Weather forecasters have high confidence Hurricane Flossie will take a track that will keep it well south of the Islands and spare the rest of the state after battering the Big Island with tropical-storm-force winds starting today.

Early predictions were that Maui, Honolulu and Kaua'i counties would experience winds of 25 mph or so, with gusts of 30 mph, along with an inch or two of rain, but not enough to cause significant flooding, said Jim Weyman, director of the Central Pacific Hurricane Center.

"We feel pretty confident about the track forecast," he said.

The predicted path, after taking the eye of the storm south of the Big Island, continues to the west-northwest, roughly parallel to, but farther south of, the rest of the state.

Flossie has quite closely followed the track predicted by the roughly 15 computerized models the National Weather Service uses.

"It's been fairly well-behaved as far as our track goes," said Ray Tanabe, warning coordination meteorologist with the National Weather Service in Honolulu.

And the models continue to agree on the path for the next several days, Weyman said.

Forecasting data is substantially more sophisticated today than it was 15 years ago for Hurricane Iniki, which caused $2.5 billion damage on Kaua'i and significant coastal damage elsewhere in the state, and 25 years ago for Hurricane Iwa, whose estimated damage on Kaua'i was $250 million.

Both Iwa and Iniki initially were south of the Islands, as Hurricane Flossie is. But then both of them turned north.

Tanabe said forecasters understand the conditions that led to that change of course, and they are quite different than the ones in place now. And that's why the National Weather Service seems secure that the hurricane is unlikely to make the same late beeline for the Islands.

Flossie has a powerful high-pressure area to the north of it. In the northern hemisphere, winds swirl clockwise around high pressure. This provides Flossie with a strong east-to-west wind at its back, which is "steering" the storm westward.

Neither Iwa nor Iniki had such a strong high-pressure system, so the steering winds were weaker.

Plus, in both the 1982 and 1992 hurricanes, there were strong low-pressure systems to the west of the Islands, which "produced a steering flow out of the south," Tanabe said.

Without a lot of strong wind behind them, when the two storms ran into the south winds, they turned right and hit Kaua'i.

That's the difference. The strong steering winds from the east, and the lack of a strong south wind, should push Hurricane Flossie past the Islands, meteorologists said. Similar conditions in July did the same with Tropical Depression Cosme.

HIGH CONFIDENCE LEVEL

While the weather service tracked both Iwa and Iniki as they approached the Islands, the agency never expressed the kind of confidence then that it did yesterday.

Iwa started as a tropical storm to the southwest of Kaua'i and gained strength as it moved north. It was being probed by Air Force reconnaissance aircraft as it came toward Kaua'i.

In those days before the Internet was commonplace, residents were warned primarily by radio and television, but it had been more than two decades since the last serious storm, and many were still out driving as power lines bounced like rubber bands between the wooden poles and sheets of roofing began flying through the air.

Iniki's approach had all of Hawai'i in a state of crisis. The National Weather Service, in a post-impact report, used the understated language: "The people of Hawai'i were sufficiently warned."

The storm moved up from the south, alternately aiming toward Kaua'i or at the channel between Kaua'i and O'ahu — potentially placing Honolulu at risk of hurricane-force winds. Ultimately, the eye of the storm passed directly over Kaua'i, creating a level of devastation so great that it took the island's economy a decade to recover.

Warning systems, as well as the amount of information available to the public, are significantly better today than during those storms — thanks largely to computerized weather models.

The models come in several different flavors, Tanabe said. Different agencies, within the U.S. and internationally, develop their own predictive models.

"They run on the same type of physics, but some tweak one factor or another differently," he said.

One class of models, statistical models, works primarily with existing statistics and climate data, studying things like what past hurricanes in a region have done. Another class, called dynamic models, takes into account weather features present in the region, like the strength and location of high- and low-pressure systems.

A third class, consensus models, combine the data from several other models and, in essence, averages their predictions.

MODELS IN AGREEMENT

When the weather service studies all its models, it can get wide variance, which forces meteorologists to try to understand what's causing the difference.

Or the models can agree, as they seem to be doing with Hurricane Flossie.

"The worst-case scenario is that they all agree but they're all wrong," Tanabe joked.

Another set of models looks at the strength of a tropical storm system, and uses things like water temperature, predicted path and the speed and direction of upper and lower-elevation winds to calculate the future strength of the hurricane. Flossie has been less well-behaved with respect to models in this arena, remaining powerful at the same time it has moved into cooler water, which was predicted to drain its wind speeds.

"Hurricane Flossie has been surprisingly resilient to cooler ocean temperatures so far," the weather service said in one of its online advisories yesterday.

But it seemed to weaken through the day yesterday. Weyman said satellite measurements suggest, for example, that the tops of Flossie's clouds were growing warmer. Since higher-elevation clouds are generally colder, that suggests the storm is shrinking vertically — getting shorter. And that means weaker.

"Also, the eye is not quite as dynamic as it was," he said. A distinct eye, with an eye wall that completely surrounds the hurricane's center, is an indication of a very powerful storm.

Weyman said forecasters have an additional tool for Flossie — storm-chasing aircraft that fly into the hurricane and make direct calculations of its wind speeds, temperatures, pressures and other factors. Weyman calls it "ground truth." It is information which, in the absence of the hurricane planes, must be estimated from satellite sensing data.

THE FAIRY-TALE FACTOR

Weyman said he gives regular talks on hurricanes, and frequently comes across popular myths about storms. One is that Kaua'i is more likely to be hit by a hurricane, and even that Kaua'i is the only island that can be hit by one. Both are wrong, he said.

"All the islands are at equal risk," he said. Two hurricanes in the past quarter-century have either hit or passed near Kaua'i. Either could have caused more significant damage on O'ahu with a change of less than 100 miles in their path, he said. Both Maui and the Big Island suffered severe damage from the Aug. 9, 1871, "Kohala Cyclone."

Another myth is that the mountains of the Big Island protect it from hurricanes.

Those mountains are little more than a "speed bump" to a hurricane," Weyman said. While they appear large to us, they represent only about 5 percent of the mass of a big hurricane and would have little impact on it, he said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.