FXPQ50 PGUM 050838 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 638 PM ChST Wed Oct 5 2022 .Marianas Synopsis... Light surface winds due to a trough axis perched across the Marianas and daytime heating led to island-effect convection across all 4 islands from Guam to Saipan this afternoon. Parts of central western Guam recorded 2-3 inches of rain while parts of Saipan saw around 1 inch of rain. Conditions have stabilized locally, but heavier showers and thunderstorms are found farther north along a line stretching east-west over Anatahan. Buoys and altimetry data show combined seas of 3 to 5 feet across the region. && .Discussion... Short term weather will continue to be dominated by a light wind pattern as the surface trough sits over the region. A slightly unstable pattern will be generally supportive of isolated thunderstorms, but, similar to today, afternoon island heating and light winds coupled with a moist airmass of around 2.2in PWAT, as noted in MIMIC TPW favors increasing showers over the islands Thursday afternoon. Worth noting, yesterday`s runs of the the Hi-Res WRF performed very well in depicting the timing and location of today`s island-effect convection, even their development over all 4 islands. For tomorrow, the WRF still highlights this potential, but to a slightly lesser extent. The WRF and global models differ slightly on wind direction with their depiction of the trough axis location varying slightly north to south. However, the more likely location of convective development will be on the downwind side of the islands. Heading into the weekend and next week, showers gradually become more favorable with POPs increasing to around 50 pct late weekend as the broad trough, and a potential circulation, push off to the west. && .Marine... Combined seas will hover between 3 and 5 feet the next few days with the combination of a small easterly swell and northerly swell. The east swell will fall about a foot Friday. Surf will maintain a moderate risk of rip currents the next few days. && .Tropical systems... Models continue to show circulations slowly forming along the surface trough in the coming days though each model run changes their placement. Through the weekend, both the GFS and the ECMWF show an east-west trough perched along 15N. The models diverge along their separate paths into next week with the GFS still being the more aggressive in developing a circulation east of the far northern Marianas and moving it WNW into the northern Philippine Sea while the more conservative ECMWF passes a weaker circulation westward across the lower Marianas. While the forecast package continues to reflect a more conservative approach concerning the winds, both model solutions point to a wetter Marianas for next week. && .Eastern Micronesia... A semi-active Inter-Tropical Convergence Zone (ITCZ) stretches from near Majuro west-northwestward to end north of Pohnpei. Latest guidance shows this feature strengthening slightly as it undulates north and south over the next couple of days. The ITCZ is generating scattered showers near Majuro that should continue through the night. A couple of weak trade-wind troughs are seen traversing the area as well. The first of these troughs will move into Pohnpei later this evening, resulting in increasing showers near midnight. Another trough, farther east, will move into Kosrae as well, resulting in scattered showers and isolated thunderstorms there as well. As the ITCZ becomes a bit more active and continues to meander north and south, it is expected to maintain a wet pattern over the region through the middle of the coming week, with the exception of Kosrae, where it appears that the ITCZ will remain north of the state beginning Tuesday. Combined seas of 4 to 6 feet are expected to continue across the region for the next several days. Light to gentle east to southeast winds are expected to continue over the next several days. && .Western Micronesia... A fairly dry pattern is now in place across Yap and Palau. This dry pattern is expected to continue through the weekend for Yap and into next week for Palau. Late in the week, a monsoon trough looks to develop to the north of Yap, extending from the Philippines into the Marianas. Models indicate this feature will drift south over the weekend, bringing increasing showers to Yap as early as Monday, then increasing over the next couple of days. By Tuesday night, this monsoonal flow looks to move into Palau as well, bringing an end to the dry pattern there. Currently, winds look to remain gentle with occasional moderate winds early next week for Yap. Farther east, dry conditions persist at Chuuk this evening. However, an approaching weak trade-wind trough looks to bring increasing showers to Weno near midnight. Slow movement of this trough looks to maintain scattered showers there through Thursday night. Once this feature exits the region, a weak southeast flow sets up with divergence evident in the low levels and possibly upper-level convergence. This will result in a dry pattern into next week. This dry pattern looks to break down by the middle of next week as weak troughs move into the region resulting in a band of convergence over the state. Combined seas of 3 to 5 feet and primarily light to gentle winds are expected to continue over the region through the weekend. Occasionally moderate winds are possible at Palau Thursday as a weak surge moves through to the south. Occasionally moderate winds are also possible at Yap early next week as the monsoon trough drifts south. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Aydlett Micronesia: Kleeschulte