Under normal circumstances, a quiet Atlantic hurricane season would be a safe bet this year: The global climate pattern known as El Niño is fast developing, and it’s known to diminish tropical cyclone activity in the Atlantic basin. But unusually warm waters — in some areas setting records for this time of year — could cancel that out, creating conditions that could instead fuel an active season of revved-up storms.
That means the outlook for tropical cyclone risks is significantly more complicated at the start of this year’s season that began June 1. National Oceanic and Atmospheric Administration scientists are expected to factor that uncertainty heavily into a hurricane season forecast that will be released Thursday.
Seasonal forecasting is always difficult, but it’s even harder to predict which of the competing influences will win out in the months ahead.
“There’s not a lot of historic precedence for this,” said Philip Klotzbach, lead hurricane researcher at Colorado State University.
As the season plays out against the backdrop of global warming — which has driven a flurry of storms that intensify quickly into devastating hurricanes — meteorologists remind people that it only takes one extreme storm to turn even a quiet season catastrophic.
People sift through the destruction left by Hurricane Dorian in the Mudd neighborhood of Marsh Harbour, Bahamas, on Sept. 7, 2019. The storm made landfall on the island as a Category 5 hurricane. Carolyn Van Houten/The Washington Post
Unusual ocean warmth raises storm risks
Hurricane season is set to begin with an already established trend of ocean warming that has been building since early March. By the heart of hurricane season in late summer and early fall, waters around the Caribbean, Gulf of Mexico and Southeast U.S. coast are always bathwater-like. That warmth could be especially pronounced this year.
“Those warm anomalies should, if anything, get stronger,” Klotzbach said.
That is bad news for hurricane risks. Warm water is a necessary ingredient for tropical cyclones, and the warmer the water, the greater the potential for extremely strong hurricanes. The warmth translates to increased moisture in the air and greater available energy for a storm to unleash.
And the recent ocean warming is grabbing climate scientists’ attention because of both its timing and its widespread appearance.
It’s normal for ocean temperatures to rise along the surface of parts of the central and eastern Pacific when El Niño develops — something scientists have been observing off the western coast of South America in recent months. Those changes in sea surface temperatures and in winds across the Pacific have domino effects around the world and can trigger weather extremes.
But the ocean warming observed as of late has developed in areas besides those Pacific hot spots — including parts of the Atlantic key for hurricane development. The deep tropics between the Caribbean and West Africa are significantly warmer than normal, something that could encourage any atmospheric disturbances moving into the Atlantic from Africa to organize and strengthen into tropical cyclones, said Brian McNoldy, senior research associate at the University of Miami and hurricane expert for Capital Weather Gang.
“When waves come off of Africa, if they get that kick right away, that might help them form a little quicker,” McNoldy said.
And though El Niño is known for accelerating planetary warming, the ocean trends are appearing well ahead of the climate pattern shift. Climate scientists don’t expect El Niño to arrive in earnest until some time in the coming weeks or months.
El Niño’s influence adds uncertainty
The ocean warmth notwithstanding, El Niño typically brings meteorologists a modicum of confidence in a quieter-than-average Atlantic hurricane season. It’s part of the cascade of impacts El Niño can have on weather patterns around the world.
El Niño is associated with towering clouds and a rising motion in the lower atmosphere over the central and eastern Pacific, something that changes atmospheric circulation patterns in a way that tends to send dry, sinking air over the central Atlantic. That means diminished activity in the tropical zones key for cyclone formation and development.
The circulation patterns associated with El Niño also tend to bring an increase in wind shear, or a contrast in wind speeds and direction at different altitudes, over the Atlantic. High wind shear makes it difficult for storm systems to organize into classic cyclones with defined eyes surrounded by intense winds.
Those factors have prompted some early hurricane season forecasts to call for below-normal storm activity.
An average Atlantic hurricane season has about 14 named storms, half of which strengthen into hurricanes, according to data from 1991 through 2020. About three hurricanes a year become “major” storms, with maximum sustained winds of at least 111 mph.
Klotzbach’s team at Colorado State’s Tropical Meteorology Project in April cited a budding El Niño in predicting that this season’s tallies would come short of those averages, with 13 named storms, 6 hurricanes and two major hurricanes. But the forecast also noted the outlook contained “more uncertainty than normal.” The team will offer an updated forecast June 1.
Some forecasters are eyeing chances for increased tropical activity given the unusually warm Atlantic waters.
The Weather Company, which owns weather.com and Weather Underground, and weather data company Atmospheric G2 predicted a near-normal season, with average hurricane activity and 15 named storms. They said in a hurricane season forecast released last month that the ocean temperature trend “gives one pause when relying on the potential El Niño event to keep the season quiet.”
Risks of a damaging season persist
That hesitation is especially true given caution from scientists over whether El Niño predictions will pan out. It is notoriously difficult to predict its development and trajectory when evaluating climate conditions during the Northern Hemisphere springtime.
Even if El Niño forms as expected, weather forecasting models suggest wind shear may remain relatively limited even through the heart of hurricane season, Klotzbach said.
And an active and damaging season could still develop if El Niño arrives later than expected, or in a weaker form, he added.
Besides, meteorologists urge coastal residents to remain storm-ready even in quieter-than-average hurricane seasons. They stress that conditions can allow for devastating storms to make landfall despite larger climatic trends. That warning could be especially apt given the atmospheric battles meteorologists predict in the tropics between El Niño-fueled wind shear and a surge of ocean warmth.
“There’s just no way of knowing which of those is going to be more important in any given week,” McNoldy said.
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