Already featuring three Category 5 hurricanes east of the international date line, the Pacific has been furiously cranking out storms since shortly after the season began May 15. Aletta formed on June 6, with Bud quickly spinning up three days later. Before long, a seemingly ceaseless barrage of storms blew up, largely dodging land save for a few brushes with coastal Mexico and Hawaii.
Added up, this season tops the charts as the most energetic on record. Meteorologists evaluate how busy the hurricane season is by relying on a metric ACE — Accumulated Cyclone Energy — a measure of the intensity and duration of all the storms that form. Climatologists keep a running tally of ACE throughout the season to see how it stacks up against those from the past.
The average season-to-date ACE for this time of year is 125.7 units. Through Oct. 23, storms had churned up a combined 311 units. That’s more than two and a half times the typical expectation. Even more staggering is the fact that no other season in recorded history has climbed above 295 units, reached in 1992. 2015 came in third place, at 287 ACE units. With five weeks left to go, we’re truly in uncharted territory.
The season featured many highlights, among them the distinction of being only the third eastern Pacific season to boast three Category 5s. Just Monday afternoon, Willa metastasized into a 160 mph beast.
Willa became the 10th major hurricane, Category 3 or higher, to form in the eastern Pacific this year. So far, 2018 is tied with 1992 for the second-most major hurricanes on record in this region.
While Willa poses a danger to Mexico, the other two Category 5s — Lane and Walaka — spent most of their destructive energy while whirling offshore. Walaka danced the Cat-5 tango with a typhoon of equal strength back on Oct. 2. Seven other storms achieved Category 4 status.
Three storms impacted Hawaii directly. Hector passed south of the Big Island in August, clipping the archipelago with squalls, light wind and rough surf. Then came Lane two weeks later, dropping 50 inches of rain and setting yet another statewide tropical cyclone rain record. Yet a third system — Olivia — brought flooding in mid-September, marking the first year on record when a trio of windstorms lashed the Aloha state. Research suggests that Hawaii will find itself in the crosshairs of more storms in the future, thanks to climate change.
That’s not the only clump of storms to wander in strange spots. The remnants of Rosa and Sergio passed over the desert Southwest — the former near tropical-storm strength. Rosa drenched Arizona in a widespread three-to-five inches of rain, causing mudflows and inundating roadways.
The dramatic boost in storminess is particularly surprising given the lack of an El Niño pattern. During an El Niño, somewhat westerly equatorial winds pile up warm water over the Eastern Pacific’s development region, often fueling storm growth.
“While there is a general view that El Niño increases Northeast Pacific hurricane activity, which is true, it doesn’t take a full-blown El Niño event to lead to a memorable season,” wrote Phil Klotzbach, a hurricane researcher at Colorado State University, in an email. “Neither this year nor 1992 met the official NOAA El Niño threshold criteria, but were still the most active northeast Pacific regions measured by ACE.”
Klotzbach points to anomalously warm sea surface temperatures — close to 2 to 4 degrees Fahrenheit above normal — as well as a reduction in wind shear across the Pacific’s hurricane hot spot. That means there’s less change in wind to tear apart developing storms, making it easier for them to form.
Similar conditions in the Atlantic contributed to our hellacious hurricane season last year. September 2017 proved to be the most vigorous month in recorded history for the Atlantic.
And water temperatures will continue to warm. The scientific consensus is that this will favor stronger storms in the years ahead.
But the sheer uptick in strength isn’t the only fingerprint of climate change. It seems nowadays that many storms catch forecasters off guard by rapidly intensifying. That means their winds strengthen at least 35 mph (30 knots) in 24 hours.
Brian McNoldy, a hurricane researcher at the University of Miami, said that of the dozen hurricanes in the eastern Pacific this season, 83 percent rapidly intensified at some point (compared to the historical average of 79 percent). In late August, McNoldy said, Hurricane Norman’s peak winds increased 80 mph (70 knots) in 24 hours, the most radical change of any eastern Pacific storm in 2018.
As the oceans warm, more storms will probably do this.
Willa, the latest eastern Pacific hurricane, went from a low-end tropical storm to a Category 5 in less than 48 hours. It has since weakened some to a Category 3, but is on a crash course with Mexico’s west coast.