 A tropical wave emerged into the Atlantic from the west coast of Africa on August 28 . While tracking west @-@ northwestward , satellite imagery indicated a developing low @-@ level circulation . After significant deep convection formed , the system was classified as Tropical Depression Eight at 1200 UTC on September 1 . Because of potentially unfavorable wind shear , only slight intensification was forecast . The depression tracked west @-@ northwestward under the influence of a subtropical ridge to its north . Because of satellite intensity estimates of sustained winds of 40 mph ( 65 km / h ) , increased deep convection , and improvements in outflow , the depression became Tropical Storm Ernesto at 0600 UTC on September 2 . 
