Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
091 FXPQ50 PGUM 132021 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 621 AM ChST Fri Jun 14 2024 .Marianas Synopsis... Satellite imagery is showing partly cloudy skies with isolated showers over Tinian and Saipan, with mostly cloudy skies and scattered showers for Guam and Rota. Lightning has been observed over the southern coastal waters. Latest altimetry and Ritidian buoy are showing combined seas of 3 to 5 feet. && .Discussion... Deeper layer moisture, as noted by the CIMMS MIMIC precipitable water values and model time heights, along with passing weak trade troughs, will result in rounds of scattered showers through Saturday night. The best potential for scattered coverage will be during the evening hours through around 9 AM, as has been the trend over the past few days. In addition, an approaching Tropical Upper- Tropospheric Trough (TUTT) cell to the northeast of the Marianas is approaching. As the TUTT cell moves over and west of the Marianas, upper-level divergence will help promote the development of thunderstorms through Saturday night as well. By Sunday, convection looks to diminish as the surface and upper-level features both look to push far enough west away from the Marianas. Expect generally isolated showers next week, although some model guidance is suggesting moisture and disturbances creeping north out of Micronesia and possible bringing an uptick in showers at times, especially for Rota and Guam. && .Marine/Surf... Gentle to moderate trades will prevail into the weekend. Combined seas build to 4 to 6 feet today will slowly increase to between 5 and 7 feet over the weekend as trade swell strengthens. Weak trade-wind troughs along with a TUTT cell to the northeast of the waters are expected to bring rounds of scattered showers and a few thunderstorms to the waters through Saturday night. Occasional strong gusts are possible with the thunderstorms. A moderate risk of rip currents is expected to continue along east facing reefs and expected to remain low along all other reefs through Saturday. Surf could increase about a foot beginning Saturday night as the trade swell strengthens. This could bring a moderate risk of rip currents to north facing reefs. && .Eastern Micronesia and Chuuk... An Inter-Tropical Convergence Zone (ITCZ) stretches across most of the region, extending from the Marshall Islands to eastern Chuuk State, mostly between 5N and 11N. No major changes were made to the forecast. Scattered to numerous showers are expected through at least the weekend and maintained the convectively-driven gusts winds that the GFS has for Kosrae tonight, reaching up to 30 mph near heavier cores. By Monday, the ITCZ is expected to fragment into a series of troughs, keeping periods of scattered showers and isolated thunderstorms through most of next week. Altimetry shows combined seas across the region are around 3 to 5 feet, and model guidance depicts seas up to 6 feet east of the Marshall Islands. Scatterometry shows gentle to moderate winds along and south ITCZ, with moderate to fresh winds north of the axis and embedded within heavier convection. Models continue to indicate winds will generally be gentle to moderate for the region, with GFS showing occasionally strong gusts with heavier showers within Kosrae waters tonight. Trade swell slightly subsides, decreasing seas by a foot this weekend. && .Western Micronesia for Palau and Yap... Satellite imagery shows clusters of showers and thunderstorms developing in far western Micronesia this morning. Within the light and variable wind field, there is a weak trough that drapes across Palau and extends into eastern Yap State, as well as another trough and trade-convergence affecting Yap Proper. Model guidance suggests that shower coverage will shuffle around throughout the day, with convection re-organizing near and west of Yap for the first part of the day, then quickly pushing off and dissipating to the west of the islands late afternoon for Yap and tonight for Palau. Additionally, as the TUTT cell northeast of the Marianas and an attendant trough extending to the southwest, continue to drift westward, the risk for thunderstorms is expected to persist across Palau and Yap through at least Saturday night. Afterwards, models show the TUTT lifting northward which would help to decrease the potential for thunderstorms on Sunday. However, an overall wet pattern is expected for Palau and Yap, supported by troughs and trade convergence that break off from the ITCZ and push westward into Palau and Yap through at least early next week, along with some strengthening of the trade winds around both locations. Buoy and altimetry data show seas around 2 to 3 feet and scatterometry data indicates light to gentle winds. Marine conditions are not expected to change that much over the next several days, except for a slight increase in trade swell that would bump seas up to 4 feet around Yap next week. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...None. MP...None. Marianas Waters...None. && $$ Marianas: Slagle Micronesia: Cruz