Today kicks off this year’s six-month hurricane season in both the Atlantic and central Pacific regions, and a highly energizing El Niño that is rapidly taking shape will at least in part drive how many named storms and hurricanes there will be in each oceanic basin through November 30th.
El Niño’s projected rise to intense proportions is likely to suppress hurricanes in the Atlantic region as it delivers high winds aloft across the Caribbean Sea and out into the tropical Atlantic, according to the National Oceanic and Atmospheric Administration, which issued its seasonal forecast for below-average activity on May 21. Such winds disrupt developing storms that need ambient winds near the ocean’s surface to be generally in concert in speed and direction with winds aloft, to reduce wind shear and allow the fledgling systems to grow.
Strong El Niño winds oppose the typical relatively light surface winds, creating destructive shear that topples and weakens tropical cyclones—which include tropical depressions as well as tropical storms and hurricanes—just as they’re in their formative stages. The enhanced shear from El Niño is projected to lead to fewer named storms and also hurricanes during the season, particularly as it’s expected to worsen in the Atlantic region as the season reaches its most active months of August, September, and October.
The opposite is true in the central and even eastern Pacific hurricane regions during El Niño patterns because the low-level winds align with the upper-level winds, resulting in little to no wind shear to impact growing storms. This season, such conditions favor an abundance of tropical storms and hurricanes in both regions where they could impact Hawaii and Mexico’s Pacific coast much more than usual.
El Niño is the primary reason that NOAA and other seasonal hurricane forecasters’ predictions for this year are average or below for the Atlantic, but above for the central and eastern Pacific, as the image above shows. NOAA is favoring a dip in the numbers of hurricanes with winds of 74 mph or higher and major hurricanes with winds of at least 110 mph in the Atlantic basin compared to average. But check out the outlooks’ number of named storms for Hawaii this year—compared to average it could see an increase of 2-3 times what a typical season has.
El Niño isn’t the only reason the Atlantic season could be quieter. In what’s termed the “main development region” for long-track hurricanes in the tropical Atlantic Ocean that form from disturbances coming off Africa and tend to be the most destructive, sea surface temperatures (SSTs) are running about average or a bit below—far cooler than the past several years in this area between the islands of the eastern Caribbean and the African coast. These cooler SSTs are also expected to temper the numbers of these long-lived storms and hurricanes, according to Colorado State University (CSU).
A long-time leader in seasonal hurricane forecasting, CSU this year is calling for 13 named storms, 6 hurricanes, and 2 major hurricanes—slightly below average—compared to a normal season with 14 storms and 7 hurricanes, 3 of which attain major Category 3-4-5 intensity. Warmer-than-average SSTs elsewhere in the Atlantic, particularly off the East Coast and in the Gulf of Mexico, could make up the difference, supporting tropical cyclone formation.
That is far from the case in the eastern and central Pacific regions, where SSTs are well-above average and will only warm even more as El Niñ’o’s warm waters move in and expand. Hawaii’s central Pacific Ocean becomes its warmest and breeds the most named storms and hurricanes during El Niño years.
Odds are high that this year’s event attains the designation as a ‘Super” El Niño, with SSTs warming to at least 2°C above average in the tropics. The last Super El NIño in 2015 fired up Hurricane Patricia in the eastern Pacific—a 215 mph monster that became the Western Hemisphere’s strongest on record.
The wildcard during hurricane season always involves landfall, which impacts people the most and most severely. And that’s where National Weather Service Director Ken Graham steps in to reiterate that “it only takes one storm to make for a very bad season.” Think 1992, when the Atlantic Ocean birthed just six named storms, but kicked off the season with catastrophic Hurricane Andrew slicing through South Florida and then central Louisiana. Graham stresses that people living along and even inland from the Atlantic and Gulf coasts focus on making their plans now for any eventual threat this year, despite the lower-than-usual forecast for the Gulf and East Coast waters.
“Although El Niño’s impact in the Atlantic basin can often suppress hurricane development, there is still uncertainty in how each season will unfold,” Graham said at a news conference when the seasonal forecasts were released. “That is why it’s essential to review your hurricane preparedness plan now,” he added.
While some hurricane forecasts aim beyond the seasonal numbers and project the odds of landfalling storms each year, largely the science is not there to do this more accurately. In fact, most seasonal forecasts, such as NOAA’s, note that the day-to-day and week-to-week weather patterns that steer tropical storms and hurricanes throughout the season set up on a scale of days to a week or maybe two, making specific projections unavailable across a months-long season.
| ATLANTIC | HURRICANE | SEASON | NAMES |
| Arthur | Gonzalo | Leah | Rene |
| Bertha | Hanna | Marco | Sally |
| Cristobal | Isaias (ees-ah-EE-ahs) | Nana | Teddy |
| Dolly | Josephine | Omar | Vicky |
| Edouard | Kyle | Paulette | Wilfred |
| Fay |
NOAA’s seasonal forecast will be updated in early August, just ahead of the season’s historical peak months. CSU will update its April 9 hurricane season forecast on June 10, and then again in early July and August.
