"Noaa Hurricane Hunters and Doppler Weather Radars Find Hanna Has Become the First Hurricane of the 2020 Atlantic Hurricane Season," the agency tweeted.
Hanna's outer rainbands were coming ashore in Texas on Saturday morning. The National Weather Service said they could contain heavy rainfall, strong winds and tornadoes.
It was producing maximum sustained winds of up to 80 miles per hour as of 11 a.m. local time (15:00 GMT).
The hurricane may strengthen before its centre makes landfall by late afternoon or early this evening, with rapid weakening expected after it moves inland.