After a slow start to Hawaii’s wet season this month, forecasters project above-average rainfall from December through April, according to the National Oceanic and Atmospheric Administration.
NOAA predicts that La Nina — a complex weather pattern characterized by cooler-than-average ocean temperatures in the equatorial Pacific — is likely to emerge in the tropical Pacific by the end of November and last through spring.
“We’ve had a slow start to the wet season,” NOAA Senior Service Hydrologist Kevin Kodama said Thursday during weather officials’ annual rainy season outlook. “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.”
Kodama said Thursday that the state this year experienced its ninth-wettest dry season in the past three decades.
“That wasn’t quite where I was expecting in terms of the statistics, but you know, it is what it is,” Kodama said. “We had some curveballs thrown at us in terms of the rainfall, but we still ended up with significant dryness in parts of the state.”
Despite forecasts predicting below-average rainfall during this year’s dry season, most locations statewide experienced near- to above-average rainfall from May through September. Kodama explained that the “forecast error” was largely due to 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,” Kodama said.
The Kona-low storms in May brought high wind and heavy rain to Hawaii island.
In June a period of dryness set in, and drought conditions were reported statewide by late June. The drought spread and intensified through July and into mid-August.
In early August, severe drought conditions, classified as D2 on the U.S. Drought Monitor map, were present, with extreme drought — classified as D3 — affecting the leeward areas of Haleakala on Maui.
“And what that did was, in addition to the mainly agricultural impacts that we saw, we had some water impacts as well, especially for those on water catchments and who depend on surface water diversions, especially on Maui County,” Kodama said. “And then there was a significant increase in brush fire ignitions. Especially in July we saw quite a number of fire ignitions, including pretty serious fire in the leeward side of Kauai that caused quite a bit of concern.”
But in late August, Hurricane Hone delivered strong winds and heavy rain to Hawaii island. Several rain gauges along the windward and southeast-facing slopes of the Big Island reported two-day totals exceeding 20 inches.
When Hone passed just south of Hawaii island, it eased the drought on the leeward side of Maui and eliminated the drought on the island, particularly on the eastern and southeastern flanks.
As September rolled in, the land began to dry again, leading to drought conditions in Maui County, Kauai and the leeward parts of Oahu. But wet conditions throughout the month prevented the expansion of drought on the Windward side of Oahu and most of Hawaii island.
Kodama referred to November as the transition month for rainfall with La Nina in place.
Climate models favor a weak La Nina event, which could lead to more low-pressure systems around the state and increased leeward rainfall. In contrast, a moderate to strong La Nina event is associated with a higher probability of more tradewind days than usual during the wet season, focusing rainfall on the east-facing windward slopes.
The anticipated increase in leeward rain is expected to eliminate drought conditions by the end of the wet season in April, weather officials said. Other impacts could include a lower likelihood of giant surf events.
Additionally, the increased rainfall will promote more vegetation growth, significantly reducing the risk of wildfires during this time of year, officials said. But Kodama said, depending on the climate conditions, the increased vegetation also could dry in the summer, raising the risk of wildfires.
NOAA advised residents to take precautions to ensure safety during periods of heavy rain and potential flooding. Avoid driving on roads with fast-flowing water, and refrain from walking across flooded streams, officials warn.
With increased rainy weather expected to cause flooding and landslides, residents can anticipate longer travel times and potential road closures or detours. Drivers are encouraged to identify alternate routes ahead of time to avoid disruptions.
NOAA also emphasizes the importance of preparing for lightning strikes, which can lead to power outages. Residents are urged to remain indoors when possible, as lightning can occur even in areas where it is not raining.
In flood-prone areas, it is crucial for residents to have an evacuation plan in place in case floodwaters threaten their homes, officials said.
While rare, thunderstorms can produce damaging wind, large hail and even tornadoes. NOAA urged residents to stay informed of changing weather conditions, as forecasts might shift rapidly.
