KAILUA-KONA — Wet season is descending upon Hawaii Island, but there are a few spots in West Hawaii that might miss out on some much needed precipitation.
The National Oceanic and Atmospheric Administration released its wet season outlook Tuesday, forecasting a 55-60 percent chance of transitioning to a La Nina state for Hawaii’s typically wet season, which runs from October-April.
The amount of rainfall the leeward side of the island sees in coming months will depend heavily on the strength of La Nina, should it make an appearance.
“It’s looking pretty good it will develop,” said Kevin Kodama, NOAA senior hydrologist. “If it stays weak, there’s a better chance for Kona to get rainfall during the winter time.”
As the wet season approaches for most of Hawaii Island, the dry season will simultaneously descend across the Kona coffee belt — an elevated swath of West Hawaii where the rainy and dry seasons rotate inversely compared to the rest of the state.
September was wet almost across the board in West Hawaii, particularly in this unique area where rain gauges measured above average rainfall in areas like Kaloko, Kealakekua, which registered just more than 41 inches through September, or 90 percent of average, and Waiaha, which recorded 40.39 inches through September, 105 percent of its yearly average..
Rainfall in North and South Kona has been consistent enough to set it apart from the rest of the island, not to mention most of the state, almost all of which suffered through drought conditions in September.
While Kona hasn’t struggled with drought, other leeward areas have had significant problems that stretch back well beyond September.
Kodama said Ka’u and South Kohala, above the Waikoloa area, are specifically vulnerable, adding while there has been some spotty rain in these places, the rainfall trends have simply “been weird.”
The rain gauge at South Point recorded just 8.19 inches through September, 34 percent of average, while Waikoloa saw 4.34 inches through September, 47 percent of average for the year.
In these regions, brush fires are of particular concern.
“That (area) above Waikoloa is really dry, but maybe it’s so bad that the brush fire risk may be low because there’s nothing left to burn anymore,” Kodama said. “You can go past your risk phase and actually the risk level goes down because it’s so dry that even the (grass) is gone.”
He said he doesn’t know if the region has reached that point, but that the situation on the South Kohala slope is “pretty bad.” He added even a big storm or two won’t do the trick — not in Kohala or Ka’u.
“They’re in such bad shape right now that even if you do get some rain events, it’s going to take multiple rain events and not just one big one or a couple big ones,” Kodama explained. “You need good soaking rain to replenish that soil moisture so that it’s actually useful.”
Events that produce torrential rain often result in a substantial amount of runoff, even in areas with a solid watershed, which is absent throughout parts of South Kohala.
Still, the forecast is for a rainier season than normal in most regions across Hawaii Island.
Windward slopes didn’t get as much rain as initially projected during the recently ended dry season and “below average tropical cyclone activity” also mitigated precipitation totals in East Hawaii.
NOAA’s outlook predicts this year’s wet season will allow for a “probable” recovery from drought conditions across the Big Island’s windward side.
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 last 30 years. Hawaii saw its wettest dry season in 30 years in 2015.
Hawaii Tribune-Herald reporter Kirsten Johnson contributed to this report.