Update: Flash Flood Watch, High Surf Advisory continues through Tuesday morning
HONOLULU—Heavy showers caused by the very moist air mass over the islands continues to pose a risk for flash flooding. The National Weather Service in Honolulu extended a Flash Flood Watch for all islands through 6:00 a.m. on Tuesday, December 21.
The National Weather Service advises Hawaii residents to monitor for later forecasts and be prepared to take action should Flash Food Warnings be issued. A Flash Flood Warning means flash flooding is imminent or occurring in streams, roads, and low lying areas and people in the storm’s path should move to higher ground now.
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.
Do not cross fast flowing or rising water in your vehicle or on foot.
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.
A High Surf Advisory has also been issued for North and East facing shores of Niihau, Kauai, Oahu, Molokai, Maui, and Hawaii Island. The advisory is also in effect until 6:00 a.m. on Tuesday, December 21. Surf along north facing shores will be 12 to 15 feet tonight. Surf along east facing shores exposed to the north swell will be 8 to 12 feet. Inexperienced swimmers should avoid entering the water along the north and east facing shores as the swell will produce strong rip currents that can overpower even strong swimmers.
A High Surf Advisory means that large breaking waves will affect beaches in the area, produce rip currents, and localized beach erosion.