"How did Isaias manage to form and strengthen despite El Niño?" — Sarah

You’ve likely heard that El Niño makes it more difficult for storms like Isaias to form. 

The reason that El Niño is often associated with less active hurricane seasons is because it provides stronger winds than usual above 10,000 feet. This creates a shearing effect for storms that makes it harder for them to form, and when they do form, it makes it harder for them to grow. 

El Niño’s wind shear is often largely contained to the Caribbean, or farther south than where Isaias formed. 

There have been seasons in the past that have managed to produce strong storms despite a strong El Niño.

The image below shows several hurricanes that have formed during super El Niño seasons from 1972 to 2015.

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In reality, even in the Caribbean, all storms need is a pocket of more favorable conditions. This has happened several times this season, most recently with Tropical Storm Gonzalo, which formed near the Cabo Verde Islands off the coast of Africa, another typical dead zone in El Niño. 

Isaias formed in one of these pockets in the Bay of Campeche.

And even though it felt more shear near landfall, the winds aloft were more aligned with the direction Isaias moved, instead of slamming into it directly from the west.

Those upper-level winds also spread apart above the hurricane, another factor that allowed it to strengthen or maintain its intensity, rather than quickly weakening.

That wind shear was associated with the typical autumn jet stream making a visit to the Gulf Coast and is not strongly tied to El Niño in this case.

Jonathan Belles has been a digital meteorologist for weather.com for 10 years. His favorite weather is tropical weather, but also enjoys covering high-impact weather and news stories and winter storms. He's a two-time graduate of Florida State University and a proud graduate of St. Petersburg College.