After the first two months of the wet season — October and November — got off to a slow start, December “appears to have made up for lost ground,” according to Kevin Kodama, senior hydrologist for the National Weather Service in Honolulu.
A “kona low” pressure system, a strong subtropical cyclone that hit the state last month, was “one of the strongest to affect the state of Hawaii in the last 50 years,” Kodama said in his final monthly precipitation summary for 2021.
On Dec. 6, several normally dry gulches in Ka‘u District flooded, and Highway 11 closed at Kawa Flats for a few hours.
Even after the “kona low” weakened on Dec. 8, strong tradewinds and unstable conditions aloft “maintained enhanced rainfall through Dec. 22, especially along the windward slopes of the Big Island and Maui,” Kodama said.
Every official rain gauge in Hawaii County recorded above average totals in December, with the Papaikou Well gauge sporting the highest total, at 30.26 inches, almost twice its average for December.
According to Kodama, annual rainfall totals for the Big Island were “near- to above-average at most of the gauges.”
Hilo International Airport’s 24.99 inches — more than twice its norm for the month — marked its highest December rainfall total since 2008 and its sixth highest December total on record. That resulted in 137.97 inches of rain for the year, 15% of Hilo’s yearly average of 120.39 inches.
Piihonua, in the foothills above Hilo, recorded the rainiest 2021 of any Big Island location. Its 24,46 inches of rain in December brought its yearly total to 201.88 inches, 9% higher than its yearly average of 185.75 inches.
Glenwood tallied 26.52 inches of rain last month. The village in the upper Puna rainforest is almost always Hawaii Island’s rainiest populated spot. That didn’t hold true this year, although it did receive 199.7 inches for the year — which is just 86% of its normal 233.53 inches.
Pahoa received 28.5 inches of rain for the month, its “highest December total on record,” according to Kodama. Its total of 159.9 inches for 2021 was 117% of its yearly norm of 136.83 inches.
While rainfall totals were lower in West Hawaii, all four Kona coffee belt rain gauges received double or close to double their December rainfall, led by Honaunau with 5.7 inches. Kodama said Honaunau’s 80.06 inches for the year was its “highest annual total on record.”
Kealakekua recorded 5.43 inches for the month and 79.77 inches for the year, 142% of its yearly average of 56.14 inches. Kainaliu measured 4.91 inches for the month, bringing its 2021 total to 62.68 inches, 15% above its yearly norm.
The fourth coffee belt gauge, Waiaha, received 5.4 inches in December, but its yearly total is missing.
Ellison Onizuka Kona International Airport at Keahole, where visitors almost always arrive to sunshine, recorded 1.98 inches of rain in December, 187% of its usual 1.06 inches for the month. The final month’s rainfall brought the busy airport’s total to 13.62 inches for the year, 138% of its annual average 9.87 inches.
In Ka‘u, Kapapala Ranch received 71.15 inches for the year, 134% of its normal annual rainfall of 53.32 inches, while Pahala checked in at 61.12 inches, a little more than 4 inches above its average yearly rainfall of 57 inches.
Some Big Island gauges didn’t share in the bountiful rainfall.
Puuanahulu, in North Kona, totaled just 15.22 inches, 59% of its average of 25.74 inches. And in South Kohala, always arid Waikoloa had 95% of its usual rainfall for the year with 12.08 inches, slightly more than an inch a month.
Email John Burnett at jburnett@hawaiitribune-herald.com.