399 FXPQ50 PGUM 040850 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 650 PM ChST Fri Aug 4 2023 .Marianas Synopsis... The latest satellite loop shows showers are decreasing in coverage. However, a light wind pattern will continue through the weekend, with late morning through late afternoon showers and maybe a thunderstorm or two will continue to develop near the western coasts. Then, as a tropical disturbance approaches, shower and thunderstorm will increase by the middle of next week. Until then, seas continue to be in the 4 to 5 foot range, with a water temperature of 86 degrees at Ipan. && .Discussion... The forecast remains largely unchanged through the weekend. Given the light wind pattern, convection will likely fire up by late morning near the western and/or southwestern coasts of the Marianas, continuing through late afternoon, then decreasing in coverage as we near sunset. The real potential weather-maker to keep an eye is a tropical disturbance, known as Invest 94W by the Joint Typhoon Warning Center (JTWC), is forecast by various models to approach the Marianas by Tuesday or Wednesday next week, gradually strengthening as it does so. More on this is mentioned in the tropical section below. At this time, 94W's main impacts to the Marianas looks to be increasing rainfall potential, some of which may be heavy, especially for Guam and Rota. Winds will strengthen some, but won't become too strong. Overall, expect winds to be similar to what they were a week or so ago as a system passed between Guam and Yap, when we had increased rainfall coverage and intensity, with a few higher gusts near heavier showers. With all guidance showing this potential, POPs (Probability of Precipitation) were increased to likely (60 or 70 percent potential), while adding in some locally heavy rainfall wording. The zones were also split into two zones (Guam and Rota, Tinian and Saipan) to account for different timing of this potential and wind shift times. Temperatures were also lowered to account for this. && .Marine... Late morning through mid to late afternoon shower and thunderstorm development seems probable through the weekend given the light wind pattern, contributing to "island-effect" convection. Overall, the western and southwestern coasts of the Marianas seem to be most favored, but the southern half of Guam could see this venture into central or southeastern areas from time to time, due to the higher terrain and longer length of the island (orographical effects with possible outflow boundary interactions). Otherwise, seas of 4 to 5 feet with a mixed swell look to hold through at least Monday, then gradually increase for the middle to end of next week. During this time (the latter half of next week), light to gentle winds will become gentle to moderate, potentially higher depending how an approaching disturbance evolves. && .Tropical... The models continue to advertise Invest 94W will gradually strengthen, very slowly, over the next several days as it heads towards the Marianas. Where it'll track and at what strength remains unclear, but at this time it doesn't look to be too significant of a system as it passes through our region. Shower and thunderstorm potential and intensity will increase if current model solutions hold. && .Eastern Micronesia... A circulation known as Invest 94W by JTWC is located near 5N155E. A monsoon trough stretches from the circulation to south of Pohnpei at EQ163E, which is slightly westward since yesterday. An ITCZ fragment is between Majuro and Butaritari this afternoon. Converging east and southeast winds are causing showers in patchy areas over Eastern Micronesia; some near Kosrae but quite a bit more just east to southeast of Majuro. The ITCZ will persist during the next few days with patchy showers and isolated thunderstorms at times for Pohnpei, Kosrae and Majuro. Majuro Kalo Buoy shows combined seas ranging from 3 up to 6 feet, mainly trade wind waves but a small south-southeast swell will show up at times in the coming days. && .Western Micronesia... A circulation, now Invest 94W, near 5N155E this afternoon will be the dominant weather feature in the coming days. A monsoon trough extends west and southeast from the circulation. Deep convection has been flaring near the circulation this afternoon, more so than in previous days, and that indicates further development is likely. I already needed to update the Chuuk forecast:) Models differ on the details but trends for further development of 94W are expected. The moist southwest monsoonal flow is expected to reform across Yap and Palau over the weekend. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Doll Micronesia: Simpson