22/09/2026
Valid on Tuesday, September 22, 2026 at 5:20 PM ChST
…Invest 91W under a Tropical Cyclone Formation Alert…
Invest 91W is located near 12.5N 141.9E this afternoon, west of Guam. It is heading northwest away from the region and into the Philippine Sea. A Tropical Cyclone Formation Alert means this system is expected to develop into a tropical cyclone within the next 24 hours. With the current heading, no direct impacts are expected to the Marianas, Yap, and Palau, although monsoonal and trade-wind inflow are expected.
For the Marianas, scattered showers and isolated thunderstorms are expected. Winds are generally expected to be light and variable, that will build to 10 to 15 mph with gusts to 25 mph near heavier showers. These wet conditions are expected to linger through Wednesday for the islands and about a day longer for the marine. For the marine zones, this system is expected to produce a west-southwesterly swell once it strengthens, however at this time this swell is below a foot. Conditions over the Marianas are expected to improve Thursday.
The monsoonal inflow into 91W will continue to bring numerous to widespread, locally heavy, showers and isolated thunderstorms across portions of Yap State and Palau through Wednesday. Increased winds and occasional gusts up to 30 mph will be possible, especially near heavier showers and thunderstorms. Model guidance suggests that 1 to 3 inches of rain per day will be possible through Wednesday, especially for Yap. Be aware of the latest weather conditions and trends before traveling between islands.
For more information, please visit www.weather.gov/gum. For more information on Invest 90W, please visit https://www.metoc.navy.mil/jtwc/jtwc.html.
