El Nio and La Nia episodes have been shown through numerous studies to have widespread weather impacts, especially on larger scale weather patterns.

But what about their impacts on a more down-scaled basis?

One of the questions we get asked every year is what is the difference between El Nio and La Nia, and how do they impact our Monsoon?

El Nio is a warming of ocean waters in the central and eastern Pacific, which often leads to an increase in rainfall in this area. It also means less surface wind, and in some cases that can lead to a shift from easterly to westerly winds, which can often increase hurricane activity.


So essentially, the warmer the ocean water, the stronger the El Nio, which typically leads to cooler than average temperatures and wetter than average precipitation across the desert.

Now let us compare that to La Nia. La Nia is essentially the opposite of El Nio, meaning cooler than normal ocean waters, leading to stronger winds and usually less hurricane activity for the central and eastern Pacific. And when it comes to temperatures, La Nia typically leads to average desert temperatures, and drier winter months.

But there can also be what we call a neutral pattern, which means neither El Nio nor La Nia. Often, we have averageor close to averagesea surface temperatures, which results in normal hurricane activity and normal winds. A neutral pattern also typically means warmer than average temperatures across the desert, and average annual precipitation.

Want to know more? Check out Monsoon Watch 2024:

Monsoon Watch 2024

The last three transition years where we went from an El Nio Winter to a La Nia Summer were 2007, 2010, and 2016. Rain amounts during those years were either near normal, or well above normal compared to the average rain totals, which is just under 6 at Tucson International Airport.

In general, Monsoon after an El Nio winter typically leans wetter, and wet winters slightly lean to a drier Monsoon.