Hurricane Irma threatens US' Florida: How it became so huge and destructive

While Irma passed Caribbean islands, those land masses weren't large enough to make it lose momentum

As Hurricane Irma barrels dangerously toward Florida, scientists say that a perfect mix of meteorological conditions has conspired over the past week to make the storm unusually large and powerful.

“You need just the right ingredients for a hurricane of this magnitude to last for so long,” said Phil Klotzbach, an atmospheric scientist at Colorado State University. “And Irma has had them all.”

Weather forecasters had already expected this summer to be an active hurricane season in the Atlantic Ocean because of warmer-than-average ocean surface temperatures, which provide fuel for hurricanes, as well as weaker-than-average wind shear, which can help