The sun was still up Monday when the four-engine turbo prop plane made a pass through the eye wall of Hurricane Lane.

For meteorologist John Bravender, it was a first in-person glimpse of the kind of monsters he tries to measure, whose paths he aims to predict.

He witnessed the “stadium effect” — immense walls of clouds surrounding the eye, with clear blue sky above. He and the others on board were  jostled as the plane — a P-3 operated by the National Oceanic and Atmospheric Administration — hit the eye wall. The turbulence was severe enough that the plane had to miss a mission Tuesday morning as the ground crew made sure it was fit to fly.

Apart from the obvious wonders of flying through a Category 4 hurricane, Bravender was struck by how the air crew uses the predictions that he and his colleagues generate to determine where to fly and what to measure. And it was a chance to see how the data they depend upon is collected. The plane, for instance, releases “dropsondes” — cylinders holding monitoring equipment, floating by parachute into the hurricane.

Other planes, flying at much higher altitudes, survey the environment that the hurricane is moving toward to get a sense of how atmospheric forces will steer it or influence its intensity.

Data like that is used to predict the path of Hurricane Lane — a subject of intense interest for residents of Hawaii over the next few days.

A satellite image of Hurricane Lane on Tuedday. NASA

Only two weeks ago, Hurricane Hector passed safely to the south of the islands, as many hurricanes do. A strong ridge of high pressure to the north of Hawaii acted as a kind of brick wall, keeping the storm from wandering far enough north to do damage.

Lane appears to be different. A trough of low pressure to the west of Hawaii is generating higher-altitude winds out of the southwest expected to push the hurricane to the north, toward the islands.

Despite advances in dynamic prediction models, it’s challenging to predict the pivot point of a hurricane that’s turning course, said Bravender, warning coordination meteorologist at the Central Pacific Hurricane Center.

On the scale of the globe, the differences are not big. The models may only vary by a couple hundred miles. But out here in the middle of the Pacific, that difference “means day and night,” said Pao-Shin Chu, professor in the atmospheric sciences department at the University of Hawaii and the state climatologist.

Welcome to the “Cone of Uncertainty” —  not a philosophical work, a psychological condition or sci-fi headgear, but life on the Hawaiian Islands as Lane approaches.

The cone is the familiar image on television news screens and weather websites, illustrating the range of possible routes for a hurricane.

Lane’s cone is based on error rates in hurricane predictions over the past five years, Bravender said. As of Tuesday evening, the cone enveloped at least part of all of the islands.

Two of the most respected dynamic weather models, fed by vast amounts of real-time data, have come to different conclusions so far on Lane’s path. One has it blowing past slightly south of the islands, with effects still likely but no direct hit. The other has it veering more sharply to the north, close to the Big Island.

It’s impossible to say which model is more accurate. In any given storm, one model may outperform the others, but there’s no overall trend.

“If only there were a go-to model we could always follow,” Bravender said.

The course of Lane is not the only concern. One big question, as of Tuesday, was the effect of wind shear on weakening the storm.

The current path of Hurricane Lane as of 5 a.m. Wednesday, according to NOAA. 

Hurricanes are extremely tall structures. So when surface winds are blowing in a different direction than those higher up, the vertical structure can be torn apart, sapping the hurricane of strength. This can happen, for instance, when trade winds at the surface are blowing in a different direction than the jet stream higher up.

This is expected to happen to Lane.

The question is how quickly the hurricane will wane after its head is lopped off. When that happens, the remnant storm would be more susceptible to being pushed away from the islands by the trade winds, said Bob Farrell, a meteorologist and owner of Curlyweather in Pahoa.

Also, if the storm were to hit the big peaks of Mauna Loa and Mauna Kea on the Big Island, friction with the land could also diminish Lane’s strength, Chu said.

Lane’s menacing approach toward Hawaii is occurring against a backdrop of a spell of unusual weather, Farrell said. The subtropical ridge — that wall that often keeps storms from coming too far north — usually dominates all summer. But this year, weather systems from the northern latitudes have been weakening the wall.

This could be the result of the enormous amount of warm air in the Northern Hemisphere, Farrell said. This can create high pressure cells, such as along the West Coast of North America, interrupting the west-to-east flow of air and forcing the jet stream to curve farther south.

Chu also noted some unusual weather elsewhere. In the Western Pacific, for instance, typhoons have been tacking an unusual path toward Japan.

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