Drenched: West Hawaii’s Wet Summer ContinuesOctober 4, 2019, 5:36 PM HST (Updated October 4, 2019, 5:36 PM)
The wet season will soon begin to dissipate in the Kona Districts, just as it takes hold across the rest of the state. But wet weather on Kona slopes has made clear in recent weeks it won’t be ushered quietly into the offseason.
Between the months of May and September, rainfall totals have skyrocketed at sites across West Hawai‘i. Numbers provided by the National Weather Service (NWS) in Honolulu show that Waiaha, which is located near Holualoa, saw 59.97 inches during that timeframe — 241% of the area’s average rainfall for the season.
Kainaliu was hit with 39.38 inches of rain this summer, 129% of the normal average. Mostly afternoon clouds dropped 54.62 inches on Kealakekua, 174% of the average for the region. Honaunau was splashed with 45.95 inches of rainfall throughout the season, which totals 151% of the area’s average precipitation. And Puho CS, at Pu‘uhonua O Honaunau, was doused by 18.91 inches of rain, 127% of its normal average.
Kevin Kodama, a hydrologist with NWS, said the extra-wet weather is due to a combination of higher-than-average ocean temperatures across the state and the absence of vog since Kīlauea returned to a resting state following more than three decades of constant eruption.
“The vog pooled in Kona, and all the particulates in the air (meant) more particles for water to grab onto,” Kodama said. “That makes rainfall less effective.”
Higher ocean temperatures, caused in part by an El Nino cycle that passed through Hawaiian waters this summer, have led to a coral bleaching event already taking place throughout the islands. The warmer water also funnels more moisture up the Kona slopes, which typically leads to afternoon showers — the sort West Hawai‘i has seen more or less daily for the past two weeks.
“For the second consecutive month, all four gages in the Kona coffee belt region logged more than 10 inches of rainfall,” Kodama wrote in his precipitation summary report. “However, none came close to breaking September records because of the high bar set by the results in 2015.”
The summer of 2015 also saw high ocean temperatures and marked the most catastrophic coral bleaching event in history.
The highest daily rainfall total on Hawai‘i Island for the month of September belonged to Honaunau, which recorded 2.74 inches of precipitation on Sept. 2.
“The Kohala Ranch (monthly) total of 7.66 inches was notable since it was more than 10 times its average for September,” Kodama wrote. “This rainfall did not occur in one event but involved four separate days during the month with more than one inch recorded.”
Kodama said it’s difficult to say how much of Kona’s wetter-than-normal wet season should be attributed to exceedingly warm ocean temperatures versus the change in air quality across West Hawai‘i. In any case, he added, rainfall should begin to taper off across the region as October fades into the winter months.
The West Hawai‘i region is unique throughout the state, as its wet season is distinctly summer. The rest of Hawai‘i experiences its wet season from October through April.
Rainfall totals on the Big Island’s windward side were generally near or below average in September, according to Kodama’s monthly precipitation report. The USGS’s Saddle Road Quarry gage had the highest monthly total of 15.25 inches, which is 155% of its average.
The USGS’s Saddle Road Quarry rain gage also owns the island’s highest year-to-date total of 128.98 inches, which is 124% of the area’s average.
An NWS map of year-to-date rainfall is available online.