Flash Flood Warning: Flooding imminent on Oahu

HONOLULU—At 8:23 p.m. on Tuesday, April 6, the National Weather Service issued a Flash Flood Warning for Oahu through 11:15 p.m. A Flash Flood Warning means flash flooding is imminent or occurring in streams, roads, and low lying areas. The National Weather Service says to move to higher ground now and to not cross fast flowing or rising water in your vehicle or on foot.

Runoff from the storm may also cause rock and mudslides in steep terrain.

At 8:15 p.m., radar showed extremely heavy rain along the Koolau Mountains that was spreading westward to communities in central and northern Oahu. The National Weather Service reports that this is evolving into a dangerous situation as torrential rain over the Koolaus continues to redevelop in the same areas. Other locations in the warning include, but are not limited to, Punaluu, Waiahole, Hauula, Kailua, Kaneohe, Waimanalo, Mililani, and Wahiawa.

Flash floods occur during extended rainfall events or within a few hours after the rainfall, according to the Pacific Disaster Center. Generally, if rainfall is of long enough duration, it will eventually cause flooding along the rivers, creeks, and streams draining the catchment area where the rain is being collected. But if the intensity of the rain—the number of inches of rain falling in a given time frame—is too great for the stream system, including flood plains, to carry the water away, flash flooding occurs.

The words “watch” and “warning” are used for two different levels of flood alerts. A flash flood watch or flood watch means that flooding or flash flood is possible in the area. The basic message of a flood watch is exactly what it sounds like: “Watch closely, conditions suggest a high likelihood of flooding.” When the word “watch” is replaced by the word “warning,” flooding or flash flooding is imminent or already beginning to occur. If you are in a low-lying or flood-prone area, act immediately to ensure the safety of your family. When a warning is issued, it is too late to prepare property to withstand flooding. You may have only seconds to act.

The National Weather Service says that this warning may need to be extended beyond 11:15 p.m. if flash flooding persists.

For more information, visit the National Weather Service website.