is not expected at this time. For Majuro, the bulk of the convection looks to remain south of the atoll, so kept showers scattered through the forecast period. Isolated thunderstorms are also expected at all three forecast points through Tuesday night for Kosrae and through Wednesday for Pohnpei and Majuro. By midweek, the ITCZ looks to lift northward, allowing a drier pattern to move into Kosrae Wednesday and into Pohnpei and Majuro Thursday.

No major changes to the marine forecast. Combined seas of 5 feet or less and light to gentle trade winds are expected to continue through the week.

Western Micronesia

Scattered showers and isolated thunderstorms are moving into Palau this evening as a broad and weak surface trough passes nearby. This trough has shifted slightly further south then previously expected so showers are isolated at Yap, but convergent flow north of the trough is starting to produce scattered showers and isolated thunderstorms just north 10N, from 138E to 143E, passing near Ulithi. Model guidance shows this area of showers expanding into Yap later tonight as the area of convergence strengths. Models then show the area of convergence weakening Monday morning and then briefly rebuilding Monday night as the surface trough moves west of the islands and then starts to lift northwest. As the trough moves away, a light to gentle trade-wind will continue across Palau and Yap, with a slight decrease in the potential for showers and thunderstorms overall through Tuesday night. However, since winds will be on the lighter side, there is the potential for island-effect showers and thunderstorms during the late morning to afternoon hours, especially at Palau, as showers start to develop over the island and then are pushed into the western coastal waters, so kept the potential for showers around 20% to 30%. Starting Wednesday, an ITCZ fragment, or a trough breaking off of the ITCZ in eastern Micronesia, is expected to move into Yap and Palau, increasing the potential showers and thunderstorms through Friday to around 30% to 40%.

At Chuuk, satellite imagery shows partly cloudy skies and isolated showers across most of the State. A trough, along the leading edge of of the ITCZ in eastern Micronesia is expected to drift westward overnight. Models guidance suggest the potential for showers will increase slightly from 20% to 30% after midnight, but the main potential for showers and thunderstorms will be Monday through Tuesday, with the potential of showers increasing to 40% to 50% for that time period as the ITCZ extends into Chuuk State from Pohnpei. Though winds are expected to be light to gentle for most of the week, gusty winds may be possible near showers. Around Wednesday, the ITCZ is expected to lift northward, this will decrease the potential for showers to around 30% across Chuuk State trough Friday.

Altimetry data shows benign seas of 2 to 3 feet near Yap and Palau and 3 to 4 feet near Chuuk. Combined seas are expected to increase to 3 to 5 feet around the middle of the week when a pulse of northerly swell moves through the region.

GUM WATCHES/WARNINGS/ADVISORIES

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