Hawaii Tribune-Herald
By John Burnett
For much of May, most of Hawaii Island’s rain gauges were measuring near- to below-average amounts of rainfall, as the National Weather Service in Honolulu predicted in its dry season outlook for May through September.
There was one notable exception — the Kona coffee belt, which experiences its wet season in the summer. That said, it was even wetter than usual.
And one coffee belt gauge, Kealakekua, posted its highest May rainfall total on record, 12.86 inches, 240% of its average May rainfall total, and over 3 inches more than the previous May record, 9.76 inches.
“It didn’t just squeak by on the record; it was a significant margin, so it’s pretty notable,” Kevin Kodama, NWS senior service hydrologist, said Thursday. “And it wasn’t just that site. All of the gauges in that area picked up a pretty good amount. You look at the percent of averages, it was all at, above, or just below 200% of average.”
Kealakekua also had the Big Island’s highest one-day rainfall total of 2.28 inches on May 3.
The other three official coffee belt gauges Kodama referred to are: Kainaliu, which registered 10.57 inches, 204% of its May norm; Honaunau, which measure 9.33 inches, or 196% of average; and Waiaha, which had 7.94 inches, 170% of its usual May.
One unofficial leeward gauge, at Holualoa, in upslope North Kona, tallied 14.99 inches.
“May is just getting things started. Actually, the peak doesn’t occur until later,” Kodama said of the summer wet season for leeward slopes. “So it’s pretty early to be ramped up like this. Overall, we’ve had some instability, but they’ve been getting rain, like, everyday — and in decent amounts.”
Not all Kona locations shared in the rainfall bounty, however.
Ellison Onizuka Kona International Airport at Keahole, where tourists on the tarmac are almost always greeted by sunshine, registered just 0.9 inches for the month, 45% of its usual 2 inches. Puuanahulu was even drier at 0.77 inches, just 34% of its May average of 2.25 inches.
Windward monthly totals were mostly in the range of 60% to 100% of average. Glenwood, in the upper Puna rainforest, had the highest monthly total of 13.74 inches, 86% percent of average.
The rain gauge at Hilo International Airport tallied 6.17 inches, just 76% of its May average of 8.12 inches. Due to a wetter-than-average rainy season, however, the airport’s year-to-date total of 69.56 inches is 134% of its average for the year’s first five months, 51.91 inches.
Piihonua, in the foothills above Hilo town, hit double-digit rainfall in May, checking in at 10.78 inches, 80% of its May norm of 13.48 inches. Piihonua also has the distinction of being the first official NWS rain gauge on the Big Island to crack triple digits for the year, with 100.98 inches of rain, 31% above its year-to-date average.
“The trades have been there most of the month but it’s not been super wet. It’s been kind of what we were expecting,” Kodama said. “… The way drought manifests itself on the windward side of the Big Island, windward slopes, anyway, is you’ll get rain every day or almost every day. But it’s just that the amount of rain is lower than what you’d expect normally. And that’s what’s been occurring.”
And while most of East Hawaii has remained green, so far, other parts of the island are slipping into drought conditions. In his last drought statement, dated May 8, Kodama wrote “With the exception of the Kona slopes of the Big Island, leeward areas of the state may see increasing drought conditions during the summer.”
That assessment is borne out in the numbers.
The Waimea Plain gauge received just 0.91 inches for the month, just a third of its usual 2.61 inches, bringing it to 8.8% for the year, just 40% of its norm of 22.08 inches. And Honokaa also got about a third of its normal May rainfall, 2.3 inches, bringing its total for the year to 40.13 inches, almost 20% drier than normal.
“It’s been creeping along in leeward Kohala and up in the Pohakuloa region it’s been drying out,” Kodama said. “I just found out (Thursday) that even the Honokaa area is drying out. Parts of (Hawaii Volcanoes) National Park are getting dry, too — the windward side not so much, but more in the lee of Kilauea volcano it’s been drying out.
April 15, 2025
Does anyone have an historical record of annual rainfall in the Kona Coffee belt? I’m trying to see if volcanic haze from the 1983 and onward eruptive cycles coincides with reduced rainfall in that area. I used to work with Natural Resources Conservation Service as the District Conservationist in Kealakekua back in the late 90’s and it seems rainfall has been reduced in that are over several decades. I’d like to find some of the data from 1983 to current on annual precipitation along the Kona Coffee Belt.
April 21, 2025
Historical annual rainfall data for the Kona Coffee Belt from 1983 to the present can be challenging to find as a single, comprehensive dataset. However, here’s a breakdown of what information is available and how you can potentially access it:
1. General Rainfall Trends:
Kona Coffee Belt Rainfall: Greenwell Farms notes that the Kona Coffee Belt typically receives 70-plus inches of rainfall annually.
Shift in Rainfall: Some sources indicate a noticeable shift in rainfall patterns after 1983, coinciding with the start of Kilauea’s eruptive cycle. Konacoffee.com mentions that before 1983, the annual rainfall averaged 68 inches, but after 1983, it decreased to an average of 49 inches.
2. Impact of Volcanic Haze (Vog):
Volcanic Emissions and Vog: Kilauea’s volcanic activity releases gases like sulfur dioxide, forming volcanic smog or “vog”.
Vog and Rainfall: Some sources suggest that vog can potentially reduce rainfall. Kona Coffee & Tea says that anecdotal evidence from farmers suggests less rain when Kilauea is erupting. Hawaii Public Radio notes that a recent study found less rainfall on days with heavy vog around Kilauea. USGS Study: A USGS fact sheet notes that in drier conditions, like on the Kona coast, vog’s acid aerosols might impede raindrop formation, leading to decreased rainfall.
1. General Rainfall Trends:
The Kona Coffee Belt typically receives 70-plus inches of rainfall annually. Some sources indicate a noticeable shift in rainfall patterns after 1983, coinciding with the start of Kilauea’s eruptive cycle. Before 1983, annual rainfall averaged 68 inches, but after 1983, it decreased to an average of 49 inches.
2. Impact of Volcanic Haze (Vog):
Kilauea’s volcanic activity releases gases like sulfur dioxide, forming volcanic smog or “vog”. Vog can potentially reduce rainfall. Anecdotal evidence from farmers suggests less rain when Kilauea is erupting. A recent study found less rainfall on days with heavy vog around Kilauea.
In drier conditions, vog’s acid aerosols might impede raindrop formation, leading to decreased rainfall.
3. Accessing Data:
Recommendation:
Start by contacting the National Weather Service and NRCS for historical data. Explore university publications and reach out to the CTAHR Kona Research Station and local farms for more specific information. By combining these sources, the data needed for analysis may be available.
Steve, your experience at the “Natural Resources Conservation Service” will help you every step of the way to figuring out the conditions that could cause reduced rainfall!
Don’t let “retirement” keep you from exploring this fascinating topic and feel free to publish all of your deductions, regarding VOG induced reduced rainfall in Kona or elsewhere in Hawaii, here on the Hawaii-Agriculture.com website.