El Niño tends to suppress the formation of hurricanes and tropical storms in the Atlantic. Indeed, in anticipation of an El Niño this summer, many institutions that produce seasonal hurricane forecasts are looking for a season – June 1 to Nov. 30 – less active than usual.
The reason: Changes El Niño brings to atmospheric circulation patterns increase the average intensity of wind shear over the Caribbean and tropical Atlantic, where the storms form. Wind shear refers to a change in wind speed or direction with height. This shear blows warmth and moisture away from the storm’s center, where they are needed for the storm to intensify and grow.
Shear also can disrupt the storm's vertical structure. While an El Niño year can mean fewer hurricanes, forecasters have been quick to caution that Hurricane Andrew slammed into south Florida in August 1992 as a category 5 storm – the most powerful rating. It was an El Niño year.
