Updated: 7:00 PM ChST on November 01, 2014
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Area forecast discussion...updated National Weather Service tiyan GU 615 PM chst Friday Nov 28 2014 Marianas synopsis... an area of scattered showers associated with an old and narrow shear line extends eastward from just east of Guam to near 13n152e. Upper-level divergence has been firing up a few thunderstorms along the shear line near and to the west of Guam. Next significant weather maker still appears to be a surface trough currently approaching Kosrae. && Discussion... GFS initializes shear line the best...bringing scattered showers to Guam overnight...then the boundary slides southwestward and Ushers in a drier air mass for the remainder of the weekend. Kept thunder in the forecast for Guam as favorable upper-level environment appears to be hanging around. Reduced cloud cover and probability of precipitation for Rota northward due to the narrowness of cloudiness associated with the shear line. Night shift will need to monitor the progress of the shear line to make sure mesoscale short term forecast adjustments are not needed. Models still remain bullish on the system currently approaching Kosrae...eventually tracking it south of Guam on Tuesday and Wednesday next week. For now...broad brushing the forecast via mostly cloudy/isolated shower wording Tuesday through Thursday should cover the time frame this system will be passing through. Once again...drier trades are expected to build back in for the end of next week. && Marine... latest model runs and satellite trends suggest low pressure approaching Japan will not be weakening the subtropical ridge quite as fast as earlier anticipated. Therefore...have extended the Small Craft Advisory for marianas waters until 5 PM Saturday afternoon. Otherwise...still expect seas to gradually subside early next week as north swell energy replaces trade-wind swell energy. At this time...still expect north swell heights to peak below heights necessary to generate high surf on respective exposures. If system currently approaching Kosrae does develop... small craft and high surf advisories will be possible once again by the middle of next week. && Updated to add micronesia discussion Eastern micronesia... convection associated with a surface trough affecting Majuro has moved westward and is now affecting Kosrae. This trough will affect Pohnpei with scattered showers and isolated thunderstorms Saturday and Saturday night. Models forecast this trough to develop into a circulation as it moves quickly towards the west. Somewhat drier conditions will build in over Majuro and Kosrae following the disturbance. However...models consistently depict a band of trade-wind convergence to set up across the region between 6n and 9n. This will bring wetter weather to Majuro and possibly Pohnpei early next week. High surf advisory remains in effect for east-facing reefs at Kosrae. Hazardous surf will persist at Kosrae through tonight. && Western micronesia... drier weather moved into Chuuk this morning after a round of showers and thunderstorms late Thursday night. Therefore...fresh northeast trades and only isolated showers are expected through Saturday. The disturbance over Kosrae tonight will bring scattered showers and isolated thunderstorms to Chuuk late Saturday and Sunday. Models spin this disturbance into a circulation...passing south of Chuuk Sunday morning. Convergence behind the circulation will maintain unsettled weather into early next week. For Yap and Palau...showers and thunderstorms are persisting near these locations this evening...but conditions are going to improve at Yap later tonight. A broad but weak circulation south of Yap and Koror will keep to the south as it heads west and maintain a broad area of low-level convergence focusing over Koror. Saturday and Sunday will be a little drier but still the overall pattern will be fairly unstable. GFS shows the circulation that develops from the trough now near Kosrae will progress westward and be near Yap on Wednesday. Will have to keep a close watch in the long-term to see how this evolves. && Gum watches/warnings/advisories... GU...none. Marianas waters...Small Craft Advisory until 5 PM chst Saturday for pmz151>154. && $$ McElroy/devita