Upper-level low

Importance to cyclones within the subtropics and mid-latitudes

East coast lows form near and east of where a cold core low interacts with a sea surface temperature (SST) gradient along the east coast of continents, such as Asia, North America, southern Africa, and Australia within a pre-existing area of high pressure. Those offshore the East Coast of the United States, which normally form in the months between October and April, are termed nor'easters. Not initially associated with weather fronts, they form in tandem with blocking anticyclones at higher latitudes, which leads to a slow poleward movement up the SST gradient. East coast lows can persist for up to a week. Some East coast lows develop rapidly, becoming meteorological bombs. There is a 4.5 year cycle in the formation of East coast lows near Australia, in years in transition between warm (El Niño) and cold (La Niña) ENSO years. These systems can develop strong wind, heavy rains, waves over 10 metres (33 ft) in height, and eye features on weather satellite imagery. Upper-level lows are usually the cause of heavy rainfall and storms in southeastern Australia, particularly during La Niña years.