


Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
308 FXPQ50 PGUM 181915 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 515 AM ChST Sat Jul 19 2025 .Marianas Update... Satellite shows cloudy skies over much of the region, from deeper convection to the south. This is also bringing light, stratiform rain over Guam and Rota this morning. The main change was to increase shower and gust potentials today. Convergence in the trade-wind pattern and the TUTT to the west, are expected to bring scattered showers, to at times numerous showers, and isolated thunderstorms today with gusts to 25 mph near heavier showers. Combined seas of around 5 feet may increase a foot Monday when another pulse of west-southwest swell reaches the Marianas. If the swell comes in a bit higher than projected, seas could rise up to 5 to 7 feet next week, possibly increasing the rip risk to west and south facing reefs as well. && .Eastern Micronesia Update... Showers are expected to increase slightly more at Pohnpei and Kosrae today due to a broad trough slowly moving in from the east, bringing patchy showers to Kosrae this morning and at Pohnpei in the afternoon. The Intertropical Convergence Zone (ITCZ) remains the primary trend-setter for much of the forecast period, with a series of weak troughs expected to traverse the region as said ITCZ reinvigorates over the coming days. In addition, the marine forecast remains unchanged as well. && .Western Micronesia Update... A leading edge of a significant southwesterly monsoon push has been observed on satellite imagery and the most recent scatterometer passes overnight, very strong sustained winds, occasional gale-force gusts and choppy seas that will be hazardous to small craft until late morning today in Palau Waters. As such, a Small Craft Advisory has been issued for Palau waters through late this morning. Winds and seas are then expected to taper down slightly in the afternoon, but gusts are expected to occasionally be near gale-force in the early evening hours, before improving steadily thereafter. Other than that, only a slight decrease in PoPs was introduced to Chuuk through tonight, but showers are still expected to remain scattered in nature throughout the day. The marine forecast remains unchanged for all three locations. && .Prev discussion... /issued 502 PM ChST Fri Jul 18 2025/ Marianas Synopsis... Satellite imagery shows overcast skies and radar imagery shows scattered showers and isolated thunderstorms over the Marianas. Altimetry shows 4 to 5 feet, and both buoys confirm these seas. Winds are light to gentle. Discussion... A trade-wind convergence zone is interacting with the Tropical Upper Tropospheric Trough (TUTT) and producing showers and thunderstorms over the Marianas. The convergence zone is expected to pass by over the next 24 hours or so. Over the next few days, trade-wind troughs are expected to provide the support to the TUTT that is needed to keep showers and thunderstorms in the forecast. This support is anticipated to diminish by Tuesday. Showers are anticipated to clear up near the middle of next week. Marine... Gentle to moderate east winds will continue through the beginning of next week. Seas are expected to be around the 4 to 6 feet. Surf along east facing reefs are 5 to 7 feet, and are producing a moderate risk of rip currents. Surf along all other reefs are below 5 feet producing a low risk of rip currents. A west-southwest swell may make its presence known near the beginning of next week. This may cause the surf to rise enough to produce a moderate risk of rip currents along south and west facing reefs. Eastern Micronesia... The Inter-Tropical Convergence Zone (ITCZ) has weakened and fragmented across eastern Micronesia. The main players for the region over the next couple of days will be a couple of trade-wind troughs traversing the area. The first of these troughs is approaching Kosrae and should bring increased convection to the island later this evening. As this trough passes through, it looks to move south of Pohnpei, leaving only isolated showers there for the next couple of days. The next trough is seen east of Majuro. This trough is interacting with a fragment of the decayed ITCZ, bringing scattered showers and isolated thunderstorms to Majuro tonight. Latest model guidance shows the ITCZ reinvigorating over the weekend. This will bring increased convection across the region into next week. Little change made to the marine forecast. Light to gentle winds are on tap for Pohnpei and Kosrae through through the middle of next week. For Majuro, moderate to fresh winds tonight are expected to become gentle to moderate over the weekend. Combined seas of 5 to 7 feet at Majuro will slowly subside to between 4 and 6 feet early next week. For Pohnpei and Kosrae, seas of 3 to 4 feet are expected through the middle of next week. Western Micronesia... Expect an active pattern across western Micronesia through the weekend as the monsoon trough meanders near Palau and Yap. Moist, converging westerlies and southeasterlies along the trough will result in scattered to numerous showers and thunderstorms through Saturday night for Palau and through Sunday night for Yap. Heavy downpours and gusty winds will be possible with stronger showers and thunderstorms. Conditions will slowly improve next week as the monsoon trough is dragged north and west as the tropical disturbance Invest 96W creeps towards the northern Philippines and Taiwan, with surface ridging trying to build in its wake. For Chuuk, a series of surface troughs will pass through the lagoon through Saturday, with periods scattered showers and isolated thunderstorms. A surface ridge passing through late weekend will help suppress shower development. As next week progresses, moist southerly flow will bring an increasing potential for showers and thundestorms. Combined seas of 4 to 6 feet are expected for Palau and Yap, comprised of a west to southwest monsoon swell and weaker easterly trade swell. Winds will be gentle to moderate, with fresh to strong gusts near heavier showers and thunderstorms. Winds will become light to gentle and seas will lower to 2 to 4 feet next week as the surface ridge builds in and the monsoon swell subsides. Combined seas of 2 to 4 feet are expected in Chuuk waters for much of the forecast period, driven by the primary trade swell. Light to gentle winds look to lower and become light by later Sunday. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas Update: Cruz East/West Micronesia Update: Montvila Marianas: Bowsher East Micronesia: Kleeschulte West Micronesia: Slagle