SAIPAN – The U.S. National Weather Service in Guam is tracking a tropical disturbance, Invest 99W, that is slowly developing over western Yap State as it drifts west-northwest, the agency said in a bulletin issued at 9:17 p.m. ChST Sunday.
The system is currently rated sub-low by the Joint Typhoon Warning Center, meaning it is not expected to develop into a tropical cyclone within the next two days, NWS Guam said. Even so, 99W is already producing heavy rainfall and gusty winds across portions of Yap State, including Yap Proper.
The forecast points to a second-half-of-the-week threat for the western Caroline Islands. As 99W develops, monsoonal winds to the south will begin to intensify, the agency said, and a monsoon surge will be possible later this week with potential impacts to Yap and Palau. Heavy rainfall, gusty winds, and seas hazardous to small craft will all be possible across Palau and Yap Proper toward the latter half of the week. Uncertainty remains high for direct impacts from an organized tropical system, NWS Guam said.
For the Marianas, the potential for direct impacts from Invest 99W is very low, the agency said. But impacts from the broader monsoon pattern interacting with 99W will be possible this week. Uncertainty remains on how far east the stronger southerly flow will set up, but heavy rainfall with moderate to fresh southeast winds will be possible. Current guidance favors Guam for the heaviest rainfall, with decreasing rainfall amounts further north.
