after becoming a tropical storm, it had an eye, a clear opening at the center of the storm. 6 hours later since becoming a tropical storm, the national hurricane center (nhc) named it tropical storm maria. on september 17, maria turned to move west-northwest and quickly becomes a category 1 hurricane. in just 12 hours, it became a category 5 hurricane with maximum winds of 160 mph (260 km/h) on september 18.