902 fxpq60 pgum 210938 afdpq Area forecast discussion National Weather Service tiyan GU 400 PM chst Sat Nov 21 2009 Synopsis... am sounding showed marked low-level drying...with a precipitable water of 1.21 inches. Jtwc invest area 94w is centered southwest of Chuuk near 4n147e and continues to spin up. Animated visible satellite imagery shows well defined low-level cloud lines feeding into 94w. Water vapor satellite imagery and GFS initial 200 mb wind and divergence fields show strong upper-level divergence over 94w. Northernmost spiral band from 94w comes to within 250 miles of Guam. && Discussion... no changes to forecast reasoning. 94w invest does appear to be The Elephant in the room and models remain in general agreement in developing 94w into a tc...then steer it in the general direction of the forecast zones. Inherited forecast brings 94w through during the Wednesday night/Thursday am time frame. Timing of scattered probability of precipitation for Wednesday and Thursday still looks good. Will maintain theme of broad brushing the wind fields until the development and movement of 94w becomes clearer. Late in the forecast period ridging builds back in from the southeast. Both the GFS and European model (ecmwf) hint at additional tc development in the monsoon trough to the southeast of the forecast zones...but way too early to nail anything down on such a forecast scenario. An spspq will almost certainly be needed for 94w during the next day or so. && Marine/surf... 12.5 km Quikscat shows sustained winds over the marine zones right at the 22 knots threshold. Observation from handars and metars have not been as impressive...but confidence still remains high that winds will freshen in response to high pressure building to the north of the marianas. A Small Craft Advisory for both winds and seas still looks likely for Sunday and Sunday night as winds increase to 20-25 knots and seas reach or exceed 10 feet. However...trade surge looks just weak enough to allow surf to peak just below advisory levels on north and east facing reefs during the same time frame. Nevertheless...will need to watch ipan buoy closely tonight and Sunday. && Eastern micronesia... a monsoon trough is persisting across the entire region with two small circulations embedded near kwajalein and northeast of Majuro. Convergence along the trough axis is expected to keep unstable conditions over Pohnpei through Monday night. Since Kosrae is farther south of the trough axis...weaker convergence should lead to less shower coverage through Sunday night. Located between the two circulations...Majuro is within the dissolved tail of the monsoon trough. As a result...isolated showers will prevail through the rest of the weekend with high-level clouds streaming across from convection near kwajalein. For early next week...tropical disturbance 94w near Chuuk will play a major role on the weather over eastern micronesia. If it develops into a tropical cyclone as most models have suggested...it will disrupt the monsoon trough and create a southeasterly inflow toward the cyclone itself. It can send a moderate southwest swell into Pohnpei. However this can actually bring a period of relatively fair conditions for the area before trade-wind convergence sets in around midweek. && Western micronesia... tropical disturbance 94w just southwest of Chuuk will likely keep inclement weather over Chuuk state through Sunday night. As it moves northwestward and strengthens early next week....converging southeast winds to the east of 94w are anticipated to prolong wetness over the area. Depending on the status of 94w...a southwest swell might create high surf scenario along south and west shores as well. By midweek...94w will be farther northwest of the state so that decreasing convergence should bring gradual improvement. Frequent showers and possible thunderstorms will accompany Palau into early next week as the monsoon trough remains in the vicinity. Drier northeast trade winds north of the monsoon trough are going to prevent these showers from spreading over Yap for another 24 to 36 hours. Afterward...aforementioned 94w will begin to lift the monsoon trough northward toward Yap with increasing shower coverage. Strong middle to upper-level subsidence related to a ridge of high pressure just northeast of the marianas should steer 94w northwestward passing between Yap and Guam around midweek. Since it is still too early to determine the future track of 94w at this point...have only introduced cloudiness and higher winds in the forecast. Residents in both Yap state and the Republic of Palau need to monitor 94w closely for the next several days. After midweek...both 94w and the monsoon trough axis will be north of both locations but west winds are expected to maintain some showers around. Now through Sunday evening... the combination of trade-wind swells and wind waves will keep sea heights around 7 to 8 feet. On Monday...94w can begin to increase northeast swells and develop a high surf event along North Shores of Palau and Yap. && Gum watches/warnings/advisories... GU...none. Marianas waters...none. && $$ McElroy/chan