East Hawaii can likely expect above average rainfall this year, though drought conditions in some leeward areas of the island could persist or worsen.
The National Weather Service in Honolulu released its annual wet season rainfall outlook Tuesday, which showed current neutral conditions have a 55-60 percent chance of transitioning to a La Nina state — or cool phase — for Hawaii’s typically wet season, which runs from October-April.
A moderate to strong La Nina system is predicted to bring more rain to windward slopes but leave some leeward areas dry. Forecasters are unsure how strong this year’s La Nina will be. It’s predicted to stick around through the spring, when conditions should transition back to neutral.
“It depends on the strength of the La Nina,” said Kevin Kodama, a hydrologist with the National Weather Service, on Tuesday. “If it gets pretty strong — and we don’t know what the intensity will be — it becomes more likely leeward sections of the island could stay dry.”
The majority of Hawaii Island is under at least moderate drought, with some pockets in Ka‘u and South Kohala experiencing extreme drought. The rain gauge at Hilo International Airport recorded 57.53 inches of rain through September, or 64 percent of average for the year. Pahoa registered 54.59 inches, which is 56 percent of average, and South Point recorded just 8.19 inches through September, 34 percent of average. Waikoloa saw 4.34 inches through September, 47 percent of average for the year.
Some parts of West Hawaii saw a boost in rainfall in September, bringing year-to-date totals closer to normal: Kealakekua registered just more than 41 inches through September, or 90 percent of average, and Waiaha recorded 40.39 inches through September, 105 percent of its yearly average.
The Hilo airport has registered about 8 inches for October so far, Kodama said, but is still running about 32 inches below average for the year.
Last year, forecasters predicted a developing La Nina to bring near-normal to above-average rainfall for the wet season, but that proved “weak and short-lived and only lasted a few months,” Kodama said, and conditions overall were “very erratic.”
The year prior, strong El Nino conditions in the Pacific dragged rainfall totals below normal for most of 2016.
This year’s dry season, which ran from May-September, was drier than average — forecasters deemed it the 13th driest dry season in the past 30 years. Hawaii saw its wettest dry season in 30 years in 2015.
Unlike 2015 and 2016, this year’s hurricane season for Hawaii also has been quiet and has not brought a boost in rain during the typically dry months.
Email Kirsten Johnson at kjohnson@hawaiitribune-herald.com.
