Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
479 FXPQ50 PGUM 051734 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 334 AM ChST Sat Jul 6 2024 .Marianas... .Short-Term Update... A surface trough crossing southern Guam waters has hastened in its forward motion, with an expected departure to the west in the first few hours of the forecast period. As such, dropped shower coverage down to isolated across the region. Otherwise, the weather and marine forecasts remain unchanged. && .Eastern Micronesia... .Short-Term Update... Active weather continues for Pohnpei and Kosrae while Majuro weather is gradually settling down a bit for the near term. Majuro will see a moderate to fresh trade-wind surge though, and GFS model guidance indicates combined seas will build into the 5 to 7 foot range, and probably some bigger seas over the northeast RMI. These moderate to fresh sea conditions will likely develop toward Kosrae and Pohnpei by next week. && .Western Micronesia... .Short-Term Update... Only minor changes were made to the forecasts. Conditions will be changeable over far Western Micronesia the next several days, and some showers will arrive at Chuuk from the east at times, especially over this weekend. Overnight ASCAT surface winds analysis indicates a disturbance is centered roughly near 5N148E, far southwest of Chuuk. Otherwise, a complex troughing pattern is sprawled over the region, and a weak ridge of high pressure is over the Philippine Sea. && .Prev discussion... /issued 550 PM ChST Fri Jul 5 2024/ Marianas Synopsis... Satellite imagery shows partly cloudy skies and isolated showers across the Marianas this evening, with a weak trough approaching the southern waters of Guam from the southeast. Winds are gentle to moderate, with altimetry and buoy data showing combined seas around 3 to 5 feet. Discussion... Weather across the Marianas is fairly dry this evening, but a weak trough southeast of Guam will move up into the area later tonight and into Saturday, and then pushing west of the islands Saturday night. Scattered showers are expected to move into Guam after midnight and then spread northward into Rota Saturday, while model guidance currently keeps most of the showers south of Tinian and Saipan. Due to lack of upper-level support and the fact no lightning as been detected within the trough by the Global Lightning Detection (GLD) network so far today, did not mention thunderstorms in the forecast for tonight and Saturday. As the trough moves off to the west Saturday night, showers will decrease back down to isolated, with partly to mostly cloudy skies through early next week as most of the active weather features are expected to remain south of the Marianas, occasionally clipping the Marianas around the middle of next week. Previous forecast have mentioned isolated thunderstorms for Sunday and Sunday night as models shows the Tropical Upper-Tropospheric Trough (TUTT), currently near Wake Islands, nearing the Marianas around Sunday. Decided to keep isolated thunderstorms in the forecast at this time, but there are signs that the risk for thunderstorms may be decreasing. First, models are now showing no notable surface features, such a trough near the Marianas around Sunday, which would help to limit the development showers that could grow into thunderstorms. Also, global models show the TUTT weakening over the next couple of days, which also points to a diminishing risk for thunderstorms on Sunday. Marine... Gentle to moderate trade winds and combined seas of 3 to 5 feet will continue through at least Wednesday. Through Saturday, most of showers within the coastal waters will be within Guam and Rota waters due to a passing trade-wind trough currently southeast of the Marianas. There is the potential for isolated thunderstorms Sunday as the Tropical Upper-Tropospheric Trough (TUTT) east of Wake Island slowly drifts westward towards the Marianas and is expected be near the Marianas around Sunday. There are signs that the potential for isolated thunderstorms may be decreasing, and this may be reflected in future forecasts as the exact timing and strength of the TUTT and any surface features becomes more certain Eastern Micronesia... Expect scattered showers and isolated thunderstorms tonight for Majuro. Active weather near Majuro will then dissipate as divergence aloft shifts west. A trade-wind trough near Kosrae was producing showers for Kosrae this morning, and has not moved much. The near- equatorial trough has extended further east to Pohnpei and maybe even slightly further east to near Kosrae. Scattered showers and isolated thunderstorms are expected through the weekend at both Pohnpei and Kosrae and possibly until the middle of next week. Altimetry reported 3 to 5 ft near Pohnpei and Kosrae. Gentle to moderate trade winds are expected through out the forecast period. Sightly elevated winds are expected tonight at Majuro as the weakening convective system moves across their waters. Seas are expected to increase by 1 to 2 feet starting early next week through at least middle of next week. Western Micronesia... For Chuuk, expect scattered showers tonight as a trade-wind trough crosses the island. Also an upper-level low is moving across and may fire off some thunderstorms. Tomorrow`s weather looks better for Chuuk, so went with isolated showers, as models predict a flattening out of the trough by tomorrow. Latest visible satellite shows spotty showers across Koror and Yap with a near-equatorial trough or possible weak circulation to the east of Koror. Expect scattered showers and isolated thunderstorms tonight. By tomorrow expect isolated showers as divergence aloft moves out of the region. A few upticks in showers are expected in the following days, but nothing significant, will possibly see some island convection showers and thunderstorms with light and variable winds forecasted for the next few days. Altimetry reported benign seas of 2 to 4 feet near Palau and Yap. Expect light and variable winds for Palau and Yap and light to gentle for Chuuk through out the forecast period. Seas for Chuuk are expected to increase by 1 to 2 feet starting early next week, but for Palau and Yap, seas are expected to remain at 2 to 3 feet. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Montvila/Schank Micronesia: Simpson/Hong