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Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
658 FXPQ50 PGUM 121853 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 453 AM ChST Tue Aug 13 2024 .Marianas Update... Only minor edits to the previous forecast made. Partly cloudy skies and spotty showers expected today. Did speed up the arrival of a surface trough and the potential for scattered showers and isolated thunderstorms for late tonight, based off the latest satellite and model trends, and continuing through Wednesday night. For late week into the weekend, expect a chance of showers and slight chance for thunderstorms as a series of surface troughs pass through the Marianas. Combined seas of 3 to 4 feet from mainly northwest swell, and light to gentle winds prevail through Wednesday morning. Winds and seas look to rise slightly for mid to late week as the easterly flow returns and easterly swell becomes dominant. A moderate risk of rip currents continues along west and north facing reefs through tonight, becoming low on Wednesday. Surf and rip risk looks to build along east facing reefs late week as the easterly swell increases && .Tropical Systems Update... Invest 91W has steadily intensified over the past day and has developed into a tropical depression (TD 08W), centered near 24N137E. Convection continues to flare up and become better organized around the low-level disorganized center (LLCC) and maximum winds estimated to be around 25 kts. TD 08W is expected to intensify further as it turns northward towards Japan, possibly becoming a tropical storm by later today and a typhoon by Wednesday night. && .Eastern Micronesia Update... Only minor tweaks to the forecast were needed. For Pohnpei, showers are expected to be isolated in the AM hours, becoming scattered by the afternoon and overnight. Kosrae is expected to have fair weather due to being in a weak ridge. Majuro can anticipate a weak trough passing through later tonight to bring showers up the borderline between isolated and scattered. Seas remain fairly benign for the region, with combined seas of 3 to 5 feet. Winds are expected to be light to gentle. && .Western Micronesia Update... Only minor weeks to the forecast were needed. For Palau, island effect showers at anticipated for the afternoons due to low winds and the winds that are there are expected to be blowing long wise across the island. This gives convection the maximum time to get started. For Yap, cloud cover was about the only thing needed to be changed, and the POPS for tonight were also dropped due to the ridge being a little more prevalent in the models. For Chuuk, the POPs were increased for tonight and tomorrow, models indicated that the trough that is bringing Weno showers will linger a bit longer. Seas remain fairly benign for the region, with combined seas of 2 to 4 feet. Winds are expected to remain light to gentle. && .Prev discussion... /issued 601 PM ChST Mon Aug 12 2024/ Marianas Synopsis... Light to gentle southeast winds and combined seas of 3 to 4 feet continue across the region. Satellite indicated isolated showers across the Marianas coastal waters with only a shallow buildup of island convective showers. Discussion... Very little change to the forecast. The region continues to be fairly dry and today`s showers were minimal over the island. Winds are expected to turn a bit more easterly with easterly swell becoming the predominant swell around Thursday. Light to gentle winds are expected to continue through the forecast period, but stronger winds are possible with the development of tropical systems along the monsoon trough. Marine/Surf... No significant changes to the marine forecast. 3 to 4 foot northwest swell is expected to decrease by 2 feet starting mid week through the weekend. Starting Wednesday and continuing trough the weekend, east swell is expected to increase from 2 feet to 3 to 4 feet. Predominant swell direction is expected to be easterly by Thursday. Tropical systems... A Tropical Cyclone Formation Alert (TCFA), Invest 91W, located near 23N136E west of Iwo To, is showing good rotation and increasing convection near its low-level center. Surface winds are estimated to be around 18 to 23 knots. Invest 96W, located east of Iwo To, has an exposed low- level circulation center and convection is not well organized. Both these systems are expected to track to the north over the next few days as 95W, which is further north of 96W along the monsoon trough, heads towards northern Japan. Eastern Micronesia... Pohnpei had island-effect showers during the afternoon, as winds remained weak due to the ridge of high pressure that is extending through central and western Micronesia. A pair of troughs, one south of Kosrae and the other moving across the Marshall Islands also brought scattered showers to Kosrae and Majuro earlier today, but these troughs are starting to push westward and allowing showers to become isolated at both locations this evening. As the ridge slowly weakens and drifts westward, easterly winds are expected to slowly become gentle to moderate across the region, however it looks like winds will be weak enough Tuesday for more island-effect showers over Pohnpei during the afternoon. The trough south of Kosrae is expected pass south of Pohnpei Tuesday as well which will help to spread scattered showers into the coastal waters of Pohnpei, while the trough in the Marshall Islands will move out of west of the Marshall Islands tonight should pass well north of Kosrae, keeping showers isolated at Kosrae Majuro through Tuesday. Another series of troughs is expected to move across the Date line starting Wednesday which will increase the potential for showers and thunderstorms across the region for the latter half of the week. Benign marine conditions are expected this week, with combined seas mainly around 3 to 5 feet, potentially reaching up to 6 feet at Kosrae this weekend. The primary swell remains out of the east to southeast, while light to gentle winds will become gentle to moderate easterly winds across the region around Wednesday or Thursday. Western Micronesia... A ridge of high pressure stretches across the Marianas into the region. Weak convergence in the south-southwesterlies will increase clouds and showers at times, but are still expected to be isolated to scattered for Yap and Palau. Similar to the past several days, the light and variable winds will allow for island-effect showers to develop in the afternoon. After seeing the development of the afternoon convection over Palau and attributing it to the relatively larger land mass, added a slight chance of thunderstorms during those times as well. The ridge is expected to weaken and shift northwestward, allowing for trade showers to develop at times for Yap and Palau starting late this week. A weak trade- wind trough is east of Chuuk and will continue to propagate westward, bringing scattered showers to Chuuk Tuesday. Chuuk will continue to see periods of scattered showers through the week and over the weekend with passing trade-wind troughs. Benign marine conditions are expected over the next several days, comprised of light to gentle winds and combined seas 2 to 4 feet. Seas near Chuuk are expected to build to 5 feet later this week with increasing trade swell. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Slagle/Hong Micronesia: Bowsher/Schank/Cruz