Monday | March 27, 2017
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Sheltered from the storm? Iselle debunks myths of an impervious island

Crouched in the shadow of two massive volcanoes, West Hawaii was spared most of the battering effects of Tropical Storm Iselle. But it won’t always be that way, and those who hold to the belief the island will always shelter them are making a mistake, National Weather Service officials say.

“Iselle should be an eye opener for everyone in the state, especially the Big Island,” said Robert Ballard, science and operations officer with the National Weather Service in Honolulu.

When Iselle slammed squarely into the southeast flank of Mauna Loa, it effectively debunked the myth that the Big Island has the power to deflect storms, Ballard said.

“We know the island has been hit directly in the past, and that’s what happened this time,” he said.

Mauna Loa and Mauna Kea, lauded though they are by some for their power to send storms glancing past the island, were no favor to Puna, where the eye of Iselle came ashore.

“We didn’t see any significant deflecting effect,” Ballard said “Iselle slowed down, but it passed right over the island. When it slowed down it made it even worse; it kept the center over the water longer, and it kept the rain and strong winds over the island longer. That’s not a good thing.”

The Puna region was stung with winds in excess of 60 mph, and hurricane-force gusts. Up to 15 inches of rain saturated some areas. In the leeward town of Captain Cook, light rain fell and breezes stirred. A ragged white wind line of capillary waves could be seen as the storm passed to sea, but close to shore, the water was calm.

The friction of the lower part of the storm circulating on land kept the base of the cyclone in place while the top of Iselle continued on, said Mike Cantin, a former warning coordination meteorologist with the Central Pacific Hurricane Center.

“The lower part of the storm was trying to push against a wall,” Cantin said. “It oozed out to the south and the top went over the mountains. That weakened it dramatically. Cyclones like to be vertically stacked.”

The mountains also effectively wrung the moisture out of the system, said Lt. Col. Jon Talbot, chief weather officer with the 53rd Weather Reconnaissance Squadron. The Hurricane Hunters flew into Iselle just before it made landfall.

“You got peaks more than 13,000 feet and an island 60 miles wide. That has a profound effect on wind circulation,” he said by phone from Mississippi. “Iselle was a jumbled mess when it got out the other side and it never got its act together.”

In Kona, more than 200 people rolled out sleeping bags at two hurricane shelters and waited for the rattling of wind that never came.

It could easily have been otherwise.

“If that storm came in from the southwest, it would have been an entirely different story,” Talbot said.

While forecasters had a good fix on Iselle’s track, no one knew exactly what impacts would occur where.

“This is the first time we’ve had a record of this since 1871 on the Big Island,” said Cantin, who was temporarily flown back to his old job as Hawaii faced the double threat of Iselle and Hurricane Julio.

Even as Iselle impacted Puna, it was somehow able to create 80 to 100 mph winds in upcountry Maui in the lee of Haleakala, trashing a vineyard and knocking down more than 100 trees at Ulupalakua Ranch.

These types of anomalies — funneling and downslope acceleration and other effects far from the eye — are poorly understood and hard to predict, Ballard said. They are reasons leeward Hawaii Island should never stop preparing.

“Every system is different,” Ballard said. “They’re such rare events that you don’t get much chance to learn. … We suspected the island terrain would tear Iselle apart pretty well, but until we saw it, we weren’t sure how much.”

There are other misconceptions circulating about hurricanes. One of them is the idea that the water around the island is too cold to support the systems, Ballard said.

“It’s too cold to develop a hurricane but it’s warm enough to maintain one,” Ballard said. “A cyclone isn’t necessarily going to weaken if that wind shear isn’t there.”

Strong upper-level wind shear over Hawaii tends to rip the top off of storms. About the time Iselle arrived, those winds weren’t very strong, which worried forecasters.

Absent the shear to eat at the system and shred it, the cyclone would just keep trucking along, Ballard said.

“If this breaks a few myths, and people prepare more, that might be the silver lining,” Ballard said. “The reality is that everyone needs to prepare when we say a hurricane is coming.”

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