After some strengthening on July 6, Bertha was upgraded to a hurricane early on July 7 as satellite and microwave imagery indicated an eye feature had formed. It continued to strengthen that morning. Fast strengthening continued that afternoon and Bertha strengthened into a major hurricane with 125 mph (195 km/h) winds and a well-defined eye. The strengthening trend stopped early on July 8, due to wind shear, and Bertha quickly weakened back to a Category 1 hurricane that afternoon.