After becoming a tropical storm, Edouard quickly strengthened due to the establishment of an upper-level anticyclone over the storm. The storm moved to the west in response to a strong subtropical ridge to its north, and Edouard strengthened into a hurricane on August 23. Due to very favorable conditions, the hurricane rapidly strengthened on August 24 and August 25 to peak as a 145 mph (230 km/h) Category 4 hurricane on the Saffir-Simpson Scale. A weakness in the subtropical ridge allowed for a motion more to the west-northwest, and the hurricane passed about 250 mi (400 km) north of the Lesser Antilles on August 28. For three days during this time, Edouard maintained Category 4 intensity, though weakened late on August 28 due to an eyewall replacement cycle and vertical shear.