Honolulu – Hawaii's famous sun will be on a vacation of its own this week as a day-long storm pattern develops just off the coast of the tropical islands, threatening heavy rain and flash flooding over the weekend.
“This week's (forecast) model guidance appears to be typical mid-May for Hawaii, to say the least,” Honolulu National Weather Service forecasters said during a forecast discussion Tuesday morning.
The Kona Low is expected to form hundreds of miles north of the island Tuesday evening and is expected to strengthen over the next few days and snake just offshore.
“Kona” comes from the Hawaiian word for “leeward,” or the side protected from the typical northeast trade winds. The Kona Depression is problematic because its winds blow in the opposite direction of typical trade winds, bringing heavy rain to the leeward areas of the islands that are normally shadowed by wind and rain.
What is “Konaro”?
Meanwhile, just southwest of the island, there is a large area of deep, tropical moisture that provides enough fuel to increase rainfall near the Kona Low.
This combination will likely result in an extended period of heavy rain and thunderstorms through at least the weekend.
A flood watch will be in place across the Hawaiian Islands from Wednesday morning through Friday evening. The heaviest rain is expected on Oahu and Maui on Wednesday and Wednesday night, gradually moving west into Kauai by late Friday.
The NWS warned that flooding rivers and drainage ditches could cause major flooding and road closures in some areas. Spills can also cause property damage in urban areas.
“Landslides may occur even in areas with steep terrain,” the NWS said.
It's already been a very wet week for Hawaii. Flood watches and warnings were issued for the islands last weekend as a slow-moving storm battered the islands and winter storm conditions persisted on the Big Island's peaks.
Powerful storm in Hawaii brings severe weather threat to islands, winter storm warning to mountains
Even on Monday ahead of the Kona Low, flash flood warnings were issued for eastern Oahu as strong thunderstorms dumped 2 inches of rain per hour, causing localized flooding.
Some rain gauges in the highlands of Oahu have reported more than 8 inches of rain in the past 72 hours, and a rain gauge at St. Stephen's Seminary near Kailua has seen more than 18 inches of rain fall over three days. The Kaneohe gauge measured over 9 inches in 72 hours, while the Marine Corps Base at Kaneohe reported 5.01 inches during the same period.
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Wednesday's flood warning currently expires Friday night, but the NWS warned the rain pattern could continue into the weekend.