366 FXPQ50 PGUM 030920 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 720 PM ChST Thu Aug 3 2023 .Marianas Synopsis... Island convection is producing afternoon showers and isolated thunderstorms. A weak circulation is south of Guam centered near 9.5N145 this afternoon and a surface trough is slowly approaching the Marianas from the East. A fragmentary Monsoon Trough extends from the circulation southeastward across Chuuk State to end near EQ170E. Ipan Buoy shows a 3-foot east trade wind swell while a northwest swell from distant Typhoon Khanun is still arriving at 3 to 4 feet. && .Discussion... The approaching trough will trigger a few showers at times with isolated thunderstorms mainly during the afternoon and evening hours. Otherwise fairly benign conditions prevail across the region through the near term. A transitional wet-season pattern remains over Micronesia without any particularly dominant weather feature. Southwest monsoon flow persists across the Philippine Sea, while light surface winds and spotty areas of showers are seen across most of Micronesia. Typhoon Khanun, northwest of Okinawa, and another circulation southeast of Japan imply that the large-scale pattern could develop into a Monsoon Gyre as described by Mark Lander's 1992 description, and models indicate that Marianas weather could be affected by a wet southwest flow next week. A Monsoon Gyre pattern would feature a broad region of cyclonically-turning (counter- clockwise) surface flow over the northern Philippine Sea, inducing a moist southwesterly flow over the Marianas. && .Marine... Combined seas of 5 feet to near 6 feet and light winds are expected across the marine forecast zones. Northwest swell of 3 to 4 feet is still arriving from distant Typhoon Khanun and Ipan Buoy shows an easterly trade wind swell about 3 feet. Isolated thunderstorms can be expected through Saturday night, especially near the islands during afternoon hours. && .Eastern Micronesia... The eastern extent of the monsoon trough will persist south of Pohnpei through Sunday. Low-level convergence north of the trough will produce a higher chance of showers and isolated thunderstorms at Pohnpei through Sunday. High pressure will keep showers and isolated thunderstorms at Kosrae tonight through Saturday. A surface trough will push across Majuro tonight and bring scattered showers and isolated thunderstorms there. This trough will be the leading edge of a developing ITCZ pattern. The ITCZ will continue to produce a higher chance of showers and thunderstorms at Majuro through Wednesday. This ITCZ pattern will bring a higher chance of showers and thunderstorms at Kosrae Saturday night through Wednesday and Sunday night through Wednesday night at Pohnpei. Another surface trough will bring a higher chance for showers at Kosrae Thursday. && .Western Micronesia... Afternoon surface analysis showed a circulation between Yap and Chuuk, with a monsoon trough stretching from this circulation to near Chuuk. The circulation will dissipate by Friday leaving the monsoon trough to remain. Another circulation will develop on the monsoon trough east of Chuuk by Friday. Models show that the main monsoon trough will establish itself over the Northwest Pacific north of 20N. The circulation will remain over the western half of Micronesia through at least Thursday, drifting slowly westward to north of Yap by that time. Further east...The circulation that will form near Chuuk will bring scattered showers and isolated thunderstorms over that location on Friday. Much of the activity associated with the circulation will remain west of Chuuk as it moves westward. This will allow drier air to cover Chuuk and keep shower and thunderstorms to a minimum Friday night through Sunday. An ITCZ pattern will develop over Chuuk and produce a higher chance of showers and thunderstorms to this location Wednesday night and Thursday. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Simpson/WBA Micronesia: Ziobro