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Characteristics
Easterly waves appear as a long, elliptical trough in the atmosphere. The trough is an area of relatively low pressure that is influenced by the tropical air of the equatorial region known as the Intertropical Convergence Zone, or ITCZ. Due to a high-pressure cell situated above the center of the north Atlantic ocean, easterly winds sometimes develop a cyclonic rotation.
Movement
Easterly waves form due to atmospheric disturbances above Africa, sometimes from as far as the eastern coast. Prevailing winds influenced by the African easterly jet stream cause waves to move westward, toward North America. Easterly waves are also influenced by winds blowing northward from the equator, due to the belt of high pressure known as the subtropical ridge. This influences the easterly wave to move northwestward, often reaching the North American coast.
Hurricanes
The majority of Atlantic hurricanes develop due to easterly waves. The wave acquire a clockwise rotation due to overlying circulating winds in the north Atlantic atmosphere. This rotation causes the easterly wave to develop into a cyclone, which develops into hurricanes. These hurricanes and cyclones disperse due to powerful upper-level wind shear.
Other Effects
The formation of a dry air surge known as the Saharan Air Layer, or SAL, occasionally coincides with an easterly wind. Because its air mass is dry and hot, the Saharan Air Layer rises overtop of the easterly wave. This develops a high-pressure system which brings about cooler air and clear skies instead of weather disturbances. Other times, easterly waves bring less severe storms and humid weather into North America from the tropic Atlantic region.