Hot take: This time of year, Pacific tropical activity is more important to San Antonio than what forms in the Atlantic

When fall rolls around, we should turn our attention to the west coast of Mexico

The Pacific Ocean becomes the place to watch for tropical moisture as we get into October. (Copyright 2023 by KSAT - All rights reserved.)

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?

Key Points:

  • 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.

Footage from KSAT shows the Oct. 17, 1998, flood in San Antonio and South Texas. The Alamo City officially got 11.26″ of rain that day. (KSAT)

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.
This satellite image taken at 15:30 UTC and provided by NOAA shows Hurricane Roslyn approaching the Pacific coast of Mexico, Saturday, Oct. 22, 2022. Roslyn grew to Category 4 force on Saturday as it headed for a collision with Mexicos Pacific coast, likely north of the resort of Puerto Vallarta. (NOAA via AP)
  • 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.

About the Author:

Justin Horne is a meteorologist and reporter for KSAT 12 News. When severe weather rolls through, Justin will hop in the KSAT 12 Storm Chaser to safely bring you the latest weather conditions from across South Texas. On top of delivering an accurate forecast, Justin often reports on one of his favorite topics: Texas history.