Guam, Northern Mariana Islands Coastal Flood Watch | Effective 04/12/2026 11:38

* WHAT...For the High Surf Warning, dangerously large breaking waves of 10 to 15 feet for Guam and 15 to 25 ft for Rota, Tinian and Saipan. For the Coastal Flood Watch, significant coastal flooding 1 to 3 ft for Guam, and 3 to 7 ft for Rota, Tinian, and Saipan are possible. * WHERE...North, east and south facing reefs of the Marianas. For the Coastal Flood Watch, north, east, and south facing shorelines. * WHEN...For the High Surf Warning, until 6 PM ChST Thursday. For the Coastal Flood Watch, from 6 AM ChST Monday through Wednesday afternoon. * IMPACTS...Numerous roads may be closed. Low lying property including homes, businesses, and some critical infrastructure may be inundated. Some shoreline erosion may occur. Breaking waves can sweep people off jetties and docks, and into dangerous seas. Life-threatening swimming conditions and significant beach erosion can be expected. * ADDITIONAL DETAILS...As STY Sinlaku moves towards the Marianas swell and surf are expected to rapidly build. This will generate dangerous surf and increase the risk for coastal inundation, especially as STY Sinlaku begins to move through the Marianas on Tuesday.