A tropical disturbance is a meteorological event in tropical or subtropical waters that maintains its area of organized convection for at least 24 hours. These disturbances, which have a nonfrontal migratory character, are typically 100 to 300 nautical miles in diameter.
When the climatic conditions are conducive, a disturbance can gain strength and develop into a stronger storm having a closed circulation, such as a tropical depression, tropical storm or hurricane.
In some cases, a tropical disturbance measurably alters the wind field. When this is accompanied by the disturbance's travel from east to west through the tropics, it is also referred to as an easterly wave.