Another out-of-season storm is brewing near Hawaii and is likely to deliver much heavier rain than the first, as an atmospheric river will become involved, AccuWeather meteorologists warn.
A storm locally called a Kona Low, which is a storm in the middle levels of the atmosphere, brought rounds of rain to parts of the islands from late last week to Mother's Day weekend. Up to several inches of rain brought localized flooding to Oahu and Kauai.
Earlier this spring, another Kona Low brought tremendous rainfall and flooding to part of the island chain. In a matter of hours, the storm unleashed rainfall equal to seven times that of the entire month of April in Lihue, Hawaii, and five to 10 times the April historical average on the island of Kauai. Honolulu received two times the April average from the storm in mid-April.
"Kona Lows are more common during the late fall through the early spring, so the one from this past weekend is a bit out of season," AccuWeather senior meteorologist Brett Anderson said. "This is typically the dry time of the year around Hawaii before trade wind showers and tropical downpours ramp up."
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As if one Kona Low was not enough, a new and bigger one is in the works and will affect the islands from the middle of the week to perhaps the entire weekend.
"A very powerful Kona Low is set to bring flooding rain to portions of Hawaii starting Wednesday," AccuWeather meteorologist Alex DaSilva said.
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"While the heaviest rainfall is forecast to occur from Maui to Ni'ihau from Wednesday to Friday along the south- and west-facing mountainsides, the Big Island can still see periods of heavy rain, especially in the higher terrain," DaSilva explained.
Heavy rain on these sides of the islands is atypical, as the northeast trade winds tend to bring soaking rains on the northern and eastern sides and slopes.
There is the likelihood that a long plume of moisture, called an atmospheric river, will extend from near the equator northward through the islands later this week and into this weekend. Depending on the intensity and persistence of that atmospheric river, rainfall could be excessive.
"Localized areas in the higher terrain in some of the islands could receive rainfall amounts over 10 inches, which could cause life-threatening flash flooding and mudslides," DaSilva said.
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| Map of Hawaiian Islands. (United States Geological Survey/USGS) |
Winds can be very strong in the higher elevations as well.
"Because this Kona Low is forecast to be more powerful than what is typical, it will bring strong winds, especially over the higher elevations," DaSilva added. "Along with triggering large swells from the northwest that can create overwash along the coast with dangerous rip currents from the middle of the week through the weekend."
The most concentrated plume of moisture associated with the atmospheric river will tend to shift farther to the west over the weekend, so the worst conditions may be limited to Kauai and Ni'ihau starting on Saturday. However, since the plume may broaden as it shifts, showers can still be scattered about the islands this weekend, and localized heavy rainfall with flash flooding may continue.
The Kona Low itself may wander farther to the west and weaken next week, allowing the rain to move west of the populated islands in Hawaii.
