An easterly wave is a trough of low atmospheric pressure that is located in the tropical areas of the earth on ocean areas. Easterly waves move from the east towards the west. The wind in an easterly wave is cyclonic, however, no closed circulation exists in an easterly wave.

If a closed circulation should develop, the term easterly wave is no longer fitting, and the term tropical depression is employed. The further strengthening of a tropical depression may lead to the development of a hurricane.

Easterly waves develop when warm air drifts off of the continent of Africa onto the Atlantic ocean. Over oceans, atmospheric pressure is higher outside of the tropics. Due to its clockwise circulation, the large transoceanic high-pressure cell or anticyclone centered near the Azores islands impels easterly waves away from the coastal areas of Africa towards North America.

See also

• Anticyclone