Monsoon Classroom: The Gulf Surge

What drives the Arizona Monsoon? The blog’s “Monsoon Classroom” breaks down the 5 main patterns that help fire up our Summer storm season.

Gulf Surges are a key contributor to thunderstorm development. Hot air over Yuma develops an area with lower pressure, while cooler air at the mouth of the Gulf of California creates an area of higher pressure. The pressure difference between the two can force a nighttime southerly wind, driving subtropical moisture from the Sea of Cortez into the desert southwest.

There are two flavors of Gulf Surges: weak and strong. Strong surges can be triggered in a few ways. The first is a decaying thunderstorm complex over Mexico, known as a Mesoscale Convective System (MCS for short). Outflow winds from an MCS can force winds to ride up the Gulf of California, allowing moisture to stream in to Arizona.

Another strong surge trigger is a tropical system near the southern tip of Baja California. Winds swirl counter-clockwise around these tropical systems, essentially throwing moisture toward the desert southwest.

Need an example of what a Gulf Surge can do? Look no further than September 8th, 2014. Remnant moisture from Hurricane Norbert triggers a strong surge, contributing to the wettest day ever recorded in Phoenix. Sky Harbor Airport officially picked up a whopping 3.29″ rain in less than 18 hours.


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