Kona Low expected to bring rainfall, with possible flooding, to Big Island starting today

This story was updated at 10:27 a.m. Nov. 29.

On Tuesday, a maturing Kona Low to the northwest of Kaua‘i was already bringing heavy rains and the possibility for thunderstorms to western portions of the Hawaiian Islands.

The Kona Low has the potential to also bring heavy rainfall, thunderstorms and flash flooding to the Big Island beginning Wednesday as the storm system continues to draw tropical moisture from the south through the islands.

A flood watch for the entire state — including the Big Island — is in effect until Thursday afternoon. It was issued in anticipation of drenching rainfall, which is possible through Friday as the Kona Low drifts slowly west, away from the state, and gradually weakens.

Fortunately, no widespread damaging winds are expected from the storm; however, any thunderstorms that develop could produce gusty conditions.

While there is no particular area of the Big Island under more threat from the storm than others, with moisture being pulled from south of the state, areas in Kaʻū and Puna could see more widespread rainfall over larger areas.

John Bravender, warning coordination meteorologist with the National Weather Service forecast office in Honolulu, said thunderstorms are possible anywhere around the island, bringing with them the potential for flash flooding.

Areas suffering from drought are of particular concern, as the chance for flash flooding increases because any rainfall heavier than about 1 inch per hour hitting dry, crusted land would simply run off instead of being absorbed.

Bravender said the wet season, which started in October, has been pretty quiet until now. The flash flood watch in effect for the entire state is the first the National Weather Service has issued so far this wet season.

October was an extremely dry month throughout the islands and more than 80% of the Big Island is suffering from severe drought.

“What we’re keeping an eye out for and what we’re worried about are those heavier rainfalls that could see rains 2, 3, 4 inches per hour in thunderstorms that would be just too much to sink in,” Bravender said.

The storm triggered a flood advisory for Kaua‘i for part of Tuesday as embedded thunderstorms were dumping up to 2 inches of rain per hour on the Garden Isle. A thunderstorm with wind gusts of up to 40 mph also moved over parts of Ni‘ihau early Tuesday afternoon.

Rainfall totals will be higher over the western half of the state because Kaua‘i and O‘ahu are closer to the storm system, but people elsewhere should still be prepared for the possibility of flooding.

“I don’t want anybody on Maui or the Big Island to get a false sense of security because we’ll see heavy rain pick up there as well and we could see embedded thunderstorms,” Bravender said. “So even if you don’t get a lot of rain over a prolonged period of time, even intense rain for a short period of time can cause flash flooding.”

Hawai‘i County is preparing for potential impacts from the storm.

Waipi‘o Valley Access Road is closed to the general public beginning Wednesday as a precautionary safety measure; however, the road remains open to valley residents and farmers unless otherwise directed.

The public will be notified when the road is reopened.

The County and its partners also are prepared to open shelters in Kaʻū and South Kona should the need arise.

As of now, camping permits have not been canceled. However, residents and visitors should exercise caution and stay updated about weather developments.

Additionally, the Hele-on bus service will be monitoring the situation closely. Routes might be canceled at any time for safety purposes, pending the severity of the weather. Passengers are advised to check for updates on bus service availability and plan accordingly.

Hawai‘i County Civil Defense also is coordinating with state agencies to ensure a fast response should any emergencies happen.

“We are closely monitoring the development of the Kona Low and are working diligently to ensure the safety and well-being of our community,” Hawai‘i County Mayor Mitch Roth said. “I encourage everyone to stay informed through official channels, heed warnings and make necessary preparations to protect themselves and their property.”

The County offered several precautionary tips:

• Monitor official weather updates from the National Weather Service and local authorities.
• Have an emergency kit ready to go that contains essential supplies such as food, water, medications, flashlights, batteries and important documents.
• Establish a communication plan with family members and loved ones in case of evacuation or separation.
• Secure outdoor furniture and loose objects.
• Ensure gutters are clear to prevent flooding.
• Familiarize yourself with evacuation routes and shelters in your area.

The County will continue to provide updates and information through official channels, including social media, local news and the emergency notification system.

The Hawai‘i Tourism Authority also echoed Hawai‘i County’s advice, urging people to be aware of weather-related impacts such as flash flooding and hazardous driving conditions. Swimmers should exercise caution and consult any lifeguards on duty about ocean conditions.

For up-to-date beach information, click here.

To register for Hawai‘i County’s Everbridge notification service, click here. You can find the official County hazard map here.