Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
992 FXPQ50 PGUM 120733 CCA AFDGUM Area Forecast Discussion...CORRECTED National Weather Service Tiyan GU 533 PM ChST Mon May 12 2025 .Marianas Synopsis... A Red Flag Warning remains in effect through at least Thursday afternoon. Satellite imagery shows isolated showers. Ritidian buoy shows combined seas of about 5 feet. && .Discussion... The dry trade-wind regime remains intact and is expected to continue through Monday. The time heights suggest there is still a fairly dry mid level through about Wednesday, and suggest a moistening mid- level layer though the rest of the forecast period. A trade-wind trough will be what brings in some moisture into the region. The trough may be enough to spark some showers. The winds are expected to increase while the trough passes through the region, and may diminish below 20 MPH near the weekend. && CORRECTED A WORD WRAP .Marine... Moderate trade winds will preveil through the week with 2 exceptions of moderate to fresh winds during the day on Tuesday and Wednesday. Combined seas of 5 to 7 feet will build to between 6 and 8 feet as a east-northeast swell will move into the region tonight. The secondary swell is anticipated to diminish by the weekend. Combined seas are expected to fall to 4 to 6 feet by the weekend. Sea conditions will remain benign through the period. There will be a moderate risk of rip currents along north and east facing reefs of the Marianas through the middle of this week. A secondary swell will arrive in the region tonight, which should allow surf along north and east facing reefs to rise by a foot. The risk of rip currents is expected to remain moderate through the middle of the week before falling near the end of the week. && .Fire weather... No rain has fell so far today at the Guam International Airport. The KBDI remains at 733, which is in the extreme category due to daytime winds of 15 to 25 mph. The Red Flag Warning was extended through Thursday due to model guidance suggest the winds will remain above the threshold of 20 mph. Terrain forcing of winds and occasional gusts could make fire fighting drastically harder. The fire danger is expected to become critical during the daytime hours, with afternoon relative humidities expected to drop below 60 percent, and elevated winds, especially in higher terrain. 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 seasonal trade-wind regime is expected to continue at all three forecast locations for much of the forecast period. Mostly dry conditions at Pohnpei, and low-end scattered showers at Kosrae and Majuro expected overnight, followed by a return of consistently patchy showers and elevated winds once a convergence zone rebuilds in the second half of the week. Combined seas of 5 to 7 feet near Pohnpei and Kosrae, and 6 to 8 feet near Majuro, are expected to persist as such for much of the week, before tapering down slightly across the region by the weekend. && .Western Micronesia... A wetter pattern looks to develop for Palau, and to some extent for Yap, in the day 2 through 5 time frame Wednesday through Saturday. Palau: This is evident in the latest GFS Galvez-Davison Index(GDI) image loop, as GDIs climb towards 60, occasionally surpassing it, which based upon close observation over the last ~3 years, it "seems" that when the GDI climbs into the upper 50s, locally heavy rainfall develops (typically resulting in rainfall amounts near an inch, if not more). Yap: You look to be on the edge of the moisture gradient the next several days, with GDIs "crashing" from the upper 50s to less than 30 within 2 degrees of latitude as one heads north. As such, the forecast oscillates between isolated and scattered (slight chance versus chance probabilities) in the forecast. Chuuk: Similar to Yap, the moisture gradient, as seen in the GDI, will also oscillate between the mid to upper 50s (currently and towards the weekend), with drier air moving into the region Tuesday, when showers become isolated in coverage, before increasing back into the scattered range for Thursday, increasing further to numerous probabilities for Saturday. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...Red Flag Warning until 4 PM ChST Tuesday for GUZ001. MP...None. Marianas Waters...None. && $$ Marianas: Bowsher East Micronesia: Montvila West Micronesia: Doll