After becoming a tropical storm, Gert quickly intensified due to the presence of an anticyclone aloft, as well as warm water temperatures exceeding 84 °F (29 °C). Following the development of a warm spot near the center, Gert intensified into a hurricane on September 13. It strengthened further, developing an eye that briefly dissipated before reforming. Early on September 15, Gert attained major hurricane strength, or a Category 3 on the Saffir-Simpson scale. Still moving west-northwestward, Gert continued its steady intensification trend, developing well-defined outflow throughout the circulation that was described as "outstanding". After reaching Category 4 status on September 15, Gert strengthened further to peak winds of early on September 16, as estimated on satellite imagery through the Dvorak technique. Satellite intensity estimates reached as high as , or a Category 5 hurricane. At the time, the hurricane was located about 720 mi (1160 km) east-northeast of Guadeloupe in the Lesser Antilles. Around the time of peak intensity, Gert maintained a round central dense overcast. Hurricane Hunters investigated the hurricane on September 16 and indicated a slight weakening trend due to an eyewall replacement cycle. Gradually Gert turned toward the northwest due to a weakness in the subtropical ridge, created by Hurricane Floyd to the west. As it did so, the hurricane re-intensified briefly before resuming a weakening trend, due to increased wind shear and an upper-level trough to its west restricting outflow.