Area Forecast Discussion

Marianas Update

Former Invest 93W will continue to open into a trough as it approaches the Marianas today. Shower coverage, as well as thunderstorm potential, will increase throughout the day today as the trough nears. High-end scattered showers and isolated thunderstorms are expected starting tonight and will continue through at least Tuesday night. Gentle to moderate east to northeast winds will prevail through midweek. Combined seas around 3 to 4 feet will increase a foot or so tonight before slowly diminishing around midweek. Locally choppy seas can be expected near any heavier showers and thunderstorms. A low risk of rip currents is expected to continue through at least today, but may rise to moderate along east- facing reefs starting on Tuesday as an east swell slightly builds in.

Tropical Systems Update

A tropical cyclone formation alert (TCFA) was continued early this morning by the Joint Typhoon Warning Center (JTWC) for Invest 92C as it nears the Date Line. This means that formation into a tropical depression is likely within the next 24 hours. The disturbance is expected to drift west to west-northwest over the next two days as it continues to strengthen, before turning more northwest around midweek. Residents of the northern Marshall Islands should monitor the forecast over the coming days as impacts from swells generated by Invest 92C are expected. Please see the Special Weather Statement for additional information. For more information on Invest 92C and the TCFA, see bulletins issued by JTWC under WMO headers ABPW10 PGTW and WTPN22 PGTW.

Invest 93W was closed by JTWC yesterday evening and the former invest is expected to continue to open up into trough as it nears the Marianas. Periods of high-end scattered showers, isolated thunderstorms, and moderate winds are possible tonight through at least Tuesday night across the Marianas.

Eastern Micronesia Update

Periods of scattered showers and isolated thunderstorms will continue through early this week with the highest rain chances being at Majuro on Tuesday. Light to moderate west winds are expected to prevail into midweek at all sites. Combined seas of 4 to 5 feet will persist through today with seas building starting on Tuesday as swell from Invest 92C starts to arrive. Please see the Special Weather Statement and the Tropical Systems section for additional details on the latest on Invest 92C.

Western Micronesia Update

Areas of scattered to numerous showers continue in the vicinity of the axis of the monsoon trough this morning with surface convergence noted in the vicinity of Palau and Chuuk. Shower coverage and thunderstorm chances will increase to numerous starting on Tuesday at Palau with locally heavy rainfall possible. Mostly scattered showers and isolated thunderstorms are expected through early this week at Yap. Surface convergence in the vicinity of the monsoon trough will keep numerous, locally heavy, showers and isolated thunderstorms possible at Chuuk through tonight. Gentle to moderate west winds will continue through early this week at Palau with gusts up to 25 knots possible. Gentle to moderate west winds will persist today at Chuuk before easing to mostly gentle tonight and into Tuesday. Light and variable winds are expected through midweek week at Yap as troughing passes to the north. Generally benign marine conditions are expected to continue across the region. Combined seas of 2 to 5 feet will persist into midweek, with the highest seas being at Chuuk.

Prev discussion

/issued 638 PM ChST Sun Jul 26 2026/

Marianas Synopsis... Light to gentle easterlies prevail across the region. Satellite imagery and Doppler radar indicate isolated showers sprinkled across the island chain. Buoys show seas are around 3 feet.

Discussion... 10 to 15 mph east winds will prevail across the region through Monday, to then shift to the northeast, as Invest 93W breaks down into an open trough and moves in. This will allow slightly higher shower and thunder coverage to develop, with scattered showers and isolated thunderstorms now expected Monday night through at least Tuesday night.

Marine... Combined seas of around 4 feet will pick up another foot beginning Monday night as east swell finally overtakes the westerly swells, to then diminish once again around midweek. A low risk of rip currents is expected along all reefs of the Marianas for much of this week.

Tropical Systems... Invest 92C from the Central Pacific Hurricane Center will be crossing the Date Line by tomorrow (Monday) morning. As it crosses the Date Line, it'll enter JTWC's (the Joint Typhoon Warning Center), and WFO (Weather Forecast Office) Guam's AOR (Areas of Responsibility) accordingly. This system shows improved organizational structure, and it would not be surprising at all to see JTWC issue a TCFA (Tropical Cyclone Formation Alert - meaning a tropical cyclone (Depression or stronger) development is likely within 24 hours.

The models have been really "fickle" with this system, going back and forth on when it's current due west track will turn northwesterly. 3 4 to 5 days ago, it was at 170E that it made the turn...for a couple days it was turning at 165E...now (and over the last 36 hours...it's back to 170-172E when it makes the turn. The problem here lies with some of WFO Guam's warning points, namely Utirik Atoll, and Wotje, Atoll (also Enewetak Atoll if it waited until 165E to make the NW turn), as a delayed westward turn will increase the northeast to northwest swell, with DESI showing swell heights of 5 to 7 feet possible at Utirik, dropping down into the 2 to 5 foot range from Enewetak, through Kwajalein, to Majuro. Given how flat these atolls are, any surge, especially from the west to northwest (typically, the leeward side of the atolls) would be increasingly susceptible to any swell-related inundation and/or coastal erosion.

Then, further west, we have Invest 93W (which continues to be rated at "Sub-Low"), which is located northeast of Chuuk/northwest of Pohnpei. Late this afternoon, the LLCC (Low-Level Circulation Center) was located near 12N156E, heading west. This disturbance has had an asymmetric history for the past few days, with most convection found on the southern through western flank of the system, as it was fighting easterly 20-25kt flow at 200mb (per the GFS). Recent analysis showing some shallow convective attempts starting to occur on the northern through eastern portions of the circulation. The analysis also shows shear has become slightly less hostile, estimated at 15 to 20 knots from the east. Overall, 93W is expected to remain on a westerly track, eventually bringing increased rainfall potential to the southern half of the Marianas over the next few days, mainly from Guam north to Saipan.

Eastern Micronesia... The main focus was on swell heights/potential for Majuro and surrounding locations in the northern FSM/RMI, with a coordination call held with WSO (Weather Service Office) Majuro earlier this afternoon. As such, given Invest 92C's continued organizational improvement today, and after coordinating with JTWC regarding their posture/forecast input, WFO Guam hoisted a Special weather Statement for Utirik, as this atoll will be the closest to whatever develops from 92C. A social media graphic was also posted to cover a "broader range" of atolls after some internal collaboration. Otherwise, the remainder of the forecast was in good shape with just minor changes/updates needed.

For mariners, gentle to moderate winds at Pohnpei and Kosrae (mainly tied to convective gusts and the monsoon flow) remain possible from time to time. Overall, winds will be light to gentle for the majority of the forecast period. Seas in the 3 to 5 foot range may increase a foot or two for the latter half of the week (maybe a little sooner), depending how Invest 92C evolves over the next few days.

Western Micronesia... An unsettled weather pattern continues across the region. Latest Himawari visible satellite imagery shows a band of scattered to numerous locally heavy showers and isolated thunderstorms just west to northwest of Palau associated with strong surface convergence, and scattered showers to the northeast near Yap associated with a weak circulation nearby, embedded within the monsoon trough. The monsoon trough is anchored just north of the region, extending south- southeast across the Philippine Sea to the weak circulation just northeast of Yap, then curving eastward to pass just north of Chuuk, before extending east-northeast into Invest 93W. The monsoon trough will flex slightly northward throughout the week and maintain a wet southwesterly to westerly monsoon pattern across Palau and Yap. Surface observations at Koror have reported wind gusts to 25 kt throughout the afternoon with passing showers, and gusts have been included in the forecast accordingly, mainly with heavier showers.

Latest model and satellite trends point to showers continuing overnight and through the next few days as the circulation near Yap passes north of Palau and winds shift toward the southwest, maintaining convergence across the area. Showers will become numerous and locally heavy at times for Palau, and latest guidance indicates this around Tuesday and Tuesday night. Yap will see scattered showers through much of the week, which look to increase toward the end of the week as the monsoon trough, and convergent westerlies, shift farther north. For Chuuk, numerous showers and isolated thunderstorms diminished this afternoon as convergence between the monsoon southwesterlies, and cross-equatorial southerlies shifted away. Scattered showers will continue overnight and become numerous Monday as Invest 93W passes to the north of Weno. Showers diminish toward the end of the week as the monsoon trough, and associated disturbances, shift farther north of the region.

Benign marine conditions continue. Altimetry and Yap buoy data depict combined seas between 2 and 4 feet near Palau and Yap, and 3 to 5 feet for Chuuk, comprised of broad west to southwest swell, and secondary light easterly swell. Seas and swells look to increase toward the end of the week, associated with a strengthening disturbance far to the north, but magnitude and timing of this increase remain uncertain this far out.

GUM WATCHES / WARNINGS / ADVISORIES

GU...None. MP...None. Marianas Waters...None.