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Monsoon 2014 Forecast

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Monsoon 2014 kicks off on June 15.  That means all the monsoon numbers for the year start to go in the record books.  However, monsoon storms generally hold off the good downpours until the beginning of July in Arizona. 

This year the factors that influence whether it will be a good or bad monsoon are conflicting. First the good factors. 

Good 1. Drought in the Plains states. 

Drought in the north Texas, Oklahoma, and Kansas can help set up the high pressure system that takes over the eastern U.S. during the summer. The dry conditions mean this area will heat up quickly this summer.  This draws the summer high, which is normally centered over Bermuda, to the west. The circulation around this high helps to keep the southerly flow of tropical moisture into Arizona through the monsoon. 

Good 2. Active tropical season forecast off the west coast of Mexico. 

Warmer than average sea surface temperatures associated with El Niño are appearing off the west coast of Mexico and Central America. This warm water provides the fuel needed for tropical storms and hurricanes.  If this moisture surges north, monsoon rain totals could add up to some impressive numbers very quickly. However, tropical moisture surges also raise the threat of flooding in the area. 




Good 3. Not much drought in northern Mexico.

The monsoon downpours start in Mexico in June and then migrate northward, generally arriving in southern Arizona in early July. As the mountains in Mexico soak up monsoon rain and turn a healthy green, some of this moisture is then returned to the atmosphere by the plants through a process known as evapotranspiration. This process adds to the monsoon moisture heading northward into Arizona. If the mountain foliage is healthy, then the monsoon can move out of Mexico into Arizona that much quicker. However, if there is drought in northern Mexico, this can slow the progression of the monsoon into Arizona.  

This year, although conditions are dry in northern Mexico, there isn't much drought. As monsoon storms pour down over the Mexican mountain ranges, the dry conditions will hopefully be erased quickly and push the monsoon into Arizona sooner rather than later. 


The good factors listed above may be offset somewhat by bad factors that can break up the monsoon atmospheric set-up needed for the downpours. This year, many of these factors may have a bad influence early in the summer but generally have less influence as the monsoon progresses.

Bad 1. El Niño years trend towards drier.

While the developing El Niño indicates an increase in tropical activity in the East Pacific, the warmer ocean temperatures also weaken the land-sea temperature contrast. This in turn can weaken the southerly flow needed for that tropical moisture to reach Arizona. 

In Tucson, 10 of the last 17 El Niño summers have been drier than average. The Tucson National Weather Service crunched the numbers and you can click here for an interactive map that shows El Niño-Monsoon rain totals for your area. Below is the listing for Tucson.




Bad 2. Spring snow in the southern Rockies. 

Although Arizona and New Mexico had a dry winter with limited rain and snow totals, the Rocky Mountains in Colorado still have quite a bit of snow. This snowpack can delay the movement of an area of High pressure out of Mexico, through Arizona, and into the Four Corners area. The movement of this high provides the June heat. But once it gets to the Four Corners this High opens the door for tropical moisture to surge north. As long as the High is in Mexico or over Arizona, the chances of storms remain limited. 

As the summer progresses and this snow melts away and the influence weakens. This can therefore delay the monsoon, but not necessarily keep it from being a good year overall. 

Then there is the Madden-Julian Oscillation (MJO), which has short-term positive and negative influence on the monsoon from week to week. The MJO is a wave of tropical energy moving west to east across the Pacific Ocean. As this energy approaches the west coast of Central and South America it can ramp up tropical activity, which can then ramp up monsoon action in Arizona a few days to a week later. 

In the below graphic, when the orange color reaches the East Pacific Ocean this is good for the monsoon. 
To sum it all up, when an El Niño or developing  El Niño coincides with the monsoon, summers tend to be drier in Arizona. However, a forecast for increased tropical activity off the west coast of Mexico could still mean the area will get some good downpours, especially late in the summer and early fall when hurricane season peaks. 

Copyright 2014 Tucson News Now All rights reserved.





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