Is the weather in El Nino abnormal? Why does it cause extreme weather? Does El Nino often happen?

El Nino is a climate phenomenon, not a weather phenomenon. There is still a difference between climate and weather, and the time and space scale represented by the word climate is much larger. El Nino means that the surface temperature of the tropical Pacific deviates from the historical average by at least 0.5 degrees Celsius. When it is warm, it becomes El Nino, and when it is cold, it is called La Nina. El Nino occurs regularly but irregularly, with a cycle of three to seven years, each lasting six months or even two years. Because the change of shallow seawater temperature also involves the change of sea level pressure, it will lead to the change of airflow and ocean current in the Pacific Ocean and its surrounding areas, and then affect the wind direction and precipitation in the whole region, resulting in a series of extreme weather phenomena. The change of atmospheric circulation accompanied by El Nino phenomenon is called Southern Oscillation. Because these two phenomena are linked, they are generally called El Ni? o Southern Oscillation, which is abbreviated as ENSO in English.