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October: Wet in East Hawaii, dry in West Hawaii

October rainfall totals for the Big Island paint West Hawaii as sun-drenched and East Hawaii as simply drenched.

According to the monthly summary by Kevin Kodama, senior service hydrologist for the National Weather Service in Honolulu, the majority of rain gauges on the windward side of the Big Island recorded normal to above-normal totals for October, the first month of the wet season.

Conversely, not a single gauge on the island’s leeward side recorded the monthly average for October, with the majority of locations reporting only a fraction of the rainfall they would receive in a typical October.

Kodama said the abundant rain in East Hawaii was produced by “persistent trade winds across the main Hawaiian Islands through Oct. 18.”

He added that an “area of deep tropical moisture” moved over windward slopes on the evening of Oct. 11 and into the early morning of Oct. 12, bringing 10 to 15 inches of rain from the Upper Waiakea Forest Reserve northward to the Halakau Forest National Wildlife Refuge.

“Some of the heavy rainfall went far enough upslope to produce multiple areas of runoff debris on the Maunakea Access Road,” Kodama said, adding the road had to be briefly closed above Halepohaku at the 9,300-foot level of the mountain.

Hilo had some minor flooding and a few partial road closures.

The second half of the month produced much drier conditions on the windward side.

The Papaikou Well gauge recorded the highest rainfall total, 20.66 inches, or 131% of its average October total.

Hakalau registered 16.04 inches, more than three times its October norm — and its wettest October since the site started reporting its rainfall in 2004.

Two locations reporting slightly less-than-average rainfall were Hilo International Airport, with 9.47 inches, or 92% of its October average, and Pahoa, with 10.77 inches, 93% of its normal total for the month.

Both sites were at 114% of their year-to-date average for the first 10 months of the year, with Hilo reporting 107.09 inches and Pahoa tallying 125.03 inches.

Conversely, the Kona coffee belt — which normally has its dry season in the fall and winter —was positively parched in October.

Honaunau and Kealakekua reported their driest October since 1995. The former measured 0.88 inches of rain, or just 17% of normal, while the latter collected 0.65 inches, only 15% of its October average.

The other two coffee-belt gauges were similarly dry, with Kainaliu at 0.54 inches, 13% of its norm, and Waiaha reporting 1.03 inches, 30% of average.

Other West Hawaii locations also reported arid conditions for the month.

Ellison Onizuka Kona International Airport received a scant 0.02 inches of rain on its tarmac, while Kaloko-Honokohau National Historical Park recorded just 0.03 inches of rain. Both totals are just 2% of those locations’ average rainfall for the month.

Dry conditions also persisted in Ka‘u and Kohala.

Pahala received just 1.2 inches of rain last month, less than a quarter of its normal October total, while Kohala Ranch reported 0.04 inches of rain, just 7% of its average for the month.

Email John Burnett at
Source: Hawaii Tribune Herald

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