 A tropical wave exited the coast of Africa on September 16 . It traversed steadily westward , with the southern portion of the wave axis moving across northern South America . On September 26 the wave entered the eastern Pacific Ocean near Panama , and slowly organized . A weak low @-@ level trough extended from the Caribbean Sea to south of Mexico , disrupting the normal flow of westward steering currents . On October 3 , the tropical wave developed a distinct area of deep convection , and began to drift eastward to the south of Mexico . Two days later a low @-@ level circulation formed , and midday on October 5 the system developed into Tropical Depression Eighteen @-@ E while located about 250 miles ( 410 km ) south @-@ southwest of Huatulco in the state of Oaxaca . 
