Easterly waves are disturbances in the area close to the ITCZ which take the form of a line of thunderstorms orientated N/S moving from East to West. The West African Tornado is an example of an Easterly Wave but they do occur in other areas and they are the origin of tropical revolving storms.
The ITCZ is a line of low surface pressure following the so-called ‘heat Equator The isobars run parallel to the ITCZ with pressure values increasing away from the ITCZ Occasionally a ripple will appear in the isobars which is just like a trough of low pressure at higher latitudes. This disturbance moves from East to West and is known as an Easterly Wave in contrast to the Polar Front Westerly Waves. Easterly Waves form close to the ITCZ between latitudes 5 deg and 20 deg N/S.
The weather associated with Easterly Waves is quite severe A line of cumulonimbus and thunderstorms aligned North/South will form along the trailing Easterly edge of an Easterly Wave. This line of active CB aligned North/South and moving from East to West is known as a tropical tornado. Approximately one in ten Easterly waves will develop into a tropical revolving storm. The West African Tornado is the source of hurricanes in the Caribbean.