Tropical Depression Moke Brings Renewed Flood Risk to Hawaii's Big Island

Just one week after Hurricane Lala battered Hawaii's Big Island, Tropical Depression Moke is tracking well south of the islands but still carrying enough moisture to bring renewed flash flooding and mudslide risk to the same areas Lala hit hard.

Moke Tracks South of Hawaii, but Rain Threat Remains

As of late Sunday evening HST, Moke was centered about 420 miles southwest of Honolulu, moving west at 13 mph. While Moke is passing well south of the island chain, unlike Lala's closer track, it's a larger storm, with showers and thunderstorms extending hundreds of miles from its center of low pressure.

A trailing plume of tropical moisture is expected to bring locally heavy rain to the Big Island on Monday and Monday night, raising the risk of localized flash flooding and mudslides, especially in higher terrain and in areas already saturated by Lala's rainfall. Forecasters rated Moke's overall impact potential for Hawaii as low, driven mainly by the flash flooding and mudslide risk on the Big Island.

A general 4 to 8 inches of rain is forecast for the Big Island, with local amounts of 8 to 12 inches possible and isolated totals as high as 24 inches. Hilo may see 2 to 6 inches, while much of the rest of the island chain's higher terrain can expect a general 1 to 2 inches.

High pressure building northeast of Hawaii, strengthened in part by its interaction with Lala farther west, is expected to push dry air southwestward. That should help limit widespread excessive rainfall across the northern Big Island and the rest of the island chain.

Ground Still Saturated From Lala's Record Rainfall

The renewed flood risk comes because the ground across the Big Island remains saturated and some hillsides remain unstable from Lala, with roads and drainage systems in some areas still damaged or clogged with debris. It wouldn't take much additional rain to trigger flash flooding, mudslides or washouts under those conditions.

Lala's rainfall totals were staggering. Hilo received nearly 15 inches of rain from Aug. 14-17, about 1.5 times its entire historical average for the whole month of August. Parts of the Big Island saw 2 to 3 feet of rain, with a maximum observed total of 43.55 inches, and the storm left scattered power outages and wind damage across the island.

Wind gusts from Moke are expected to stay more localized than Lala's, since Moke's center is tracking south of the Big Island and the strongest winds will likely occur in spiral rain bands. Gusts of 40 to 60 mph are possible over higher terrain, with isolated gusts as high as 85 mph. Large breakers, dangerous surf and strong rip currents are expected along the southeast and southern shores, along with some coastal overwash.

What's Next

Elsewhere in the eastern Pacific, several other areas of interest aren't expected to threaten Hawaii directly, but swells radiating outward from them could still create hazards for shipping and fishing interests, along with dangerous breakers for swimmers along the coasts of Mexico and as far north as Southern California this week.

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