What unusual event occurs during el niño?

When an El Niño kicks in. During an El Niño, the trade winds weaken in the central and western Pacific. Surface water temperatures off South America warm up, because there is less upwelling of the cold water from below to cool the surface.

The pressure gradient decreases. The trade winds weaken, or even blow backwards.

Explanation:

The El nino is the warm phase of the ENSO, that charactics by the southern ocean warm  water that develops in the central and the eastern equatorial zones, and it's accompanied by the high pressure of the western pacific and low pressure of the eastern pacific region. Development of the rainfall in the sept and the nov months, with a high pressure on the east and low on the west. Occurs toward to the cast of the peru and the equador. It thus impacts the climate change and the global warming patterns and the development of the tropical as during the El nino event the subtropical ridge tends to lie near 130 degrees That favours the japan archipelago.