PGUM issues Area Forecast Discussion (AFD) valid 2019-11-21T08:47:00Z 831 FXPQ50 PGUM 210847 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 647 PM ChST Thu Nov 21 2019 .Marianas Synopsis...Radar and satellite shows only very isolated showers in the vicinity with mostly fair skies. Scatterometer shows some offshore winds of 15 to 20kt, slightly higher up north near Saipan. A couple of trade winds showers are seen approaching in the imagery with the one near 150E showing some lightning strikes and should arrive in the area later tonight or early in the morning. && .Discussion...Did little to change the previous forecast as models are mostly consistent with their previous forecast and the differences remain similar, as well. GFS just wants to blow-up a disturbance just south of Guam next Wednesday, or so, from what seems a weak circulation in the Marshalls. ECMWF, UKMET and ICON (consensus) NWP models are much less aggressive, but in basic agreement with enhanced trades for the next week. Since the trade winds are already elevated from the ongoing weather pattern in the western North Pacific, any additional pressure gradient from even a weak disturbance to our south will certainly enhance our winds in the Marianas. For now we are topping off at 25kt, sustained,...which does imply the possibility of some offshore gale force winds, especially in showers, by mid week. Precip forecast is not heavy until mid week with the influence of the disturbance south of the Marianas and any resulting trough that passes through us. See the Special weather statement issued earlier by the NWS WFO Guam as a precaution for enhanced winds and seas during the upcoming week. && .Marine...Similar discussion for resulting seas and surf from the enhanced winds mentioned above. For now, kept the seas down to 11 feet or so to match with the 25kt sustained winds...plus the resulting easterly swell. Yes, waves could be higher if we get that GFS-disturbance related system just to our south...but really need to wait on this. The GFS (the WW3 waves follows the GFS winds) has done this before, and I'd like see a better agreement between the European models. So far, there is an agreement that winds and seas will come up this coming week. Because of the 12 ft high surf criteria for high surf on the east facing reefs, looks like the 9 ft criteria for HIGH risk of rip currents will trigger first by about 12-18 hours. In addition, winds are a little stronger to the north, so the winds and seas build up will work its way north to south starting sometime during the day tomorrow (Friday). && .Eastern Micronesia, including Chuuk... Visible satellite shows fair weather in place at Chuuk, Pohnpei and Kosrae this afternoon while showers and thunderstorms are found near and east of Majuro. An east-west oriented surface trough sits south of all the main islands along 3N to 4N, and ends at a weak circulation near Majuro at 4N174E. Little change is expected the next few days with relatively fair weather continuing at Chuuk, Pohnpei and Kosrae...and a showery pattern persisting at Majuro through the weekend. The circulation near Majuro will slowly head west, passing near or just north of Kosrae, Pohnpei and Chuuk. Current forecast scenario keeps much of the showers north of these locations and where the trade-wind convergence to the north is greatest. Fresh to strong trades are expected through much of the forecast period across the region and more so to the north. 00Z ASCAT analysis shows strong trades along 15N east of 160E. GFS and NAVGEM both show development with the circulation as it heads west, but timing and intensity varies. Therefore, forecast confidence beyond day 3 is low and some changes can be expected the next few days as things evolve in the region. Fresh to strong trade winds north of the region will generate large swells capable of producing hazardous surf at Pohnpei and Chuuk the next few days. Northeast swell will build further early next week, possible bringing hazardous seas and surf to much of the region. && .Western Micronesia... Fair weather with partly cloudy skies, isolate showers and moderate trades is present at Yap and Koror this afternoon. The previously mentioned surface trough remains nearby, now just south of Koror, extending eastward to connect with the one mentioned, above. Showers and thunderstorms just north of the axis are present southeast of Yap. Little change is expected the next few days, but a weak trade-wind surge will bring fresh trades and a better chance of showers late Friday and Saturday to Yap, and to Koror on Saturday and Sunday. Seas and surf will rise in response to the stronger winds across the region this weekend. Seas and surf could become hazardous by Sunday. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. Marianas Waters...None. && $$ Edson/M. Aydlett