289 FXPQ50 PGUM 082223 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 823 AM ChST Sat Oct 9 2021 .Marianas Synopsis... The Marianas are mostly cloudy this morning, and radar shows scattered showers approaching Guam and Rota from the east. Gentle to moderate east to southeast winds are seen across the region, while combined seas are between 4 and 5 feet at the Ipan buoy. Well west of the islands, a large monsoon depression, JTWC Invests 93W/94W, continues to slowly develop north of Yap and Palau, and a monsoon trough extends eastward from there south of Guam and on to a tropical disturbance, Invest 95W, situated south of Wake Island. Invests 93W and 94W are now the subjects of twin Tropical Cyclone Formation Alerts issued by JTWC. && .Discussion... With the continuing influence of an ongoing monsoon pattern, episodes of scattered showers and isolated thunderstorms can still be expected this weekend and much of next week. Rainfall doesn't look as heavy as in the recent past, but with saturated soils in the Marianas, especially on Guam, any locally heavy showers could produce brief flooding. Both GFS and ECMWF show the possibility of a weak disturbance developing near the islands over the next couple of days, which could result in heavier rain than currently forecast, and we will closely monitor any developments in the area. && .Marine... The wind forecast is a little tricky after today, as gentle east to southeast winds are expected to become variable tonight, then pick up to gentle from the north to northeast Sunday as a weak disturbance develops just to the east. But in a light wind field, winds can change quickly from one model run to the next, so the situation will bear close watching, as noted above. Meanwhile, west swell generated by 93W/94W out west is expected to build the next couple of days, raising surf along west facing reefs, possibly to hazardous levels by Monday. && .Tropical Systems... The large monsoon depression that contains Invests 93W and 94W is quite a spectacle on satellite imagery, with a large area of strong convection associated with 94W at the northeast end of the elongated pressure pattern, and another large area of really intense convection associated with 93W at the southwest end, east-northeast of Mindanao in the Philippines. Monsoon gales are present under both convective areas, as shown on the ASCAT analysis. The two areas are separated by about 300 miles of thin cirrus clouds with no significant weather and much lighter winds. But a rapid satellite loop shows what appears to be a low-level circulation ejecting westward out into the open from 94W to near 17N 132E at 540 AM ChST, not too far from JTWC's 530 AM position for 94W of 17N 133E given in their TCFA. But this is well removed from either area of convection, and it is still far from clear how this complex monsoon system is going to develop. Some type of merger is expected, and both the ECMWF and GFS have 93W/94W consolidating into a big tropical storm by Sunday morning near 17N 128E. Meanwhile, 95W presents itself on satellite as a small area of convection on the northeastern flank of a small circulation south of Wake Island near 15N 166E. ECMWF and GFS both develop this into a tropical cyclone in the next day or so, and ship it out to the northwest into the open Pacific. && .Eastern Micronesia... From this morning's satelitte imagery, Pohnpei and Kosrae remain under a quiet ridging pattern. On either side of this fair weather regime, unsettled weather lurks on the sidelines. Well north of the main islands, Invest 95W is generating a broad region of active showers and thunderstorms. To the east, a trade-wind trough passing through Majuro is expected to lift to the northwest, trailing after 95W and effectively leaving the main islands under relatively quiet conditions for the forecast period, although, brief upticks in showers can still be expected from a couple of weak disturbances. Latest model guidance has this timing on Monday night and Wednesday night for Kosrae and Monday night for Majuro. Marine conditions consist of 3-5 foot combined seas and gentle to moderate winds until at least midweek. && .Western Micronesia... With the broad monsoon disturbance brewing to the north, Yap and Palau continue to be subject to a strong, surging west-southwest winds that are hazardous for small craft. A high surf advisory also remains in effect as seas build up to 8 to 11 feet today, before subsiding to below hazardous levels Sunday night or Monday. Wave model heights have gone down a foot compared to yesterday's model run, but this was not enough to change the schedule of this advisory since it was not enough to reach below hazardous levels. Latest ASCAT reveals a wind field of 15 to 25 kt reaching throughout Yap and Palau waters. Gusts have reached upwards of 30 kts according to the hourly observations at the Palau airport. Showers and thunderstorms have been relentless as well. As of 4 am this morning, WSO Palau recorded an impressive 5.82" of rain for the 24-hour period. In comparison, Yap received 0.78" during the same period. As the disturbance lifts northwestward, a brief break in showery conditions will occur before another monsoon pattern takes shape midweek. Chuuk has fallen within the boundaries of the drier regime in eastern Micronesia. Fair weather can be expected over the weekend and into next week. Marine conditions will also be uneventful with combined seas of 3 to 5 feet and gentle winds for the extent of the forecast period. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Middlebrooke Micronesia: Cruz