Hawaii was bracing for a threat of flooding yet again on Tuesday, with a wet spring storm system expected to bring another five to 12 inches of rain through Friday, as the islands recover from the catastrophic flooding last month.
The National Weather Service issued a flood watch for all the islands from 6 a.m. Wednesday to 6 p.m. Friday, but downpours of rain were already falling over Kauai early Tuesday.
“We could see some flooding today, but the chances increase significantly tomorrow,” Stephen Parker, a meteorologist with the Weather Service office in Honolulu, said on Tuesday.
The service said that “significant flooding” could lead to overflowing streams, road closures and landslides on steep slopes. Mr. Parker warned that evacuations may become necessary.
A flood watch means the ingredients are coming together for dangerous flooding to occur. Mr. Parker said residents and visitors should look out for more urgent warnings that flooding is happening or about to.
Since February, multiple storm systems have led to an unusually wet period across the islands, and most notably two powerful storms led to an onslaught of rain in March.
In the second week of March, soggy hillsides collapsed onto roads, and rivers of rain inundated homes in southern parts of Maui and the Big Island.
When another storm swept in a week later, the ground was already waterlogged, causing more rain to gush and stream down streets. Residents of Waialua on the North Shore of Oahu were forced to evacuate their homes, as floodwaters inundated the area and threatened to overwhelm a local dam. Emergency crews on Oahu rescued more than 200 people, according to the Department of Emergency Management. On Maui, floodwaters destroyed properties in the town of Kihei.
The total amount of rain that has fallen in Hawaii during the past few weeks can be difficult to sum up because of the islands’ complex topography. A mountaintop might receive two feet of rain from a single storm, while a beach nearby may get only a few inches. But experts agree that the last two months marked some of the state’s rainiest periods in recent memory.
Hana, a town on Maui’s eastern coast, recorded over 40 inches of rain in February and March — the highest amount ever measured in this time span.
The city of Honolulu warned that areas still recovering from the last round of flooding would be at risk again, including Waialua, Haleiwa, Kahuku and Laie.
“This comes at a time when many of our communities are still working to recover, and we understand how difficult that is,” Mayor Rick Blangiardi said in a statement.
The storm that was developing to the northwest of Hawaii on Tuesday is expected to bring moderate to heavy showers, initially impacting Kauai and Oahu and spreading across all the islands by Wednesday. The storm will also bring a chance for thunderstorms and generate strong winds, particularly on Thursday.
Mr. Parker said some locations could see rainfall rates of two to four inches per hour, bringing the highest chances for significant flooding to these locations.
“It’s just impossible in advance to tell where those setups are going to occur,” he said.
A winter storm watch will also go in effect Wednesday morning with a chance of freezing rain and snow on the summits of Mauna Kea and Mauna Loa on the Big Island above 12,500 feet, lasting through Friday afternoon as well. Snow is not unusual on the island’s highest peaks in winter.
Forecasters referred to the March storms as Kona lows, named for the winds that affect the leeward (“kona” in Hawaiian) sides of the islands. There’s some disagreement around whether the term should be used to define this next system.
“It’s all semantics,” Patrick Blood, a meteorologist with the Weather Service, said. “The message is that the impacts from this system will be the same with flooding in areas that have already been hit hard.”
Amy Graff is a Times reporter covering weather, wildfires and earthquakes.
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