Hurricane Isaias is a typical storm — but it’s also ‘astounding’

Hurricane Isaias is expected to hit somewhere between the Mississippi coast and the Florida Panhandle late Friday as a Category 2 storm, with winds strong enough to cause widespread damage and a storm surge of up to 7 feet. What makes it notable isn't the storm itself but its timing: this is the first hurricane of the Atlantic season, which started back in June. That breaks the previous record for the latest first hurricane by about a month.

The delay comes down to El Niño, a warm-water pattern in the Pacific that affects weather worldwide. It has been creating dry air and wind shear (winds blowing at different speeds and directions at different altitudes) over the Atlantic, conditions that choke off hurricane formation even though the ocean surface has been warm enough to fuel storms. Isaias found one of the few gaps in that pattern, forming in the Gulf of Mexico where conditions were less hostile. Oddly, while the Gulf's surface water is running hot, the deeper water is unusually cool, which matters because hurricanes churn up water from below as they move. That could limit how much Isaias strengthens.

For anyone along the Gulf Coast, the practical concern is the storm itself: dangerous winds and significant flooding risk from storm surge, regardless of how unusual its timing is. Meanwhile, the eastern Pacific has seen an unusually active season, and Hurricane Rachel is currently expected to bring rough surf and wind to Baja Mexico and Southern California this weekend.