Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
975 FXPQ50 PGUM 220920 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 720 PM ChST Wed May 22 2024 .Marianas Synopsis... A pleasant trade-wind pattern persists across the Marianas with only passing low-level clouds and few, if any, showers. Winds have occasionally been gusting to around 30 mph with the robust trade winds. South of Guam, along 10N, a band of deeper moisture stretches eastward from Yap State to north of Chuuk. This moisture band, with its attendant showers and thunderstorms, is showing a steady westward motion with upper-level southwesterlies pushing cirrus northward into the Marianas. Latest altimetry shows combined seas of 6-9 feet. && .Discussion... The dry trade-wind pattern across the Marianas will largely continue through the weekend with little change other than weakening trades. The east-west band of showers and thunderstorms between 9N and 12N will remain to our south the next several days with showers sliding westward. Model guidance still favors a slight northward shift of moisture Thursday-Friday, depicting showers and thunderstorms reaching up into southern Guam waters for that time frame. For now, and based on model consensus, Guam is kept north of the showers and thunderstorms, but it is still a very narrow margin. && .Marine... Bumped up short-term seas 1 to 2 feet based on EC wave data which is running slightly higher than GFS-wave and WW3 data. A late-afternoon altimetry pass indicating 8-9 ft seas across and just east of the Marianas provided the much-needed ground truth verification for some forecast decisions. Decided to extend the high risk of rip currents into Thursday morning, and then the modeled downtrend in easterly swell should allow surf and resultant rip currents to subside. This trend will continue into the weekend and early next week with seas falling to around 5 ft by Sunday. && .Fire weather... The KBDI will likely continue to rise since showers today amounted to less than 0.20 inches. Moderate to fresh trade winds are still expected for another day, but then will begin to subside by the weekend and for much of next week, perhaps easing some of the fire danger concerns. && .Tropical systems... Satellite trends show a consolidating 93W sitting SE of Palau near 6N136E. JTWC now rates it as a medium for development, meaning development into a significant TC is likely, but beyond 24 hours. Model guidance still supports a passage near or just south of the main islands of Palau sometime Thursday then heading WNW into the PI Sea as it develops further. 93W will bring periods of heavy showers and gusty winds to Palau through Thursday. && .Eastern Micronesia and Chuuk... A mild weather pattern is in place across eastern and central Micronesia this evening. Spotty showers persist around Chuuk, due to weak convergence in the trades. A weak Inter-Tropical Convergence Zone (ITCZ) is expected to gradually rebuild across the region over the next several days, with scattered showers building into Majuro late tonight. Isolated to scattered showers are expected through the weekend, then model guidance shows signs of the ITCZ strengthening early next week. Benign marine conditions are expected over the next several days. Moderate trade winds become gentle to moderate this weekend. Combined seas are expected to be between 5 and 7 feet. && .Western Micronesia for Yap and Palau... JTWC`s Invest 93W was upgraded to Medium, as satellite and model trends point to a steady intensification over the next 24 hours. While potential development into a significant tropical cyclone is possible, it is likely to be outside of the region, when it is further towards the Philippines. Over the past 12 hours, 93W still appears as a broad circulation (centered southeast of Palau), however it is gradually consolidating. Also, the upper-level trough to the northwest is still influencing this system, favoring a band of thunderstorms west and northwest of Palau. The trajectory of 93W is still expected to pass just south of the main islands of Palau late tonight, then continuing northwest into the Philippine Sea. Periods of heavy rainfall and gusty winds are still possible for Palau through Thursday, possibly Thursday night as well. Rainfall amounts are estimated to be 3 to 5 inches over the next 36 hours. For Yap, the brunt of showers, thunderstorms, and gusts was experienced today. GPM/IMERG-early (satellite-derived rainfall estimates) indicates 1.5-2.5 inches over the past 24 hours. Locally heavy showers and gusts are still possible through tonight, then, as 93W advances further away into the Philippine Sea, showers will still remain in the area but will be derived from trade convergence trailing this system. A Small Craft Advisory was issued for Palau late tonight through Thursday based on how models are handling the passage of 93W to the south. One model, the GFS, shows sustained winds just barely meeting criteria, however decided to issue this advisory knowing that heavier showers tied with this circulation are bound to bring stronger gusts that would create hazardous conditions for mariners. Altimetry and Babeldaob buoy indicates combined seas are 4 to 6 feet. East to southeast winds are moderate to fresh over the next day or two, then will decrease to gentle to moderate by the weekend as 93W moves further to the northwest. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...High Rip Current Risk until 6 PM ChST this evening for GUZ001. MP...High Rip Current Risk until 6 PM ChST this evening for MPZ001>003. Marianas Waters...None. && $$ Micronesia: Cruz Tropical: Aydlett