The origins of Hurricane Tanya were from a tropical wave that moved off the western coast of Africa in the middle of October. The wave closely followed the path of Tropical Storm Sebastien and was unable to develop in the tropical Atlantic as it moved westward. The system did not begin to become organized until October 25 while south-southeast of Bermuda. However, the Dvorak technique was still unable to classify the system until October 26 as the low-cloud swirl became better organized while moving northward in the central Atlantic. That evening, a closed circulation had formed, and it was classified as Tropical Depression Twenty-One by the National Hurricane Center. On the morning of October 27, it strengthened into a tropical storm, becoming the 19th as well as the final named storm of the season. Operationally, it was not declared a tropical cyclone until that point, when it was immediately declared Tropical Storm Tanya.