Most Hawaii locations can expect above average rainfall during the wet season, which officially began Oct. 1 and runs through April.
That’s according to the National Oceanic and Atmospheric Administration’s Climate Prediction Center, which predicts current La Nina conditions — which means cooler than normal ocean temperatures near the equator — are likely to continue through spring.
“The (computer) models are showing October to start off drier than average, then transition in November, and then wetter-than-average conditions in the large scale starting in December and then continuing through April,” Kevin Kodama, senior hydrologist for the National Weather Service’s Honolulu bureau, said last week in an online media conference. “The strength of the La Nina can affect what the rainfall distribution will be during the wet season.
“So if we have a stronger La Nina event, then rainfall may favor the east-facing windward slopes — and that’s because with the stronger La Nina events, we can have a higher-than-normal trade wind frequency during the winter months. And if the La Nina is going to be on the weaker side, then we’ll be able to see more weather systems that could provide significant rainfall in the leeward areas.”
Kodama said previous La Nina events “have produced some pretty big rain events — especially, for instance in the Hilo area.”
“Back in 2008, we had a four-day 40 inches of rain, I believe, it was in the Hilo and Puna areas,” he said. “The La Nina can produce quite a bit of windward rainfall, but in leeward areas, (drought) can persist, especially if the La Nina remains too strong.”
According to Kodama, most Hawaii locations “had below average rainfall through the dry season” for the dry season, which ran from May to September, but Maui County was hit particularly hard.
“The leeward areas of Molokai and Maui … ended up with D3 conditions, with is the extreme drought category in the U.S. drought monitor map. And that has affected agriculture operations, especially the ranching sector, where pasture conditions are extremely bad,” he said.
The Big Island didn’t emerge completely unscathed by the dry season either, according to NWS’s most recent drought information statement, released by Kodama on Oct. 8.
“In the leeward Kohala area, forage production was down by at least 30 percent. Forage production was also significantly below normal in portions of the Ka‘u district. Pastures in parts of the Hamakua District were also extremely dry,” Kodama noted in the statement. “The dry vegetation also helped produce significant fires in the North Kohala, South Kohala, and Ka‘u Districts. Several thousand acres have been burned by these fires.”
“We may see some improvement in drought conditions; however, they may not completely go away by the end of April when the wet season ends,” Kodama said Friday.
According to Kodama, the lack of volcanic emissions into the atmosphere since the end of Kilauea volcano’s lower East Rift Zone eruption in 2018, could be a contributing factor in wetter-than-normal summers the last two years in the Kona coffee belt.
“On the Kona slopes of the Big Island, the summer season is their wet season. But if you look at this past May through September … they’ve had a very wet summer. In fact, Waiaha rain gauge has had close to double of their normal rainfall for this past summer.”
Waiaha had received 75.79 inches of rain for the year through September — as Kodama said, almost twice its year-to-date average. It’s by far the wettest spot among the four Kona coffee belt rain gauges, with Kealakekua and Honaunau at approximately 60 inches each, almost a third more rain than normal. Kainaliu, with 48 inches, measured four inches, or 8% above its norm for the first nine months.
“With the volcano continuing to be fairly quiet, it could help them with their rainfall on the Kona side,” Kodama said. “But they’re getting out of their normal wet season, so I think they may be looking forward to some drier conditions.”
Kodama said the La Nina has also contributed to a relatively quiet tropical cyclone season in the Central Pacific Basin.
“And that’s also affecting the Atlantic,” he said. “The Atlantic is usually opposite from the East Pacific and the Central Pacific, so the Atlantic has been very busy … in terms of the hurricane season.”
According to statistics, the dry season the island has just experienced is the 11th driest over the past three decades.
“It’s not even close to record breaking, by any means,” Kodama said. “However, I think there’s a couple of factors in play in the perception of the public. It’s the intensity of the drought late in the dry season. August and September were extremely dry, and I think that really stands out in people’s minds. And the other thing to remember is that in the last seven years, really we’ve had wetter conditions across the state during the dry season. So five of the last seven dry seasons have actually been fairly wet. It’s only two of the last seven, including this one, that have had drier-than-average conditions.”
Email John Burnett at jburnett@hawaiitribune-herald.com.