 A tropical wave exited the west coast of Africa on September 7 and spawned a low pressure area by the following day . At 18 : 00 UTC on September 8 , a tropical depression developed about 225 mi ( 360 km ) west @-@ southwest of Dakar , Senegal . The depression moved steadily westward and intensified into Tropical Storm Humberto early on September 9 . Despite moderate wind shear , Humberto continued to strengthen while passing south of Cape Verde , due to a moist atmosphere and warm ocean temperatures . The storm brought squalls to Cape Verde . The southwestern islands experienced wind gusts exceeding 35 mph ( 55 km / h ) which downed several trees . Heavy rains in many areas triggered flooding that washed out roads and damaged homes . Offshore , the freighter Rotterdam went missing with a crew of six amid 10 to 16 ft ( 3 to 5 m ) swells . The vessel eventually reached São Tomé and Príncipe , though that country 's port institute and coast guard denied her entrance . Later on September 10 , the storm 's deepening briefly halted as it curved northwest in response to a developing mid @-@ level trough over the central Atlantic . 
