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Hilo on record pace for rainfall

With a wetter-than-average October, the Big Island continued its unusually rainy year, although drier months might be on the horizon.

According to official rainfall data from the National Weather Service, many Big Island rain gauges saw their wettest October on record, with most rain gauges still recording higher-than-average rainfall this year to date.

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Kevin Kodama, senior service hydrologist for the National Weather Service’s Honolulu forecast office, said in October there were a number of upper-lever disturbances that caused a significant amount of atmospheric instability. Combined with a high amount of low-level moisture, conditions were conducive for frequent rainfall on the island.

The Saddle Road Quarry rain gauge received the most rain on the island in October, with 32.1 inches, nearly 300 percent of its average October rainfall. This year to date, the Saddle Road gauge has received 340 inches of rain.

Hilo International Airport, meanwhile, received 153 inches this year so far, 18 of which were recorded in October alone. The Hilo airport gauge is on pace for its total 2018 rainfall to rank among its top 10 rainfalls recorded since 1949.

Papaikou, Glenwood, Waiakea and Piihonua rain gauges all received about 30 inches of rain in October, and have all received more than 200 inches so far this year.

Only four windward rain gauges — Kamuela, upper Kamuela, Kahua Ranch and Waimea — recorded less-than-average rain in October. Of those, only Waimea and Kahua Ranch have received less-than-average rain so far this year.

On the leeward side, nearly all rain gauges received between 200 percent and 500 percent of their October averages. While Ellison Onizuka Kona International Airport at Keahole received 1.86 inches of rain, 139 percent of its average, areas such as Keaumo, Pali and Kapapala received about 20 inches each despite usually receiving only 4 inches. Keaumo had the greatest deviation from its average, with the gauge recording 520 percent of its monthly average.

Most leeward sites have received above-average rainfall this year so far, with only the Kona airport, Kainaliu, Kealakekua, Puho, Kahuku Ranch and lower Kahuku reporting less-than-average rainfall.

Kodama was hesitant to attribute the consistently wet year to climate change, saying that although the high moisture levels were partly driven by above-average sea surface temperature, the Big Island also has “seen wetter conditions.”

Kodama pointed out that although some gauges broke their October records, those records only extend back about 30 years.

November is expected to be similarly wet, Kodama said, but December might see the beginning of the influence of El Nino, the periodic warming weather pattern that affects the Pacific Ocean every several years.

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El Nino could lead to drier winter months on the Big Island, Kodama said.

Email Michael Brestovansky at mbrestovansky@hawaiitribune-herald.com.