2021-22 Wet Season Outlook Predicts La Nina Conditions Across Hawaiian Islands
October 16, 2021, 8:00 AM HST
* Updated October 15, 6:03 PM
Weather experts anticipate a moderate wet season as drought conditions continue to plague the Hawaiian Islands.
On Friday, Oct. 15, senior service hydrologist for the National Weather Service Kevin Kodama provided the stateʻs 2021-22 wet season outlook, as well as an overview of Hawaiʻi’s dry season.
“This is a time of year where you should be prepared for an uptick in rainfall,” Kodama said. “If you’re on the windward slopes, it’s going to be wet for you regardless.”
The National Oceanic Atmospheric Administration (NOAA) climate prediction center declared on Thursday, Oct. 14, La Niña has returned and they expect conditions to persist into spring 2022.
This is the second consecutive year the state is headed into La Niña conditions, which isn’t uncommon, Kodama said. La Niña is an anomalous cooling of the ocean near the equator. The intensity of the event is anticipated to be at a moderate level.
“The wet season is set to start off slow with below-average rainfall persistent throughout October and November,” Kodama said.
By the time January hits, Kodama said, weather model forecasts are showing wetter than normal conditions across the Hawaiian Islands, which are predicted to last through April 2022.
“If we do end up with a moderate, or even stronger, La Niña, weʻre looking at the potential of heavy rainfall mainly focused on the east-facing windward slopes, which is due to higher frequency and stronger trade winds,” Kodama said. “This also means leeward areas may end up with below average totals, especially in Maui County and the Big Island.”
Drought conditions could ease in Maui County and the Big Island. However, Kodama said if a moderate to strong La Niña persists, the dry conditions will make it through the end of the wet season, “which would be really bad news as we head into the next 2022 dry season.”
If it ends up being a weak event, Kodama said the state could get significant low pressure systems with more westerly and Kona winds that will get the rainfall into the leeward areas.
“But right now at least, it’s looking like a moderate event,” the hydrologist stated. “If you want wetter conditions, you’d rather have weaker La Niña conditions. If you get a strong to moderate La Niña with strong trade winds, we’re not going to get rain in the leeward areas.
Kodama said the state had an early start to the dry season, which runs from May to September. According to the data, this year was the stateʻs sixth driest season in the past 30 years.
“Once May rolled around, severe drought had already come in place on the Big Island along the leeward Kohala slopes,” Kodama said. “When we got into June, drought conditions quickly worsened.”
Conditions contributed to the historic Mana Road brush fire that ignited in late July and scorched 40,000 acres spanning the Hāmākua and South Kohala Districts within a week.
Drought conditions became pervasive in Maui and a few months later, in Oʻahu and Kauaʻi.
Kodama said the impacts of that blaze will linger for a while because there was so much damage to the soil. It is going to take a while for the grasses to regrow in the area. Additionally, there are already severe erosion issues going on within the burn scar, which creates an elevated risk for flash flooding because of the changes to the soil.
The Kona slopes has its wet season while everywhere else in the state is in a dry season.
The Kona slopes were one of the few locations statewide that received near to above average rainfall. Kodama said rainfall on the Kona side will taper off and won’t be quite as wet as they were earlier in the summer.
While Hilo has had significant rainfall the past weekend, Kodama said the area should be drying out, with models showing a significant dry signal into November, especially if the trade winds are low.