Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
650 FXPQ50 PGUM 170722 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 522 PM ChST Sat May 17 2025 .Marianas Synopsis... Radar indicates isolated showers throughout the Marianas. Satellite imagery show mostly cloudy skies over the region. Ritidian buoy and altimetry shows 4 to 6 feet for combined seas. && .Discussion... No major changes were made to the forecast. A dry trade-wind pattern remains firmly intact across the Marianas. CIMMS MIMIC suggests the Marianas has about 1.6 to 1.8 inches of Precipitable WATer (PWATs). Time heights also confirm a deepening moisture layer, especially in the upper atmosphere and the mid atmosphere by end of next week. These are the first signs that the transition to wet season may be starting. && .Marine... Combined seas of 4 to 6 feet will keep marine conditions fairly benign. Seas may diminish by about a foot near the end of the week. Winds are expected to remain moderate through next week. A moderate risk of rip currents remains along east facing reefs, with a low risk along all other reefs. && .Fire weather... 0.05 inches of rain fell so far today at the Guam International Airport. The KBDI remains at 745, which is in the high category due to winds remaining below the 20 mph threshold. Both winds and relative humidity values look to remain below Red Flag Warning criteria the next few days. A wetting rain is not expected for at least the next several days, and the KBDI is expected to continue to rise. && .Eastern Micronesia... A generally wet pattern produced by the ITCZ building overhead, is expected to last for at least the next few days. A peak in convective activity is expected over Pohnpei and Kosrae tonight, with showers likely to be heavy over Pohnpei, in addition to isolated thunderstorms and strong gusts expected. A slow taper down in shower coverage is expected by early next week. Patchy on-and-off showers are expected at Majuro for much of the forecast period, as a more compact portion of the ITCZ lingers upstream. Combined seas of 5 to 6 feet near Pohnpei and Kosrae, and 6 to 7 feet near Majuro, are expected to taper down a few feet by the middle of next week, as trade swell and localized wind waves decrease. && .Western Micronesia... A fairly unsettled, but more disorganized pattern continues across the region. Trade-wind convergence north of the near-equatorial trough (NET) maintains scattered showers near and south of Palau this evening, which should diminish to isolated around midnight as convergence and associated showers shift westward. A quieter trade- wind pattern continues for Yap, which remains in a relatively drier environment with MIMIC TPW showing precipitable water amounts of 1.8 to 1.9 inches just upstream. However, there are some showers moving into the area. Himawari visible satellite shows a series of outflow boundaries pushing east-northeastward into the region this afternoon, from out of a broad area of trade-wind convergence and associated convection over western Chuuk State and eastern Yap State. Most of these showers look to stay south of Yap Proper as they cross the area tonight, but may provide some fresh to strong gusts out of the east to east-southeast. Otherwise, Yap can expect gentle to moderate trades tonight, becoming moderate to fresh Sunday through early next week. Further east, an area of disorganized trade-wind convergence is generating scattered showers near the main islands of Chuuk, with numerous showers just further east across much of eastern Micronesia. Model guidance and satellite trends suggest most of these showers, associated with the ITCZ, will remain south and east of Chuuk Lagoon overnight and tomorrow. However, scattered showers can be expected to continue at least through the overnight due to more localized trade convergence in the area. Buoy and altimetry data show combined seas of 4 to 6 feet across the region, increasing to near 7 feet east of Palau, possibly associated with higher wind waves from the lines of convection further east. Seas may decrease by a foot or so across the region by the middle of next week with a slight weakening in trades, wind waves, and swells. For the next few days, however, trade winds will mostly remain gentle to moderate across the region, becoming moderate to fresh at times near Chuuk and Yap. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Bowsher East Micronesia: Montvila West Micronesia: DeCou