Hydrologic Outlook

ESFGUM This Hydrologic Outlook is for the Guam, Rota, Tinian and Saipan. A tropical disturbance, Joint Typhoon Warning Center's Invest 99W, is centered east-southeast of Guam near 10.6N 152.8E. This system remains disorganized, but is expected to move towards the Marianas late this weekend into next week. Model guidance shows 99W slowing down greatly on approach to the Marianas, leading to a prolonged heavy rain event. 99W is expected to bring heavy rainfall to Marianas from Sunday night through at least Thursday night, with two peaks between Sunday night through Monday night and Wednesday through Thursday night. Models differ significantly on the location and strength of 99W as it moves near the Marianas, however, there is strong agreement that heavy rainfall is likely late this weekend and into next week. There is potential for Guam and the CNMI to see rainfall amounts of 3 to 7 inches from Sunday night through Thursday night, though locally higher amounts will be possible. This rainfall is expected to produce minor flooding across the islands, with flash flooding possible in areas of heavier rainfall, especially over Guam. Residents in the Marianas need to closely monitor this developing situation as watches, advisories, and warnings could be issued later. If living near streams and rivers, prepare to move items away from stream and river banks. Make sure storm drains nearby are not clogged, especially if living in low-lying areas.