Over the next few months, the globe might see an uptick in tropical cyclone activity thanks to an El Niño that is showing signs of asserting itself more forcefully.
That doesn’t mean more hurricanes everywhere, though: While El Niño tends to boost activity in the Pacific Ocean, it clamps down on storm formation in the tropical Atlantic. That link has at least one hurricane forecaster calling for a very quiet Atlantic hurricane season this year — possibly the quietest since the mid-20th century...
During an El Niño, a domino of atmospheric effects causes a large area of stable, subsiding air to form over the tropical Atlantic. Exactly the opposite of what a fledgling tropical cyclone, which thrives on instability, needs to grow and strengthen. El Niño also tends to bring more wind shear to the region, meaning the speed and direction of the wind changes more between different altitudes, putting the kibosh on a burgeoning storm....
In an El Niño year, fewer Atlantic storms mean a lower ACE for that basin, while in the eastern and northwest Pacific, longer-lasting storms raise the ACE value. But the changes aren’t equal: The increase in Pacific activity is larger than the decrease in the Atlantic, so “your global activity actually increases in El Niño years,” Klotzbach said.
In particular, activity in the northwest Pacific is a big determinant of global ACE for a given year. There, the tropical cyclone (or typhoon, to use the regional term) season lasts virtually all year, and so there is more opportunity for storms to form.
“The northwestern Pacific drives the bus,” as Klotzbach put it.
http://www.weather.com/science/news/el-nino-strength-what-that-means-for-hurricanes
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