From Hawaii to Mexico, powerful storms have buffeted a wide swath of the Pacific Ocean in 2018. Now, with Hurricane Willa bearing down on southwestern Mexico on October 23, the hurricane season across the central and eastern regions of the Pacific has become the most active on record — at least by one measure, known as accumulated cyclone energy.
So far in 2018, there have been 22 named storms in the central and eastern Pacific regions, including 11 major hurricanes of category 3 or stronger. The latest in that string of storms, Willa rapidly strengthened from a tropical storm on October 20 into a category 5 hurricane two days later.
Hurricane #Willa, seen by #GOESEast, is now a “potentially catastrophic” Cat. 5 storm. Willa is expected to make landfall along the southwestern coast of Mexico Tuesday afternoon or evening. Take a look at Willa’s path on our Pacific hurricane tracker: https://t.co/9aoFdvDmTr pic.twitter.com/nu2ChERXRd— NOAA Satellites (@NOAASatellites) October 22, 2018
At 2 p.m. EDT on October 23, as the storm approached the coast, it weakened into a category 3 hurricane, with maximum winds churning at 195 kilometers per hour.
The eastern Pacific season has been “very active,” says Gerry Bell, a research meteorologist at the National Oceanic and Atmospheric Administration’s Climate Prediction Center in College Park, Md. But whether or not the 2018 season is a record-breaker “depends on how you classify it,” Bell says.
The 2018 season in the eastern Pacific has already had the largest number of major hurricanes on record, he says. But there are many ways to measure the activity of a storm season: number of overall storms, number of named storms, number of major hurricanes above a category 3. To better compare the overall strength of the season with historical records, NOAA uses the accumulated cyclone energy, or ACE. ACE takes into account both the intensity and the duration of a season’s storms, says Bell, who developed the measure in the 1990s. A major hurricane that lasts only a few days, for example, would add less to the overall energy of the season than one that lasts for more than a week.
Meteorologists also separate the central and eastern Pacific into two distinct basins, with the dividing line at 140° W longitude, east of Hawaii. The two basins have different hurricane season lengths: Both end on November 30, but the eastern Pacific season begins in mid-May, while the central Pacific season starts June 1.
Counted alone using the ACE measure, the eastern Pacific season is currently the third most active on record — and there’s still a month to go, Bell notes. “It’s not uncommon at all to have late October hurricanes. Back in 2015, there were three late in the season, including Hurricane Patricia.” Patricia, with sustained winds of 338 kilometers per hour, remains the strongest recorded storm for the region.
Taking the storm power of both regions into account, though, shows that the accumulated cyclone energy of the central and eastern Pacific hurricanes unleashed a record-breaking year. Combining the tally may make sense: Storms often take long westward journeys across the 140° boundary line, particularly during the peak of the season between July and September. Four named storms made that trek in 2018, including Tropical Storm Olivia, which hit Hawaii on September 13.