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Area forecast discussion National Weather Service tiyan GU 754 am chst Thursday Jul 30 2015 Synopsis... pgua Doppler weather radar shows isolated showers moving through the marianas waters. A tropical disturbance about 1160 miles east of Guam is slowly moving west and could affect the marianas early next week. The VAD wind profile reveals mainly south winds of 3 to 7 knots through the lowest 3 thousand feet of the air. && Discussion... movement and development of the tropical disturbance near enewetak was the main forecast problem early this morning. Gfs40 has moved closer to European model (ecmwf)-hires and navgem of yesterday. Meanwhile...ECMWF-hires and navgem remained fairly consistent. UKMET is a little south of them actually. Therefore...biased the winds in the grids toward the ECMWF-hires. Used the directions straight out of the model...just capped the winds at 21 knots for now until we know more. That gets US through Sunday night... Based on monsoon trough getting involved with the disturbance and lifting northward...extended the mostly cloudy through the end of the grids. Also added scattered showers near the end of the period and changed some temperatures to work toward consistency with what those conditions should allow. Model quantitative precipitation forecast estimates are 2.5 inches to 6 inches so went ahead and issued a bare-bones hydrologic outlook for signicant widespread rainfall next week. At the moment this is just an outlook...it may happen or it may not. && Tropical systems... the disturbance near enewetak is continuing to develop slowly. It is now the subject of a tropical cyclone formation alert from the Joint Typhoon Warning Center. It is moving mainly west...perhaps just a little to the north of west. It is expected to continue moving in the general direction of the marianas and will most likely arrive in the Sunday to Monday time frame. && Eastern micronesia... weather across the region from Chuuk to Majuro has come into a lull this morning. Heaviest weather is seen south of Chuuk and Majuro...and northeast of Pohnpei...near the developing tropical disturbance. This disturbance will continue towards the west or west-northwest...keeping north of the micronesia islands. A second circulation south of Majuro will work to anchor the monsoon trough in place...thus maintaining the moist monsoon flow across Chuuk...Pohnpei and Kosrae a few more days. The monsoon trough and 2nd circulation will shift west by next week allowing for some calmer weather to build in from east of Majuro. In the short-term...the forecast is based on all locations remaining convection-free this morning...but with weather firing up again near each this afternoon in a diurnal pattern. GFS maintains a fairly wet pattern at Chuuk...Pohnpei and Kosrae at least through Friday night. Will have to watch this closely...as well as a cluster of convection brewing just south of Majuro this morning near the circulation there. If this convection builds northward today...forecast there will need an update for more showers. Wave watch model continues to show a 3 to 4 foot southern hemisphere swell from the southeast to south-southeast arriving on Pohnpei and Kosrae. Swell will persist a couple more days. Surf is expected to remain below advisory levels. Surf will build on west-facing reefs for these locations and Chuuk today and Friday. && Western micronesia... Chuuk discussion is included above with eastern micronesia due to a similar synoptic pattern. The moist monsoon surge will continue across Palau...but keep just south of Yap for today. Infrared satellite shows scattered showers over Koror and to the east and west this morning. This weather has remained just south of Yap through the night. GFS keeps these showers just south the next couple days...but satellite trends suggest some northward shift...thus added more clouds and a slight chance of thunderstorms at Yap for tonight through Saturday. While the monsoon trough will remain in the vicinity the next few days...significant weather is not expected through the weekend. && Gum watches/warnings/advisories... GU...none. Marianas waters...none. && $$ Stanko/M. Aydlett