Hawaii Braces for Severe Weather—Flash Flooding, Thunderstorms and Dangerous Lightning

Hawaii is under a flash flood watch until tomorrow afternoon as a low pressure system moves eastward towards the group of islands.

According to the National Weather Service (NWS), all the islands could be impacted by flash flooding—Kahoolawe, Kauai, Lanai, Maui, Molokai, Niihau, Oahu and the Big Island—due to heavy rainfall. Kauai and Oahu are thought to be at the greatest risk from flooding with heavy rain likely to affect urban and leeward locations as well as lower elevations, which are more vulnerable to flooding impacts.

A Special Marine Warning has also been issued for Kauai Channel, Kauai Leeward Waters, Kauai Northwest Waters and Kauai Windward Waters until 7:30 a.m. HST due to strong thunderstorms and wind gusts of 34 knots or greater. Boaters should seek safe harbor immediately until this storm passes—NWS advises that high waves, dangerous lightning, and heavy rain are possible with this storm.

A "Flash Flood Watch" means that conditions are favorable for flash flooding, which is life-threatening. According to NWS, people should avoid crossing flowing water in their vehicles or on foot.

An urgent marine weather message has also been broadcast by NWS for a small craft advisory in the Hawaii area. In effect until 6:00 p.m. HST tomorrow, NWS warns that seas of 5-8 feet will build to 8-12 feet by tonight, with southeast to south winds reaching between 15 to 30 knots. This advisory applies to the majority of Hawaiian waters and are hazardous to small craft. Inexperienced mariners—especially those operating smaller vessels—should avoid navigating in these conditions.

NOAA Hawaii Forecast
Issued at 5:15 a.m. HST, March 16, 2020, for 8:00 a.m. HST by NOAA. NOAA

How to Stay Safe During Flash Flood?

According to NWS, flash flooding is a quick surge in water levels, generally developing within six hours of the immediate cause—heavy rain, ice or debris jams and levee or dam failures. In some cases, flooding may even occur well away from where heavy rain initially fell—this is especially common in the western U.S.

Urban areas are especially prone to flash floods due to the large amounts of concrete and asphalt surfaces that do not allow water to penetrate into the soil easily, says NWS. Steep, hilly, or mountainous terrain produces rapid runoff and quick stream response.

Prior to any flooding, the NWS advises taking the following steps:

  • Create a Communications Plan—This could be having a specific person identified to contact for status updates or a safe location to meet up with family members.
  • Assemble an Emergency Kit—Have enough food, water and medicine on hand at all times to last you at least three days in the case of an emergency.
  • Know Your Risk—Make sure you know where the flood plains are.
  • Sign Up for Notifications—The Advanced Hydrologic Prediction Service provides RSS feeds for observed forecast and alert river conditions.
  • Prepare Your Home—Use sandbags or other materials to protect your home from flood waters and ensure coverage by contacting your insurance company or agent to purchase flood insurance (do this before flooding happens).
  • Prepare your Family and Pets—Pack in advance; don't leave it until the last minute.
  • Charge Your Essential Electronics—Make sure cell phones and portable radios are all charged and have back up batteries ready.
  • Leave—Don't wait to be ordered to leave; evacuate yourself if your area is going to flood.

Take these steps during a flood:

  • Listen to radio and television including NOAA Weather Radio, check the Internet and social media for information and updates.
  • Get to higher ground.
  • If told to evacuate, do so immediately; lock your home when you leave and if you have time, disconnect utilities and appliances.
  • Don't go into a basement or any room if water covers the electrical outlets or if cords are submerged.
  • Don't walk through flood waters; it only takes 6 inches of moving water to knock you off your feet If you are trapped by moving water, move to the highest possible point and call 911 if possible.
  • Do NOT drive into flooded roadways or around a barricade—Turn Around, Don't Drown—A vehicle caught in swiftly moving water can be swept away in seconds 12 inches of water can float a car or small SUV, 18 inches of water can carry away large vehicles.
Hawaii Braces for Severe Weather—Flash Flooding, Thunderstorms and Dangerous Lightning | U.S.