Updated: 7:00 PM ChST on November 01, 2014
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Area forecast discussion...resent National Weather Service tiyan GU 731 am chst Friday Feb 27 2015 Resent for posting on webpage Synopsis...east trade-winds and a few small showers prevail across the marianas this morning. Relatively dry weather is expected through the weekend. && Discussion... little change made to the forecast. High pressure centered east of Japan will keep winds between 15 to 20 miles per hour today. 2 kft winds on the VAD were 25 knots and scatterometer data showed northeast winds between 15 to 20 kts. These wind speeds are consistent with current model predictions. Winds will decrease slightly tonight before another high pressure area builds out into the northwest Pacific and elevates wind speeds. Radar imagery this morning showed only a few small showers moving across the local area. Model predictions keep deep layer moisture lacking through the forecast. GFS...European model (ecmwf) and navgem show weak convergence across the area Saturday and they also portray a weak trough moving across the marianas Monday through Tuesday. While these features may produce a few more clouds still only expect isolated showers to prevail because of the lack of deep moisture. && Marine... observations this morning from the ritidian and ipan buoy indicated seas at around 7 to 8 feet. A north and a northeast swell will persist through the forecast. Global wave watch and ep10 show the north swell decreasing slightly Saturday night. These swells will keep a moderate risk of rip currents on north and east facing reefs. && Fire weather... a red flag warning remains in effect. Winds should increase during the day and relative humidity should decrease enough to satisfy red flag warning criteria. Dry conditions should persist at least through the weekend...so the Fire Weather Watch will most likely need to be extended. && Eastern micronesia... a shear line is expected to persist near Chuuk and Pohnpei...and north of Kosrae and Majuro through this evening. Two trade-wind disturbances moving westward from west of Kosrae will continue to interact with the shear line and trigger sporadic convection near Pohnpei today and Chuuk through this evening. As the sub-tropical high currently west of midway gradually weakens and drifts eastward on Saturday....this should cause the shear line to become more diffuse. Therefore anticipate shower coverage to decrease near both locations by Saturday morning. Latest rapidscat satellite imagery reveals a circulation lingering southwest of Pohnpei near 1n154e. Moderate to fresh trade winds generated by the aforementioned sub-tropical high are converging against gentle trades east of the circulation. This has established a convergent zone between the Equator and 5n from 161e to 173e. Deep convection associated with this zone will impact Kosrae through this weekend. As these trades push farther westward on Sunday... this convergent zone might extend into Pohnpei and Chuuk as well. Toward midweek next week...decreasing trade convergence should finally allow drier weather to return to all three locales. Since Majuro will be well to the northeast of the convergent zone...a dry trade regime will dominate the atoll most of the forecast period. The only exception will be Sunday and Monday which a weak trade disturbance from upstream east of the date line near 170w might spark off a few showers. Wave watch 3 model and satellite altimetry data are beginning to show a downward trend on the north-northeast swell across Chuuk... Pohnpei and Kosrae states this morning. This should allow surf to drop below hazardous levels on Kosrae by this evening and Pohnpei ..Chuuk on Saturday. Combined seas of 8 to 10 feet...hazardous for small craft operation will linger near Chuuk and Pohnpei until this evening. The north-northeast swell is expected to peak near Majuro today....producing surf heights of 8 to 9 feet. This will cause higher risk of rip currents but no hazardous surf is anticipated. && Western micronesia... the Chuuk forecast discussion is included with eastern micronesia above due to a similar synoptic weather pattern as Pohnpei and Kosrae. According to the latest water vapor satellite loop...the upper-level trough moving toward Yap and Koror from the southeast has weakened overnight. As a result...no significant weather is going to occur during the passage of this system...maybe a slight chance of thunderstorms near Koror tonight. Mainly moderate northeasterly trades and isolated showers will prevail through this weekend. A developing frontal system over southern China is going to track east- northeastward into southern Japan by early next week. This system should weaken the sub-tropical ridge near 22n which might allow the near-equatorial trough currently near 5n to lift northward closer to Koror and Yap. If so...the chance of showers will increase for both places by Monday. Satellite altimetry data from late last night indicate seas have drop further to between 5 and 7 feet near Yap. This agrees with the wave watch 3 model guidance which suggests surf has fallen below advisory levels this morning. && Gum watches/warnings/advisories... GU...red flag warning until 6 PM chst this evening for guz001. Marianas waters...none. && $$ Ziobro/chan