After Olivia we might get a 2-week break

First there was Hector, followed by Lane. Next it was Miriam, with Norman on her heels. Olivia is on the horizon and appearing to threaten the islands next week.

It’s been a busy month for the Central Pacific Hurricane Center, which since Aug. 6 has tracked three major hurricanes (Category 3 to 5) and another that reached Category 2 status.

With signs of a developing El Nino, it’s possible the parade of tropical cyclones marching across the Pacific will continue for the next couple of months and maybe even late into the hurricane season.

But one hurricane expert says we might be in for a break after Olivia passes — at least for a few weeks.

“Sub-seasonal variability should be working to suppress hurricane activity in your part of the world for the next couple of weeks,” Colorado State University hurricane researcher Phil Klotzbach said Thursday.

That variability, he said, comes in the form of the Madden-Julian oscillation, a pattern of tropical disturbance that circles the globe every 30 to 60 days and interrupts the norms of large-scale climate conditions such as El Nino.

The same variability, Klotzbach said, has started affecting the Atlantic hurricane season in the opposite way — with cyclone activity starting to pick up after an extended early-season lull.

“There would certainly be the potential for a re- invigoration of the North Central Pacific hurricane season in late September, but I would say after Olivia, it looks to be quieter at least through mid-September,” he said.

Why has the past month been so busy for tropical cyclone activity in the Pacific?

One reason is warmer- than-normal sea surface temperatures.

“They’ve been really, really warm in the tropical belt of the North East Pacific and the Central Pacific,” said Pao-Shin Chu, University of Hawaii meteorology professor and state climatologist.

Large expanses of the Pacific have been 1 to 1.5 degrees above their average temperature in recent weeks, Chu said.

“It provides lots of fuel for hurricanes to intensify,” he said.

Another reason is a general reduction in vertical wind shear across the Central Pacific basin, Klotzbach said.

Wind shear is the changing direction of the wind’s speed or direction aloft over a short distance within the atmosphere. When these winds aren’t strong, hurricanes are more apt to intensify and wander from the hotbed of tropical storm genesis off Mexico and Central America and into the Central Pacific.

Klotzbach said Madden- Julian oscillation (MJO) drives shorter-term alterations in vertical motion and vertical wind shear.

“While vertical wind shear has been below- normal for the past few weeks, the current phases of the MJO will likely drive above-normal shear in the Central Pacific — at least in the short term,” he said.

It was the strong southwesterly wind shear that was credited for slowing down powerful Hurricane Lane and then tearing it apart before it had a chance to unleash its power on Oahu.

“By and large, most hurricanes approaching Hawaii in the Central Pacific end up weakening because of wind shear,” said Steven Businger, professor and chairman of the UH Atmospheric Sciences Department.

Businger said a global- scale tropical atmospheric circulation known as the Hadley Cell keeps wind shear blowing and protecting the islands 9 out of every 10 days.

But times are changing, he said, and global warming is driving storms all over the globe on more northerly tracks and with greater intensity. What that means, Businger said, is that hurricanes that previously passed south of Hawaii are now drawing closer to the islands.

A number of studies predict that the Central Pacific will see more hurricanes, stronger storms and ones that intensify faster.

“We dodged a bullet with Hurricane Lane,” Chu said. “There could have been many billions of dollars of damage on Oahu. All those expensive houses on the south shore of the island — I’m not sure they were ready to face a Category 3 hurricane.”

Meanwhile, El Nino is expected to take hold soon. According to the National Weather Service’s Climate Prediction Center, the majority of long-range statistical and dynamic models forecast El Nino to develop in the equatorial Pacific sometime between September and November.

In its Sept. 3 update, the center said westerly wind deviations have become more prevalent over the western and east-central equatorial Pacific Ocean since mid-July.

And during the last four weeks, equatorial waters were mostly near average temperature across the east-central Pacific while remaining above average in the Central Pacific.

In El Nino years, Hawaii typically experiences more tropical storms, added summer heat and humidity, feeble tradewinds and winter drought, among other anomalies.

At the beginning of the hurricane season, the Central Pacific Hurricane Center predicted an 80 percent chance of near- or above-normal tropical cyclone activity. And, they said, if El Nino develops, the activity could be nearer to the higher end of the predicted range.