Heavy Rain, Flooding Forecast as Iselle Approaches Hawaiʻi

Satellite imagery of Iselle (far right) at 8:30 a.m. HST, Tuesday, Aug. 5, 2014. Image courtesy CPHC/NOAA/NWS.

By Wendy Osher

(Posted: 9:23 a.m. HST Tuesday, 8/5/2014)

Hurricane Iselle is now listed as a Category 3 hurricane. It was last located about 1050 miles ESE of Hilo Hawaiʻi; 1160 miles ESE of Kahului, Maui; 1210 miles ESE of Kaunakakai, Molokaʻi; and 1185 miles ESE of Lānaʻi City.

As of 5 a.m. on Tuesday, Aug. 5, 2014, the system was moving west at 9 mph and had sustained winds of 125 mph with hurricane force winds extending up to 35 miles from the center; and tropical storm force winds extending outward up to 115 miles, according to the latest forecast issued by the National Hurricane Center.

Forecasters with the NHC say the system should turn toward the west/northwest at a faster forward speed later today and Wednesday, and is forecast to undergo some weakening during the next 48 hours.

Administrators with the State Emergency Management Agency say Iselle will likely impact the islands sometime on Thursday afternoon as a tropical storm, and will leave the state late Friday to early Saturday. County officials say they expect the system to impact Maui County as a tropical storm beginning early Thursday evening.

Iselle 5-day track 5 a.m. HST (8 a.m. PDT), Tuesday, Aug. 5, 2014. Image courtesy CPHC/NOAA/NWS.

FLOOD POTENTIAL HYDROLIC OUTLOOK:

At 3 a.m., the National Weather Service issued a Flood Potential Outlook for the state saying heavy rain and flash flooding are possible Thursday and Friday.

“The latest forecast for Hurricane Iselle takes the system over the island chain as a gradually weakening tropical cyclone. While Iselle is expected to be moving steadily west as it passes through the island chain, abundant moisture drawn into the circulation will bring the potential for very heavy rainfall and flash flooding on Thursday and Friday,” according to the National Weather Service.

Forecasters with the NWS say details, timing, location, and amount of rainfall remain uncertain, and are “highly dependent on the eventual track of Iselle.”  The agency says that an updated outlook will be issued this afternoon, and could be replaced by a flash flood watch later today if conditions warrant.

Tropical Storm Warning image, 6 a.m. HST 8/5/14. Image courtesy National Weather Service.

TROPICAL STORM WARNING:

At 6 a.m., the National Weather Service issued a tropical storm warning for offshore waters between 40 and 240 nautical miles around Hawaiʻi, including the Papahānaumokuākea Marine National Monument east of the French Frigate Shoals.

The tropical storm warning states that individual waves may be more than twice the significant wave height (the average height of the highest 1/3 of waves).

Today, seas of 6 to 8 feet and E winds of 15 to 20 knots are expected north of 19-degrees N; and seas of 8 to 11 feet and E winds of 20 to 25 knots are expected south of 19-degrees N. Thursday through Friday, tropical storm conditions are expected, and hurricane conditions are possible on Saturday for the area east of 154-degrees W.