This year’s wet season in Hawaii started off slowly, but then the rain came with a vengeance — a so-called “Kona low” in early December brought as much as 14 inches over three days.

Stormy weather set in again around the New Year. And then, the spigot seemed to shut off.

Now, almost 80% of Hawaii is experiencing some level of drought, and the rest of the state is “abnormally dry.” As recently as Jan. 18, none of the state was in drought. It was a dramatic turnaround from a winter that started off with an epic downpour, and that was predicted to be wetter than usual because of the climate phenomenon known as La Nina.

Though climate researchers have not yet had the time to analyze the numbers and pinpoint the causes, the effects are already being felt, especially on the leeward sides of the islands, where almost all the moisture comes in the winter. The next month or so is predicted to be wetter than usual, but time is running out for leeward sides.

Parts of all the major islands are in “severe drought,” the second most severe of four categories. But with the rainy season near an end, the islands could all be facing the most severe stage of “exceptional drought,” said National Weather Service hydrologist Kevin Kodama.

“If things go the way they are, it won’t take long,” Kodama said.

For many Hawaii residents, the lack of rain has not created a major hardship. In fact, sunny days with winter’s lower temperatures can seem ideal. True, the ubiquitous winter rainbows have been scarcer. But atmospheric conditions have been more friendly to green flashes, when the sun’s rim briefly turns green as it sinks below the ocean, and fiery sunsets.

There’s nothing pleasing about the lack of rain, though, if you happen to be a rancher. Dry weather can force ranchers to cull their herds and pay more for feed, and this dry stretch is coming on the heels of another one last year.

“If things continue, we’ll probably be back in another drought emergency in 60 days,” James Robello, Maui County executive director for the U.S. Department of Agriculture Farm Service Agency, said last week.

So what’s going on in the skies?

Usually, La Ninas mean wetter winters for Hawaii. La Ninas, which alternate with El Ninos and have an array of complex effects around the globe, occur when surface sea temperatures near the equator fall below normal.

This winter, however, the expected La Nina pattern was disrupted when the jet stream set up shop north of the islands and sat there, Kodama said. Normally the jet stream is more like a garden hose flailing around, but this winter, it was remarkably stationary. And Hawaii remained on the dry side of the jet stream, cutting it off from rain-bearing storms.

“What’s weird is how persistent it’s been,” Kodama said.

The clear connection between La Ninas and wet winters in Hawaii may be breaking down, said Pao-Shin Chu, professor in the Department of Meteorology at the University of Hawaii Manoa and the state climatologist.

“We have global warming in the background,” he said. “This process can affect the existing relationship. Global warming can stir the pot.”

The problem, when it comes to rainfall, is that the wet season will soon come to a close. That happens with the strengthening of subtropical high pressure north of Hawaii, which jacks up the trade winds but also prevents northern latitude storms from dipping as far south as Hawaii. The windward sides of the islands can still get plenty of rain from the trade winds, but by the time that air rides over the mountains, most of the water has been squeezed out, leaving little to none for the leeward sides.

Of course, tropical storms or hurricanes in the summer and fall can bring moisture to any part of the islands. But even then, the rain might fall on only a narrow swath, Kodama said — not to mention bringing the danger of wind and flood damage.

The weather service is predicting a wetter-than-normal pattern in April, and more rain has fallen on the islands in the past week or so.

But after the long dry spell, ranchers on Maui were already contemplating action, Robello said. They may have to buy grass bales to feed livestock. Calves can weigh as much as 100 pounds less when they are sold, bringing in less money. Ranchers may cull their herds, and because of the overall decline in health, insemination rates drop, meaning fewer calves down the road, Robello said.

On Maui, axis deer, which unlike deer on the mainland feed mostly on grass, compete with livestock for forage. And they’re adept at jumping over fences, Robello said, so a green patch that a rancher had hoped to save to the lean days of August can get gobbled up.

The December deluge, meanwhile, did more damage than good, he said, with much of the water running off. The drier parts of Maui lack the infrastructure of weirs and dams needed to capture run-off from huge storms. “Our systems are not designed for that,” Robello said. 

An aerial survey in March of the ohia forest on Oahu showed the tree crowns looking less healthy than they had six months ago, when the canopy was lush and green, said Rob Hauff, state protection forester for the Department of Land and Natural Resources. The likely culprit, he said, is pests that find it easier to get a foothold when the trees are weakened by dry weather. 

Although the state has not surveyed them, naio trees on the Big Island are also susceptible to pests in drought, Hauff said. The state usually plants endangered species during the wet season when they have the best chance of thriving, he said, and though it’s too early to tell, the stretch of dry weather probably didn’t help.

Earlier this month, the State Commission on Water Resource Management advised Maui residents to reduce water use.

“Streams that are normally gushing with water are barely flowing,” the commission’s deputy Kaleo Manuel said in a press release, including some that were approaching the lowest flows ever recorded.

Water suppliers — especially those that depend on surface water rather than aquifers — also have felt the squeeze. On Maui, that means water customers in Upcountry, the central valley and West Maui. Residents were urged to stop watering landscaping and washing cars, and to take shorter showers and turn off the faucet while brushing teeth.

The commission also warned about the danger of wildfires.

Even on Oahu, whose water comes from an aquifer, the lack of rain is having an impact. The Board of Water Supply asked residents to cut water use by 10% after some of its wells showed an increase in chloride, which indicates stress on the water supply. Some of this resulted from BWS shutting down another well to avoid sucking in water contaminated by the Navy’s Red Hill fuel storage facility, but it was also because of low rainfall.

The National Drought Mitigation Center at the University of Nebraska-Lincoln offers a ground-level view of the season’s progress, with weather observers across the country reporting on local conditions.

“Had to irrigate all our subtropical landscaping this week except the lawn and grove of Podocarpus, which are managing to stay green from the occasional rain showers,” an observer from Honokaa on the Big Island reported March 19. “Most afternoons are overcast, but rarely do we get any rain out of the clouds.”

But recent days have offered some hope.

“Received some drenching rain over the past week, rejuvenating the lawn, trees and shrubs,” the same observer noted on Saturday. “New plantings are growing quickly.” Still, the observer noted, “Only a third the amount of rain we received last March.”

Less rain means fewer of Hawaii’s trademark rainbows, which are especially plentiful in the winter because of more moisture, but also because the sun traces a lower arc in the sky, said Steven Businger, professor of atmospheric sciences at UH Manoa. The critical angle is 42 degrees above the horizon.

“In the winter, you have a lot more time when the sun is below that critical angle,” he said.

But despite the rainbow drought, the winter has been marked by more than the normal number of fiery red sunsets and green flashes, he said, “providing the spiritual sustenance we all expect in Hawaii.”

Civil Beat’s coverage of climate change is supported by the Environmental Funders Group of the Hawaii Community Foundation, Marisla Fund of the Hawaii Community Foundation and the Frost Family Foundation.