Hurricane season breezes by Hawaii

The 2020 hurricane season is drawing to a close in the Atlantic with a record- breaking 30 named storms — 12 of which made landfall on the mainland.

The Central Pacific?

We had two storms — an early tropical depression that didn’t come anywhere near Hawaii, and Hurricane Douglas, which passed uncomfortably close to the islands in late July but produced little impact.

It was a below-average season for the Central Pacific basin, which extends north of the equator from 140 degrees west to the international dateline (180 degrees). The basin sees four to five tropical cyclones during an average season, which runs from June 1 to Nov. 30.

In May the Central Pacific Hurricane Center in Honolulu released its annual hurricane season outlook calling for two to six tropical cyclones, with a 75% chance of near- to below- normal tropical cyclone activity and a 25% chance of above-normal activity.

The season started with neutral El Nino conditions in the equatorial Pacific, but it transitioned to La Nina with equatorial ocean temperatures steadily cooling in the summer.

“That quietness in the Central Pacific is pretty typical for a La Nina season,” said Phil Klotzbach, a hurricane researcher at Colorado State University.

Generally, the large-scale circulation during La Nina is characterized by a large-scale sinking motion of air over the Eastern and Central Pacific, which tends to suppress hurricane activity, Klotzbach said.

There were a lot of positive outgoing long-wave radiation anomalies, which implies less cloudiness and a more stable atmosphere that also helps to suppress hurricane development, he said.

While La Nina generally suggests a quieter hurricane season in Central Pacific, it usually means the opposite for the Atlantic. And that was certainly the case this year.

Overall, the 2020 season in the Atlantic produced 30 named storms with top wind speeds of 39 mph or more. Thirteen of the storms became hurricanes (top winds of 74 mph or greater), including six major hurricanes (top winds of 111 mph or greater).

According to the National Weather Service, the Atlantic season saw the most storms on record, surpassing 2005 with 28 storms. It also produced the second- highest number of hurricanes on record.

In the Central Pacific, Boris was the first cyclone of the season, moving into the basin from the east as a tropical depression on June 27. The former tropical storm weakened to a remnant low the next day.

Boris was only the second tropical cyclone to occur during June in the Central Pacific since 1950 and the first since Tropical Storm Barbara in 2001, weather officials said.

The early arrival led some to conclude the Central Pacific was in for a busy season, but the next storm didn’t show up for nearly a month.

Hurricane Douglas burst into the Central Pacific basin on July 24 as a Category 4 major hurricane with maximum sustained wind of 130 mph. Douglas, guided by a ridge of high pressure, churned toward Hawaii, and government officials warned islanders to prepare for the worst. But the storm gradually weakened and passed within 30 miles north of Oahu on July 26 as a Category 1 hurricane.

Forecasters said a weakness in the ridge aloft and increasing vertical wind shear, mainly at higher levels, likely caused the hurricane to jog northward just as it was tracking toward Oahu.

Douglas’ most damaging wind and rain bands lashed out farthest to the north and west, away from the island, while tropical storm-force winds came within 10 miles of Oahu, satellite, radar and aircraft reconnaissance data indicated.

“We were lucky,” hurricane center meteorologist John Bravender said afterward. “If there was only a slight shift southward, it would have brought significant damaging winds and rains.”

Bravender said it was the closest a hurricane had come to Oahu since before Hurricane Dot, which passed about 60 miles southwest of the Waianae Coast before making landfall on Kauai in August 1959.

As it turns out, Douglas was the last hurrah for the 2020 season, as August and September — historically the busiest months for hurricanes — were quiet.

Douglas was the season’s only storm powerful enough to generate what is called accumulated cyclone energy, or ACE, a metric of storm intensity and duration. Klotzbach said Douglas generated an ACE number of 12, resulting in a second straight year of below-average cyclone energy in the region (last year’s ACE was 14).

The average Central Pacific hurricane season produced 18 ACE, he said.

While hurricane season might officially end today, meteorologists say it is possible for tropical storms to develop during any month of the year.