After deep convection developed over the center, it is estimated the system reached tropical depression strength (39 miles per hour (63 km/h)) on September 21, about halfway between Puerto Rico and Bermuda.

[2] On satellite imagery, the depression looked well-organized, with banding features, outflow, and convection, although Hurricane Hunters had difficulty locating a closed center of circulation.

[3] On September 22, the surface circulation rapidly became better organized, and based on confirmation from the Hurricane Hunters, the NHC upgraded the depression to Tropical Storm Humberto.

After passing about 140 miles (230 km) west of Bermuda, Hurricane Humberto turned more to the northeast, and reached Category 2 status on the Saffir–Simpson scale.

Humberto quickly re-intensified and reached peak winds of 105 mph (169 km/h), while located about 200 miles (320 km) south-southeast of Sable Island, off the coast of Nova Scotia.

[6] On September 27, it turned more eastward and later to the east-southeast, and Humberto weakening to tropical storm status about 400 miles (640 km) southeast of Newfoundland.

[1] The cloud pattern became increasingly elongated and removed from the center,[7] and late on the 27th, the circulation of Humberto degenerated into an open trough in the far northern Atlantic Ocean.

[8] Prior to its passage by Bermuda, the National Hurricane Center advised the residents "should monitor the progress of Humberto until it is safely past.