


Area Forecast Discussion
Issued by NWS Tiyan, Guam
Issued by NWS Tiyan, Guam
031 FXPQ50 PGUM 142006 AFDGUM Area Forecast Discussion National Weather Service Tiyan GU 606 AM ChST Wed Oct 15 2025 .Marianas Update... Invest 96W, just SW of Guam near 12N142E, continues to keep Guam and Rota locked in a wet pattern for at least another day. After a drier Tuesday evening and the first few hours after midnight, showers have steadily filled in across Guam`s waters with a significant drop off toward Rota. Invest 96W will continue WNW into the Philippine Sea tonight and Thursday, ushering in drier weather for the Marianas for late week. More interesting is an expansive westward-moving upper- level low southeast of Wake Island and the much drier mid- and upper-level conditions ahead of it. Latest ALPW shows a significant drop off in atmospheric moisture content above 700 mb with Blended TPW showing a dropoff in PWat from about 2.5in over the Marianas to about 1.5in between Pohnpei and Wake Island. Such trends point to the inevitable transition from wet season to dry season over the next couple of months. On the waters, little change was needed except to freshen short-term seas which will hover between 5 and 8 ft with the largest seas farther south. A long-period north swell from distant TY Nakri will keep surf elevated along north-facing reefs through the week. For Guam and Rota waters, winds will remain hazardous to small craft through tonight. && .Tropical Systems... Invest 96W, still without a discernible low-level circulation center is centered SW of Guam near 12N142E, based on mid-level rotation within the trough axis. This system is still favored by the vast majority of models to gradually become better organized out over the Philippine Sea as it continues west and out of the Guam AOR. Until then, its presence will continue to focus showers over the lower Marianas. Over Eastern Micronesia, an elongated circulation sits near Kosrae. Models maintain a weak circulation for another 12-24 hours before showing it opening into a surface trough as it continues westward toward Chuuk. && .Hydrology... A NW-SE band of heavy showers has steadily trained over Guam since about 330 AM this morning with automated gauge reports suggesting rainfall rates of 4-6in/hr. These heavy rains are largely focused over Guam and decrease significantly toward Rota. The nearby presence of 96W, just SW, will maintain a wet short-term outlook, for Guam and Rota, through tonight. Later on today, even short burst of torrential rainfall rates could be sufficient for flash flooding of streams due to increasingly saturated soils from the past several hours. Folks in steeper terrain areas should be alert to the possibility of mudslides. && .Eastern Micronesia Update... A disturbance continues to drift westward through Kosrae State with showers and thunderstorms having pushed to the south of Pohnpei and Kosrae. The disturbance, an elongated circulation oriented SW-NE, seems to be centered just north of Kosrae. An ENE-extending surface trough continues to lift WNW over the Marshalls with Majuro winds out of the S and Kwajalein winds turning SE. Have initially increased winds for Kosrae today, based on scatterometry indicating stronger winds near the disturbance. For areas E of the disturbance and S of the trough, winds will be light to gentle. Elsewhere, winds will be mostly moderate. Convection for both Kosrae and Majuro will taper off by Thursday, though in the meantime, could be marked by brief stronger gusts. A broad upper-level low just east of Wake Island seems just a bit too far north to significantly invigorate convection and convective gusts. Seas continue to be dominated by a solid N swell that will persist through the week. Seas will hover between 6 and 7 ft for most locations the next several days, though will edge closer to 8 ft just E of the Marshalls. && .Western Micronesia Update... A broad circulation sits near Palau and is helping to keep regional winds calm. Convection has steadily decreased around Palau and Yap so the latest forecast update reflects a drier short-term trend with a transition to increased showers for tonight. The passage of Invest 96W to the NE and N of Yap will be largely a non-event for both locations except for weakened winds that will shift S over the next couple of days and occasional upticks in showers and thunderstorms. Farther east at Chuuk, drier weather will give way to an increase in showers as a trough passes through the area today. A broader disturbance now near Kosrae will bring more moisture to Chuuk by late week. Seas will remain dominated by a long-period north swell with combined seas averaging between 4 and 5 ft, occasionally reaching nearer 6 ft at Chuuk. && .Prev discussion... /issued 1152 PM ChST Tue Oct 14 2025/ Marianas Update... After a fairly dry evening, showers have begun to redevelop near and just south of Guam-Rota. However, latest satellite and model trends have backed off on the widespread and heavy nature of the showers for overnight, thus have reduced intensities to moderate and the coverage to numerous (70 POPs). Showers will be fairly quick-moving with latest radar VAD-wind profile indicating 20-25 kt winds in the lower several thousand feet above ground. This will reduce the potential for significant rainfall accumulations. Eastern Micronesia... Latest incoming scatterometry data continue to show the disturbance trekking west, set to pass just north of Kosrae Wednesday. ASCAT wind data from 00Z Tue and the incoming 12Z data show pockets of fresh to strong winds in the southern periphery of this disturbance. As such, have updated the Kosrae forecast for tonight to freshen winds and resultant wind waves. Western Micronesia... Latest satellite trends show late-evening stabilization greatly reducing convective coverage across Palau and Yap. While the mid- morning forecast philosophy still leans toward increase showers around or soon after daybreak, have proceeded to update the forecasts for Yap and Palau tonight to reflect drier overnight conditions. Prev discussion... /issued 559 PM ChST Tue Oct 14 2025/ Marianas Synopsis... Moderate to fresh southeasterlies prevail across the region. Satellite imagery and Doppler radar indicate slow-moving but steady rows of showers moving into Rota waters. Buoys indicate seas are around 5 to 7 feet. Discussion... A generally unsettled pattern caused by nearby tropical disturbance Invest 96W embedded within an east-west oriented trough, is likely to produce heavy showers and thunderstorms to bring localized flash flooding risk to Guam and Rota for at least the next few days. Heavier showers and thunderstorms are expected to begin after midnight, to then peak in coverage and intensity Wednesday. As such, a Flash Flood Watch has been issued for Guam and Rota through late Wednesday night. Uncertainty remains high regarding wind potentials due to the lackluster nature of the synoptic regime involving Invest 96W, but at this time, breezy winds of 25 mph with gusts to 35 mph are possible Wednesday over Guam and Rota. Weather conditions are expected to be slightly better at Tinian and Saipan, while also dodging most of the more intense outflow boundaries produced by 96W. Invest 96W is expected to exit the region before the weekend, to then intensify in the open waters of the Philippine Sea as it heads towards Luzon during the weekend. This will allow conditions to improve considerably beginning Thursday, with a return to a drier regime expected toward the weekend across the Marianas. Marine... Fresh to strong southeasterlies, as well as increasing southeast wind waves, will produce conditions hazardous to small craft through at least late Wednesday night. As such, a Small Craft Advisory has been issued through late Wednesday night. Conditions are expected to steadily improve once Invest 96W moves away from the region to the west in the second half of the week. Combined seas of 6 to 8 feet near Guam and Rota, and 5 to 7 feet near Tinian and Saipan tonight, will taper down a few feet by Thursday, once wind waves decrease after Invest 96W`s passage. Hydrology... The most recent model guidance and satellite interpretation analysis indicates rainfall potential of 3 to 5 inches possible over Guam and Rota over the next 48 hours. If rains persist, soils may become saturated with any additional rain resulting in pure runoff, which may exacerbate flash flooding potential further into the week. Based on the most recent data, rainfall is expected to taper down significantly after 96W`s exit, resulting in lesser shower potential for the rest of the week. Tropical systems... A loosely organized tropical disturbance known as JTWC`s Invest 96W, has a center axis of momenta just near 11N146E well southeast of Guam. Moderate to occasionally deep convection is associated with this feature, mainly associated with the east-west oriented trough within which this disturbance is embedded in. Invest 96W is still rated LOW by JTWC, meaning development into a tropical cyclone is unlikely within 24 hours. While the system remains with no discernible center of rotation, a sharpening leading edge of the trough will be the vorticity center on which 96W will latch onto as it crossed the Marianas, deepening the convection as it exits to the west. This feature will then intensify in the open waters of the Philippine Sea as it heads towards Luzon during the weekend. For updated information on 96W, please refer to the Significant Tropical Weather Advisory, issued by the Joint Typhoon Warning Center, under WMO header ABPW10 PGTW. A trade-wind disturbance is centered near 4N162E just southwest of Kosrae. Moderate to deep convection is associated with this feature, producing numerous to widespread showers and isolated to scattered thunderstorms across a wide sector of eastern Micronesia from 160E to 170E, between 2N and 7N. This feature is expected to lose its center of rotation and bulk of convection overnight, dissipating into moreso a broad surface trade-wind trough that will continue to move along the trades over the next several days. Eastern Micronesia... A tropical disturbance is producing an low located near 4N162E (just southwest of Korea),and trough extending from the low to east of Majuro near 7N175E. The showers associated with this disturbance are numerous to widespread with isolated thunderstorms and covering most of the central region of eastern Micronesia. The heaviest showers are moving towards Kosrae. A call from WSO Pohnpei informed us that 0.77 inches had fallen by around 12:30 PM ChST. This disturbance is expected to arrive at Pohnpei around Thursday. Model guidance suggests, this disturbance will continue into western Micronesia as a trough over the weekend. Along the eastern boarder, the Intertropical Convergence Zone (ITCZ) is anticipated to build back in over the weekend bring more showers back to the region. Altimetry shows combined seas of 5 to 6 feet near Pohnpei and Kosrae, and 6 to 7 feet near Majuro. Both North Point and Utwe buoys confirm the heights near Pohnpei and Kosrae respectively. Winds are expected to be light to gentle over much of the region, with a caveat of moderate winds near heavier showers. There are two swells at play here, the north swell of about 4 to 6 feet coming from distant Tropical Nakri. The other swell is a southeast swell of about 3 feet. Surf along north facing reefs are expected to be elevated, however are expected to be below the 9 foot threshold for an high surf advisory. Western Micronesia... Scatterometer data shows a westward moving, elongated circulation centered east of Palau and south of Yap, near 6N137E. This circulation was part of of the area monitored as Invest 96W, but as discussed in previous discussions, this circulation was expected to remain elongated. More attention is now on the sharp trough heading towards the Marianas, which is where Invest 96W was relocated this morning, and is now centered near 11N146E. Scattered showers and isolated thunderstorms are still developing along the elongated center and are moving across Palau this evening and expected to move through Yap Proper later tonight. The potential for scattered showers and isolated thunderstorms will linger through Wednesday as the elongated circulation drifts off to the west, potentially opening back up into a trough. Depending on how Invest 96W develops as it moves west of the Marianas, gentle south to southwest flow may develop across Palau and Yap Wednesday through Thursday, before turning southeast to east late this week as a trough approaches the region, potentially prolonging scattered showers and periods of isolated thunderstorms across Palau and Yap into the weekend. For Chuuk, with Invest 96W moving closer to the Marianas, dry weather has moved across Chuuk Lagoon and is spreading westward. This drier weather will continue through tonight, but a broad trough with an embedded circulation near Kosrae will continue to drift westward. This will lead to showers starting to increase as early as Wednesday afternoon. However, models show the embedded circulation dissipating, with the vorticity moving north of Chuuk, this may keep showers on the low-end of coverage across Chuuk, with showers favored more along 10N later this week. Winds are expected to be easterly and mainly light to gentle, occasionally becoming moderate with the passage of troughs. Satellite altimetry shows seas around 4 to 5 feet across the region, mainly driven by the north to northeast swell. Surf along north facing reefs will remain elevated across Palau, Yap, and Chuuk this week, due to pulses of longer-period northerly swell moving through the region, but are expected to remain below hazardous levels of 9 feet. && .GUM WATCHES/WARNINGS/ADVISORIES... GU...Flood Watch through late tonight for GUZ001. MP...Flood Watch through late tonight for MPZ001. Marianas Waters...Small Craft Advisory until 6 AM ChST Thursday for PMZ151-152. && $$ Marianas/East and West Micronesia Update: Aydlett Marianas: Aydlett