Monsoon 101: Madden-Julian Oscillation - Tucson News Now

Monsoon 101: Madden-Julian Oscillation

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A wave of tropical energy called the Madden-Julian Oscillation (MJO) can affect monsoon action here in Arizona. 

The MJO originates in the Indian Ocean and then travels east, across the Pacific Ocean. This wave enhances tropical storm formation as it reaches the west coast of Central America and South America. Increased tropical activity in this area of the ocean can then make its way up the west coast of Mexico, eventually pushing monsoon moisture into Arizona. The MJO cycle ranges from 30 to 60 days, meaning a new wave arrives every one to two months. 

The below loop shows storm action across the globe from the last three days. It is made up of data from four different satellites. The yellows and reds indicate where convection (rain and storms) are covering the planet. Look for a mass of brighter colors moving eastward along the equator between the Indian Ocean and the west coast of Central America. During the summer months, this may indicate a MJO.


Below is one of the MJO forecasts for the next 40 days. Orange indicates favorable MJO conditions. As the orange approaches the west coast of Mexico and Central America, tropical storm activity is expected to increase. This can result in an uptick of monsoon storm action in Arizona days to a week later. Click here to see other computer model forecasts.

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