(Puerto Rico) — Hurricane Irma has strengthened into an “extremely dangerous” Category 5 storm, threatening to slam into northeastern Caribbean islands and Puerto Rico by Wednesday before possibly taking aim at the US mainland.

Irma was churning Tuesday morning in the Atlantic about 270 miles east of Antigua and Barbuda, heading west with maximum sustained winds of 175 mph — well above the 157 mph threshold for a Category 5 storm.

The storm’s forecast track currently has it near or over Antigua and Barbuda by late Tuesday or early Wednesday, and the Virgin Islands and Puerto Rico on Wednesday afternoon.

Computer models show the system eventually heading toward Cuba and possibly turning north toward Florida by the weekend.

While Irma’s exact path is uncertain, several islands in the Caribbean as well as Florida are bracing for the storm.