El Niño helps keep the Atlantic hurricane-free as the eastern Pacific logs eight

NOAA's satellites let forecasters follow a tropical wave from its birth over the Ethiopian mountains, the Sahara or the African coast across the Atlantic, and sometimes well into the Pacific ^[14]. More than 60 years after satellites began watching hurricanes, researchers are still learning how those waves form and move ^[14]. Many of the waves that matter start over the Ethiopian Highlands, said Stacy Stewart, a retired National Hurricane Center specialist who now teaches meteorology at Embry-Riddle Aeronautical University [c9, c7].

Dozens of waves leave Africa each year and most never become storms, Kelly Núñez Ocasio, an assistant professor of atmospheric sciences at Texas A&M University, told USA TODAY ^[10]. The Ethiopian ones are likelier to become hurricanes, she said, partly because the mountains help build big storm clusters ^[10]. Some keep going west. They cross the extreme northern end of South America into the eastern North Pacific, where they can seed cyclones there and in the central Pacific, Stewart wrote in an email ^[11].

This year the Atlantic side of that route was hostile at both ends. At the source, drought in Ethiopia left too little thunderstorm activity to build the big clusters and the strong waves that survive the trek across the Sahel, according to the report ^[13]. Over the ocean, shearing winds related to El Niño have broken up the waves that do appear ^[4].

Some waves got through to better water. Fausto and Genevieve grew from disturbances that rolled off Africa near Cape Verde, crossed Central America and strengthened into hurricanes over the eastern Pacific, according to NOAA ^[12]. Stewart linked conditions in both basins, at least partially, to the "super El Niño" ^[7].

The thing this doesn't tell you is how much of the Pacific's season came from Africa. The report names two storms with that origin, out of 18 named storms in the central and eastern Pacific [c12, c6]. Stewart's "at least partially" is as strong as the causal case gets in this record for one El Niño driving both basins ^[7].

Measured against their baselines, the counts are lopsided. The eastern Pacific's eight hurricanes already equal the top of the seven-to-eight range for a whole normal season, with about two months left before the Nov. 30 close ^[1]. Add the basins together and the total is 25 named storms by late September, against a combined full-season norm of 28 to 30 ^[2]. That sum is approximate. The Pacific tally includes the central Pacific, while the norm is quoted for the eastern basin alone [c6, c3].