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Flash flood warning posted for Oahu

  • KRYSTLE MARCELLUS / KMARCELLUS@STARADVERTISER.COMClouds covered the North Shore skies in Kahaluu on the morning of Sunday, October 19, 2014.
    KRYSTLE MARCELLUS / KMARCELLUS@STARADVERTISER.COM
    Clouds covered the North Shore skies in Kahaluu on the morning of Sunday, October 19, 2014.

The National Weather Service issued a flash flood warning for Oahu after weather spotters reported flooding from heavy rains along the south shores of Honolulu.

Radar showed the area of heavy rain moving north over the island at 10 mph. A flash flood warning means flooding is imminent or occurring in streams, roads and low-lying areas. Residents are warned to remember the adage “Turn around, don’t drown,” and to not cross fast-flowing or rising waters in vehicles or on foot.

The warning is in effect until 2 p.m.

The stormy weather is lingering over Oahu as Hurricane Ana began moving south of Kauai and Niihau Sunday morning. Kauai County remains under a tropical storm warning.

Ana’s winds dropped to about 75 mph, with higher gusts at 11 a.m. Sunday. The center of the category 1 hurricane was about 120 miles south-southwest of Lihue and 180 miles west-southwest of Honolulu, moving to the west at 9 mph. The tropical storm force winds extend 105 miles from the center and hurricane force winds extend out 25 miles.

Hurricane Ana was expected to pass about 65 miles southwest of Niihau about midday Sunday.

Forecasters said that tropical storm conditions — heavy rain, winds of 39 mph or higher, and rough surf — are expected in Kauai County, mainly near Niihau. A storm surge of up to 2 feet is expected and surf on south and north shores of 10 to 15 feet is predicted.

Winds across Niihau may reach 35 to 45 mph with gusts to 60 mph, the National Weather Service said. Winds across Kauai may reach 25 to 35 mph, with gusts to 50 mph.

Forecasters dropped a tropical storm watch for Oahu and a flash flood watch for the Big Island early Sunday as the storm moved west. But all other islands remain under a flash flood watch until 6 p.m. Sunday.

Forecasters said rain bands from the hurricane could produce 3 to 6 inches of rain, perhaps up to 8 inches in some areas of Kauai and Niihau.

“If these amounts occur within a short period of time, flash flooding may occur,” forecasters said. “In addition to possible flash flooding, excessive runoff may result in rock and mudslides in steep terrain.”

Ana began slowing down Saturday night, before picking up speed late Sunday morning and finally starting a gradual turn to the west, away from Kauai County, Sunday morning.

North and west-facing shores of Oahu and Molokai, and north shores of Maui are under high surf advisories.

The National Weather Service said swells generated by Hurricane Ana and a North Pacific storm will bring 10 to 15 foot waves on north shores; 8 to 12 foot waves on west shores and 6 to 9 foot waves on south shores through Sunday night.

High surf advisories for Lanai, Kahoolawe, West Hawaii island and south shores of Maui were canceled after surf dropped below advisory levels.

Forecasters expect Ana to remain a hurricane as it passes through the Northwest Hawaiian Islands. Tropical storm warnings and a hurricane watch are posted for the Papahanaumokuakea marine national monument and for waters around Kauai and Oahu.

Even though Ana passed by the Big Island Saturday morning, heavy rains continued into Saturday night.

The Hilo Airport got record rainfall of 4.55 inches for the date on Saturday, breaking the old record of 2.08 inches set in 1990.

In the 24-hour period ending at 5 p.m.Saturday, 11.4 inches fell at the Mauna Loa Observatory; just under 8 inches fell at the Pali 2 station in the Kau Desert south of Kilauea Crater and in the Kulani National Wildlife Reserve.

Overnight, 3.5 inches fell on Kula, Maui in the 24-hour period ending at 5 a.m. On Oahu, 3.9 inches soaked Poamoho and 2.8 inches was recorded at the Lyon Arboretum in Manoa.

Tropical storm and hurricane warnings are in effect for the ocean around Kauai County aand more than 40 miles offshore of the main Hawaiian Islands. Forecasters said strong thunderstorms capable of producing waterspouts could form over coastal waters overnight.

The forecast for Oahu and Kauai calls for cloudy skies and frequent showers with a chance of thunderstorms and locally heavy rain. Winds of 15 to 30 mph with higher gusts are possible through Sunday.

Maui can expect similar conditions with lesser winds. Big Island skies will be mostly cloudy with scattered showers.

On Oahu, Mayor Kirk Caldwell urged people to stay out of the ocean and off mountain trails until the wave and rain danger is gone.

Central Pacific Hurricane Center meteorologist Ray Tanabe said the surf, which was small at 8 a.m. Saturday and began rising quickly by 10 a.m., was choppy and rough. 

“It could be dangerous, even for folks on the beach,” Tanabe said. Because Hurricane Ana is so close to the islands, the waves may run together and one wave may break as an earlier wave is still washing up on shore.

That means the water may sweep further up the beach and could pull someone on shore into the water, Tanabe said.

Gusty winds — a combination of stronger than usual tradewinds from the east and some storm-related winds from the south — will add to the choppy surf conditions. 

There’s also a chance of thunderstorms, Tanabe said.

“If you are in the water and you hear thunder and you see lightning, you don’t want to be in the water,” Tanabe said.

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