‘La Nina hasn’t hit us yet, but it’s trying to’

Low-pressure systems affecting Hawaii Island in the second half of last month gave the impression of a wetter-than-usual October, but most Big Island rain gauges logged average or slightly below-average rainfall for the month.

That’s according to the monthly precipitation report prepared by Kevin Kodama, senior service hydrologist for the National Weather Service in Honolulu.

We had the slow start to the wet season that we’d predicted, but in the second half of October we got the rain,” Kodama said Thursday.

“La Nina hasn’t hit us yet, but it’s trying to.”

At 8.17 inches, Hilo International Airport recorded two-plus inches less of rain that its October norm. At 83.14 inches, the airport’s year-to-date rainfall at the end of the month, was at 89% of its usual 93.93 inches.

Two rainier spots upslope of Hilo, Piihonua and Waiakea Uka, received 13.91 and 13.69 inches, respectively, 99% of the October norm for Piihonua and 92% for Waiakea Uka. Both are also sporting what appears to be robust rainfall totals for the first 10 months, with Piihonua checking in at 135.32 inches and Waiakea Uka 136.45 inches, 90% of the year-to-date norm for the former and 85% for the latter.

Pahoa measured slightly above its normal October rainfall, with 12.18 inches. That brings Lower Puna’s largest village to slightly more than 100 inches for the year, 92% of its year-to-date average.

Forecasters have predicted a La Nina weather pattern to emerge in the tropical Pacific later this month. During La Nina events, trade winds are even stronger than usual, leading to more rainfall over the windward slopes of the Big Island.

Unlike most of the state, the upper Kona slopes — which includes the Kona coffee belt — have their dry season from the autumn going into the winter, and their rainy season in the summer.

All four of Kona’s official coffee belt gauges — Honaunau, Kealakekua, Waiaha and Kainalu — registered total rainfall far below normal October totals. Honaunau had the wettest October at 2.97 inches, just 58% of norm, while Kainalu experienced the driest month at 1.57 inches, a paltry 37% of average.

“They’re starting to see their dry season there,” Kodama said of the coffee belt. “But if we get La Nina and the weather systems that are predicted for later, the’ll see a wetter-than-average dry season over the Kona slopes.”

Leeward gauges were predictably dry for most of October, although some spots enjoyed their monthly rainfall quota.

Ellison Onizuka Kona International Airport in Keahole, where the tarmac is almost perpetually drenched in sunshine, was right at its October rainfall norm at 0.9 inches. Kaloko-Honokohau National Historical Park was blessed with 1.86 inches last month, 27% above its average. And Kohala Ranch reported 1.2 inches of rain — but that’s twice its usual October amount.

Portions of the Kohala Coast are in moderate drought while most of the leeward Big Island is experiencing abnormally dry conditions as of Thursday, according to the state Department of Land and Natural Resources’ drought monitor.

Email John Burnett at jburnett@hawaiitribune-herald.com.