By the evening of August 20, Bret was designated a hurricane following reports of 75 mph (120 km/h) winds during a Hurricane Hunter mission. At around the same time, Bret established a north-northwest track under the influences of a mid-level ridge.[5] The following day, Bret began to undergo rapid intensification,[1] as a well-defined eye developed.[6] On the morning of August 22, the storm attained its peak intensity as a Category 4 hurricane with winds of 145 mph (230 km/h) and a barometric pressure of 944 mbar (hPa; 27.88 inHg).[1] Shortly thereafter, an upper-level trough to the west of the storm began to erode its cloud pattern.[7]