Slow-moving storm drenches Hawaii; New storm looms

AccuWeather's Enhanced RealVue™ Satellite image from Sunday evening, May 12, 2024, shows clouds (green and yellow shading) to the northeast of the Hawaiian Islands, associated with a storm in the upper part of the atmosphere.

AccuWeather forecasters say that the Hawaiian Islands are in for a wet stretch as a storm parks over the tropical paradise, resulting in daily rounds of drenching showers and thunderstorms into Monday. A bigger storm is forecast to arrive later this week and may trigger an atmospheric river with major flooding.

A storm in the upper part of the atmosphere was located to the northeast of the island chain as of Sunday evening, local time.


"The storm will act to enhance shower and thunderstorm activity. Some of the strongest thunderstorms could even contain gusty winds," AccuWeather Meteorologist Joseph Bauer said.

A pool of cool air high in the atmosphere will also create a conducive environment for hail to form.

The traditional northeast trade wind pattern, which is the dominant force behind the weather in Hawaii, will be disrupted in the pattern. These trade winds create wet conditions on the northern and eastern sides of the islands. As moisture is wrung out over the mountains, much less rain falls on the southern and western sides.

Showers will likely persist, just as likely on either side of the islands, into Monday.

In some communities, the deluge can result in worse conditions than just a bad day at the beach.

"The repeated rounds of showers and thunderstorms, especially over areas that are not acclimated to receiving as much rainfall, could lead to flooding concerns and can lead to increased streamflows on area streams and creeks," Bauer said. Road closures are possible as a result of the rapid runoff and overflowing streams, as well as due to debris flows.

By early Friday morning, nearly 7 inches of rain had accumulated over the Koʻolau mountains on the northeastern side of the island of Oʻahu, according to the National Weather Service. This surge of water caused the Waiahole Stream to reach minor flood stage over the course of several hours Thursday night.

AccuWeather experts urge residents and visitors to be cognizant of weather alerts for their region and heed all evacuation notices. Flooding can occur even in areas missed by the heaviest rainfall, especially in lower-elevation towns downstream of higher terrain.

AccuWeather meteorologists are closely monitoring the likelihood of more rain beginning in the Hawaiian Island chain as early as Wednesday but ramping up into Friday and continuing into the weekend.

"One key difference with the new storm brewing will be the potential for an atmospheric river to set up and stall over part of the islands," AccuWeather Senior Meteorologist Alex Sosnowski said.

An atmospheric river is a long plume of moisture that often extends from the Tropics to the intermediate latitudes. This acts as a conveyor belt or firehose effect of heavy rainfall.

"Should the setup evolve to its full potential, many inches of rain may be released in a matter of hours on some of the southwest-facing slopes of the mountains on the islands, which would lead to major flash flooding or perhaps even a flooding disaster," Sosnowski warned.

"The position of the parent storm, well to the northwest of the islands, may lead to rare northwest swells and heavy wave action along the northwest-facing beaches and coastal areas," AccuWeather Meteorologist Alex DaSilva added.

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