Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
151 FXPQ50 PGUM 230813 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 613 PM ChST Thu May 23 2024 .Marianas Synopsis... Skies this evening are mostly cloudy across Guam, and partly cloudy across the CNMI, though showers are currently isolated across the Marianas this evening. A weak trade-wind trough east of the Marianas is moving westward and is associated with some increased cloud cover and scattered showers. Latest altimetry shows combined seas of 5 to 7 feet. && .Discussion... The MIMIC Total Precipitable Water (TPW) satellite product shows drier air is starting to filter into the Marianas, with current values across the Marianas currently around 2 to 2.3 inches, and becoming 1.5 to 1.8 inches to the east and northeast, behind the trade-wind trough currently just east of the Marianas. We do expect enough moisture will be present for the trough to generate mostly cloudy skies and low-end scattered showers across the Marianas later tonight and into early Friday morning, but the potential for thunderstorms is very low and contained to Guam`s southern waters. The drier air will then spread across the Marianas through the day Friday, decreasing showers and cloud cover through the afternoon. Models then keep the Marianas in a fairly dry trade-wind pattern through the weekend and middle of next week. && .Marine... Moderate winds and combined seas of 5 to 7 feet will slowly continue to decrease and then stabilize this weekend, with winds becoming gentle to moderate and seas around 4 to 6 feet. Some of the showers and thunderstorms south of Guam the last couple of days have lifted northward and clipped Guam`s southern waters this evening. A weak trade-wind trough east of the Marianas will push in later tonight and early Friday morning, extending scattered showers across the Marianas waters, but the slight risk of thunderstorms will remain in Guam`s southern waters tonight, and then diminishing Friday. There is a moderate risk of rip currents along east and north facing reefs. A low risk continues for south and west facing reefs. Surf is expected to fall another 1 to 2 feet along north and east facing reefs this weekend. This should cause the risk of rip currents to become low along north facing reefs this weekend. && .Fire weather... The KBDI will likely continue to rise since so far today no rain has been reported here at the weather office, and not expecting any significant rainfall with any of the showers expected later tonight. Moderate trade winds are still expected for another day, but then will begin to subside this weekend and for much of next week, perhaps easing some of the fire danger concerns, though atmospheric moisture is expected to decrease, potentially allowing relative humidity to decrease over the next few days. && .Tropical systems... The circulation, JTWC Invest 93W, is now southwest of Koror Palau, near 6N133E, and is moving northwest. 93W is expected to continue in this direction into the Philippine Sea, away from Palau. Satellite imagery showed a weakening of overall convection today and models indicating that the overall threat for strong, gusty showers has decreased for Palau. The JTWC still rates 93W as a HIGH (TCFA) for development, meaning TC development is likely within 24 hours, and this is supported by models in the mid- to long-term as 93W continues to move away from Palau. Convergent flow east of 93W will continue to support showery weather far western Micronesia for the next couple of days, but the overall threat for gusty winds and choppy seas is decreasing. && .Eastern Micronesia and Chuuk... A broad trough in the far eastern portion of the region is at the leading edge of a weak convergence zone. This pattern is expected stretch westward across the region starting with Majuro this evening, then Kosrae by Friday, Pohnpei by Friday night, and reaching Chuuk sometime Saturday night. Scattered showers and spotty thunderstorms are to be expected with this encroaching pattern. Then, model guidance shows signs of the Inter-Tropical Convergence Zone (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 Palau and Yap... The last update of the Special Weather Statement (SPS) was sent this evening. Invest 93W is centered about 160 miles southwest of Palau and is on track to continue northwest into Philippine Sea. Satellite imagery showed a weakening of overall convection today and models indicating that the overall threat for strong, gusty showers has decreased for Palau, and even more so for Yap. Convergent flow following the system will maintain showery weather, however, conditions will gradually improve in the next day or so. A ridge moves in Sun-Tue, to further weaken shower potentials, then a transition to a trade-wind pattern ushers in another period of scattered showers around the middle of next week. The Small Craft Advisory for Palau was allowed to expire this afternoon. Mariners should still exercise caution as occasional fresh to strong gusts and choppy seas are still possible tonight. Palau buoys indicate seas are 6 to 7 feet and altimetry data similarly shows a range of 5 to 7 feet for the region. East to southeast winds are moderate (occasional fresh gusts for Palau tonight) then is expected to decrease to gentle to moderate by the weekend as 93W gradually advances farther to the northwest towards the Philippines. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Schank Micronesia: Cruz Tropical: Cruz/Schank