A huge hybrid storm is taking shape over the Southwest, combining moisture from Hurricane Polo with a sprawling upper-level system and a surge of moisture from the Gulf.
The result will be several days of heavy rain across Texas, with some areas potentially seeing several inches and an elevated risk of flooding.
So how much rain is coming? Forecasts show the heaviest rainfall developing across parts of West and Central Texas before the threat spreads farther east.
How much rain could Texas get?
The remnants of Hurricane Polo will move out of Mexico Tuesday, Sept. 29, and become incorporated into a large upper-level trough moving across the Southwest, according to the Weather Prediction Center.
At the same time, strengthening winds
near the surface will pull additional moisture north from the Gulf into Texas. That combination is creating an unusually deep plume of moisture that will fuel repeated rounds of showers and thunderstorms.
The Weather Prediction Center has warned of a moderate risk of excessive rainfall across parts of the Southwest and southern High Plains Tuesday, Sept. 29, including all of Texas. Forecasters expect the heaviest rainfall to develop near the Texas-New Mexico border before the focus shifts farther east.
AccuWeather forecasts 4 to 8 inches of rain in two broad corridors from Monday through Friday, including one stretching from near the Texas Hill Country through northeastern Texas and southeastern Oklahoma. Higher localized totals are possible.
Why is this called a hybrid storm?
Polo is not simply dumping rain on Texas as it moves north. Instead, its remnants are becoming part of a much larger weather system.
As Polo weakens over Mexico, its tropical moisture and upper-level energy will interact with an upper-level low moving across the Southwest. That system will help pull moisture northward while Gulf moisture feeds into Texas from below, USA TODAY reported.
AccuWeather meteorologists describe the combination as a new “hybrid storm.”
The National Weather Service in Fort Worth describes a similar setup, with Polo's remnant moisture becoming entrained in the flow around the upper low while strong southerly winds transport Gulf moisture into North and Central Texas.
When will Texas see the heaviest rain?
Tuesday will largely be a transition day for much of Texas as moisture increases.
Rain chances will spread west to east beginning Wednesday, Sept. 30, as the upper-level low approaches and the deep moisture plume expands across North and Central Texas, according to the National Weather Service.
For parts of Southeast Texas, Thursday and Friday, Oct. 1-2, are currently expected to be the peak rainfall days. The Houston-area forecast calls for periods of showers and thunderstorms, with locally heavy rain and a risk of flash flooding.
Exactly where the heaviest rain falls remains uncertain because it will depend on the position and movement of the upper-level low, frontal boundaries and individual thunderstorms.
Where is Hurricane Polo now? See Hurricane Polo path tracker
This forecast track shows the most likely path of the center of the storm. It does not illustrate the full width of the storm or its impacts, and the center of the storm is likely to travel outside the cone up to 33% of the time.
Hurricane Polo spaghetti models
Illustrations include an array of forecast tools and models, and not all are created equal. The hurricane center uses only the top four or five highest-performing models to help make its forecasts.
Gabe Hauari is a national trending news reporter at USA TODAY. You can follow him on X @GabeHauari or email him at Gdhauari@usatoday.com.
Brandi D. Addison covers weather across the nation as the Weather Connect reporter for the USA TODAY Network and contributes to Texas Connect coverage across the state. She can be reached at baddison@usatodayco.com. Follow her on Facebook here.
This article originally appeared on USA TODAY: Hurricane Polo is sending rain to Texas. See how much as hybrid storm hits
