at about this point, as Hurricane Norman was approaching Hawaii from the east, that forecasters were already predicting the cyclone would veer off to the north of the islands.
It’s not the same with Hurricane Olivia. The same atmospheric forces that ended up turning Norman are not there, forecasters said Friday.
“We hope Olivia turns away from the islands, but so far we are not seeing that,” said Robert Ballard, science and operations officer with the Central Pacific Hurricane Center. “It’s hard to believe we’re going through this again, but here we go.”
As of Friday evening all of the islands from Oahu to Hawaii were sitting within Olivia’s cone of uncertainty along the hurricane’s projected path.
“Chances are looking pretty good that the Hawaiian Islands will feel some impact,” Ballard said.
As of Friday night forecasters were predicting that Olivia will gradually weaken into a high-end tropical storm as it reaches the islands by the middle of the week.
But what kind of impact is the question. Forecasters were predicting further weakening due to marginally cooler waters, drier air and increasing southwesterly wind shear, but they weren’t sure about the intensity forecast.
Part of the uncertainty, they said, is due to the fact that Olivia is an annular hurricane, with a clearly defined eye surrounded by a tightly packed cloud core with little to no outer rain bands.
With the core insulated and protected from external influences, this type of hurricane often weakens more slowly than normal. So it’s possible Olivia won’t fade as much as some of the computer models suggest.
“It doesn’t mean it’s invincible, but it is more resistant,” Ballard said.
How much rain the islands receive is also uncertain. Because an annular hurricane has no outer bands, he said, it might lack the usual spread of rainfall.
On the other hand, the annular shape is often a temporary condition, so those swirling rain bands might still have a chance to spread.
While Olivia is likely to threaten the islands as a tropical storm, he said, it is certainly possible it could maintain its hurricane strength of 75 mph or greater.
“In general, it’s a very healthy-looking hurricane,” Ballard said. “Maybe it’s not as impressive as it once was, but it’s still going to be a pretty healthy system as it gets closer.”
Whether Olivia is a hurricane or a tropical storm, it might not matter. Another hurricane, Iselle, was downgraded to a tropical storm in August 2014 just before it made a direct hit on Hawaii island and caused nearly $80 million in damage.
Iselle was also considered an annular hurricane as it approached the islands.
Dennis Hwang, author of the Hawaii Coastal Hazard Mitigation Guidebook, was a member of a National Disaster Preparedness Training Center team that visited Puna to assess the damage following Iselle.
The team observed ruined shoreline roads, crippled roofs, hundreds of toppled albizia trees and damage from storm surge. Eyewitness accounts in Kapoho described the ocean water rising 6 to 8 feet and waves reaching up to a 16-foot deck.
Hwang said Oahu residents likely would be surprised by the punch of a high-end tropical storm.
“A tropical storm can cause a lot of tree damage. It doesn’t have to take a hurricane,” he said.
Mike Iwashita, staff meteorologist with UH’s National Disaster Preparedness Training Center, said last month’s serious threat from a menacing Hurricane Lane helped to increase disaster preparedness and resiliency on Oahu.
But, he conceded, there may be some who are suffering from hurricane fatigue and might ignore the danger.
“The consistent message is that the warnings should be taken seriously. They are not issued lightly,” Iwashita said.
Ballard said Olivia is approaching from the northeast, so windward sides of the islands should prepare for large surf and surge. Leeward sides can’t rest, however. Winds tends to accelerate downslope and through gaps in the mountains toward the lee sides, he said.
Monday may be the last day to prepare for Olivia, especially for those on the Big Island and Maui, he added.