A wetter-than-usual rainy season is being forecast by the federal government’s weather watchers.
The wet season for most of Hawaii began Oct. 1 and runs through April 2025.
“We’ve had a slow start to the wet season,” Kevin Kodama, senior service hydrologist for the National Weather Service in Honolulu, said during a press conference Thursday. “October has been fairly dry across most of the state. But the climate model consensus does favor wetter-than-average conditions, especially starting from December and continuing on through April of next year, (with) November being kind of a transition month in terms of rainfall.”
According to Kodama, the National Oceanic and Atmospheric Administration’s Climate Prediction Center is predicting a La Nina weather pattern “to emerge in the tropical Pacific by the end of November and … to persist until spring of next year.”
A La Nina pattern occurs when trade winds shift, blowing warmer waters toward Asia. This then allows colder water to rise to the surface of the ocean.
“The probabilities coming from the climate models favor a weak La Nina event,” Kodama said. “And so, the effect is that with both windward and leeward rainfall enhanced, we’re expecting … drought conditions to be completely eliminated by the end of the wet season in April. Some other impacts would be lower likelihood of giant surf events.
“And with the enhanced rainfall and the reduction of dry forage and more growth in the vegetation, that greatly reduces the chance of wildfires during this time of year, which is a good thing. On the bad side, looking way down the line, perhaps next summer with the increase in fuel loads … there may be more risk for wildfires.”
Portions of Hawaii Island were under a Red Flag Warning as recently as Wednesday, which means that due to strong winds, low relative humidity, dry conditions and warm weather, the risk is high for fires to quickly spread out of control.
A Red Flag Warning was in place on Aug. 8, 2023, when wildfires decimated much of Lahaina, Maui, killing more than 100 people. In West Hawaii, seven structures were destroyed by fire that same day, as firefighters battled not only the blazes, but the winds gusting to 80 mph that caused the fires to rapidly spread.
One area that has its dry season when the rest of the state is experiencing its rainy season is the Kona coffee belt, which also has its rainy season between May and October.
“I would anticipate, with a weak La Nina event … they would tend to have enhanced rainfall on the Kona side of the Big Island,” Kodama said.
The forecast for an above-average wet season follows a dry season that was wetter than expected by forecasters.
“Most locations had near- to above-average rainfall. Unfortunately, that’s not what the forecast called for,” Kodama noted. “We forecast for below-average rainfall at the start of the dry season, back in May. And there are a couple of reasons for that forecast error, I guess you could say. One was that the wet season had an extension. We had a late start to the dry season. We had the latest kona low in at least 20 years, so that brought a fair amount of rainfall to the state.
“Then, later on in August, we had Hurricane Hone. We can’t see that far in advance, but that did have a significant impact, in terms of rainfall, across the state of Hawaii.”
At the end of September, Hilo International Airport had received just under 75 inches of rain for the year, 90% of its average. Mountain View had 120.72 inches, 96% of norm, while Pahoa measured 88.89 inches, 91% of its average rainfall.
On the leeward side of the island, always arid Kona International Airport had received 7.35 inches of through September, slightly above its average. Puuanahulu, in upslope North Kona, reported 10.81 inches of rainfall, just above half its year-to-date norm.
In the Kona coffee belt, four gauges all tallied average to above-average totals. Waiaha was the rainiest, with 55.19 inches, followed by Kealakekua with 50.8 inches, Honaunau with 48.71 inches, and Kainaliu with 44.15 inches.
The Ka‘u coffee regions also had received above-average rainfall for the first nine months of the year. Kapapala reported 53.42 inches, 144% of normal, while Pahala was close behind with 51.8 inches, 135% of its year-to-date average.
Dry months in June and July had caused drought conditions on portions of the Hawaii Island, especially in the island’s center along the Daniel K. Inouye Highway, but rainfall from outer rain belts as Hone passed to the south on Aug. 24 and 25 “eliminated drought on the Big Island,” according to Kodama.
“The Big Island got quite a bit of rainfall, 20 to over 30 inches of rain, especially on the east and the southeastern flanks of the island,” he said.
“…We ended up with the ninth-wettest dry season in the last 30 years.”
Email John Burnett at jburnett@hawaiitribune-herald.com.