Expect another active hurricane season

Don’t let your hurricane insurance lapse just yet.

It looks like Hawaii could experience yet another above-average hurricane season despite the ongoing decline in the powerful El Nino weather pattern.

Scientists say conditions during the June-through-November hurricane season are expected to be ideal for tropical storm formation in the ocean off Mexico, thanks to the discharge of El Nino-fueled ocean heat in that region.

That means Hawaii will have to be wary of the potential of more storms forming and tracking westward from that area, they said.

Tropical Storm Iselle, which slammed into Hawaii island in 2014 and caused tens of millions of dollars in damage, and many other powerful cyclones that threatened the islands, including hurricanes Guillermo, Hilda, Ignacio and Jimena last year, are examples of storms that originated from that area.

“We’re going to have to keep our eyes open,” said Hawaii state climatologist Pao-Shin Chu.

The Central Pacific sees four to five named tropical storms in a typical year, but last year one of the strongest El Ninos on record helped to generate 14 named storms, including eight hurricanes, five of which became major hurricanes. It was the most active season since reliable record keeping began in 1971.

The enhanced potential for a killer tropical storm aside, the weather over the next year could be pretty nice in contrast to some of the extreme El Nino anomalies seen over the past year, including oppressive heat and humidity, feeble tradewinds and winter drought.

That’s because the strong El Nino is rapidly weakening, and climate officials say there’s an excellent chance it will transition into its polar opposite, a strong La Nina, which could bring ample tradewinds and cooler ocean water, both of which could support seasonably cooler temperatures.

Research published last year by Chu and colleagues revealed that La Nina has been bringing less-than-normal rainfall to Hawaii in recent decades due to changes in large-scale atmospheric circulation patterns.

But Chu said that with this year’s powerful La Nina expected to wield more clout over the weather, the islands could see normal or above-average amounts of winter rain.

The National Weather Service’s Climate Prediction Center has issued a La Nina watch, saying there’s a 70 percent chance La Nina will develop in the coming months.

Officials say El Nino is likely to turn neutral by late spring or early summer and then transition into La Nina just in time to moderate Hawaii’s hottest months in the late summer and early fall.

“A strong La Nina is a good sign for us,” said Chu, a meteorology professor at the University of Hawaii at Manoa. “We need some rainfall and cooler temperatures.”

In the meantime Hawaii’s current drought is expected to continue well into the usual summer dry season, especially on the hard-hit leeward sides of the islands.

“The outlook is not good for the leeward areas,” said Kevin Kodama, hydrologist with the National Weather Service in Honolulu.

West Hawaii, in particular, is suffering severe drought with a few areas of the Big Island, namely Kona and Kau, experiencing an even greater level of dryness — described in the latest Hawaii Drought Monitor as “extreme drought.”

In a recent National Weather Service report, Kodama wrote that farmers on the Kona slopes are saying conditions are the worst in recent memory, even including 2010, which was a significant drought year for the area, and that this year’s crop will be affected.

In addition, several ranchers are reporting the loss of cows due to the drought and are reducing the size of their herds, he said. Moreover, wild pigs and goats have been moving onto ranchlands in search of water and causing damage to fences.

A fire season that started early in Hawaii this year is especially dangerous right now, officials said, because the El Nino-powered storms that made the 2015 dry season the wettest in 30 years created lots of brush that subsequently turned into fuel ready for burning.

The windward sides of the islands, meanwhile, are already seeing some tradewinds and moisture, Kodama said, so they are in good shape heading into summer.

Kodama added that as El Nino transitions into the neutral phase, forecasting weather trends becomes tricky. Generally speaking, the neutral phase offers normal conditions with equal chances of above- or below-average temperatures and rainfall.

How a greater chance of tropical storms affects the summer and fall climate remains to be seen.

But the hurricane threat is real, said Axel Timmermann, UH oceanography professor. He explained that the demise of an El Nino causes subsurface ocean heat to be pushed away from the equator into off-equatorial regions. There, he said, it weakens a feature known as the “thermocline ridge.”

The thermocline ridge is a relatively narrow region in the northeastern tropical Pacific where cold subsurface water is located right beneath the warm surface waters. This band serves under normal conditions as a natural break for hurricane genesis and development in the eastern tropical Pacific, the professor said.

According to research published in 2014 by UH scientists Fei-Fei Jin and Julien Boucharel, the residual heat from a strong El Nino event can destroy this natural break, leading to a greater chance for hurricane intensification in that part of the tropical Pacific compared with normal conditions.

“So this is certainly a process that needs to be closely monitored over the next months,” Timmermann said.

Timmermann, who works in the International Pacific Research Center at UH’s School of Ocean and Earth Science and Technology, said strong global signals point to El Nino backing off and La Nina kicking in over the coming months.

Timmermann said the decaying El Nino is notorious for causing extreme low sea levels in the ocean around Samoa, which causes a phenomenon known as “taimasa” — the massive coral die-offs of shallow reefs that get exposed frequently or permanently to air.

“This is happening right now and is likely to continue for several more months,” he said.

El Nino, which occurs every two to seven years and affects weather patterns around the world, is linked to warming at the equatorial central and eastern Pacific. La Nina, by contrast, is associated with lower-than-normal water temperatures in the same waters.

La Nina, which typically lasts up to a year, does not always immediately follow an El Nino, but research indicates that strong El Ninos are more likely to bring on La Ninas.

Also during La Nina, according to Timmermann, warming occurs in the western tropical Pacific, which can cause coral bleaching in many regions, including Australia’s Great Barrier Reef and the Coral Triangle near Indonesia and New Guinea.