When we think about tropical weather, our minds immediately go to the Gulf of Mexico. And that’s not wrong — at least from June to September. However, when late September and October roll around, instead of watching what comes off the coast of Africa, we should be watching what develops along the west coast of Mexico. Why?
- In October, it’s what develops in the Pacific Ocean, not the Atlantic, that most often brings rain to San Antonio
- Pacific Hurricane Madeline played a large role in the Flood of ‘98
- Several other Pacific tropical systems have brought flooding to South-Central Texas
- October is when fall fronts can combine with a still ongoing Pacific tropical season to bring healthy rainfall
In the summer, the pattern can often be stagnant and the jet stream lives up in Canada. By fall, as the northern hemisphere begins to tilt away from the sun, cold air starts to spill south. As a result, storm systems take shape and move west to east across the United States. As fall wears on, these storm systems dip farther and farther south. They begin to sweep cold fronts through Texas. These storm systems and fronts act as barriers to Atlantic tropical storms and hurricanes. Even if a tropical system makes it into the Caribbean, it’s often quickly pulled north before it can make it to Texas. In other words, it’s hard for Atlantic tropical weather to make it to San Antonio once we start seeing fronts.
But, that doesn’t mean we can’t see tropical rainfall. The source just changes. In October, the eastern Pacific is still cranking out tropical storms and hurricanes. Meantime, those storm systems sweeping across the United States can draw the tropical activity north. All that thick, tropical moisture gets drawn into the United States and can pool it along a cold front. Should that happen, heavy rain is a good bet. History tells us so. One of the best representations is the Flood of ‘98.
On October 17, 1998, a strong upper-level storm, a front, low-level gulf moisture, and tropical moisture from Hurricane Madeline combined to produce one of the worst floods San Antonio has ever seen. And it’s not the only example.
- Last year, on October 24, heavy rain arrived in South Texas courtesy of Hurricane Roslyn. The storm actually held together as it crossed over Mexico and arrived in Texas.
- San Antonio saw high water rescues on October 13, 2021, when thick moisture from Hurricane Pamela streamed into South Texas and resulted in flooding rainfall.
- On October 24, 2015, more than 4″ of rain fell in San Antonio, as many places across Texas saw flooding rains. The source of moisture was Pacific Hurricane Patricia.
- Hurricane Norma in mid-October of 1981 brought a deluge to Texas, as the system and all of its moisture streamed north across the state.
These are just some examples, as there are likely many more. Bottom line: when the calendar flips to October, look to the Pacific to help us break this drought.