Onslaught of Tropical Downpours to Raise Flooding Risk in Texas, Oklahoma

By Alex Sosnowski, AccuWeather.com Senior Meteorologist

October 20,2015; 10:20PM,EDT

 

 

A dramatic swing from abnormally dry conditions and drought to saturated ground and possible flooding is about to take place in parts of Texas, Oklahoma, Louisiana and Arkansas.
There is the potential for a situation similar to this past May in Texas and in early October in South Carolina to occur. A foot of rain could fall on some communities over the span of three days or less.
As tropical moisture from multiple sources converge on the South Central states, the result will be both beneficial rain and the potential for flooding later this week into early next week.

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The Gulf of Mexico and the eastern Pacific Ocean will take turns at pumping tropical downpours northward into the region.
Rainfall will ramp up and expand eastward over the South Central states during the middle of the week.

The risk of flooding could be far-reaching and affect the major cities of Dallas, Houston, Austin, San Antonio, Amarillo and Brownsville, Texas, to Oklahoma City and Tulsa, Oklahoma, initially.
People in the South Central states should monitor the weather situation for flooding through this weekend and into early next week, regardless of how dry the landscape may be right now.
Rainfall through Friday will generally be beneficial across the region where abnormally dry to drought conditions have re-emerged since the summer. The rain will replenish dry ranges and thirsty lawns.

Flash flooding through Friday will tend to be highly localized.
The early stages of the rain will prime the landscape and increase the stakes for more general flooding beginning this weekend and continuing into early next week.
The first areas to flood will be normally dry stream beds and low water crossings.
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During the weekend and early next week, both the Gulf of Mexico and the Pacific Ocean may send downpours in at the same time.
Areas made saturated by the late-week downpours in Texas and Oklahoma will face the greatest risk of more general flash and urban flooding, as well as flooding along larger rivers this weekend into early next week.
In some communities, the rainfall and flooding could become severe enough to force evacuations.

Additional downpours from an eastern Pacific tropical system, likely to be named Patricia, will stream northeastward across Mexico and into parts of Texas and Oklahoma from Saturday into Monday. The downpours will expand into parts of Louisiana and Arkansas during this time.
Later this weekend into early next week is the most likely time for a tropical system to develop near the Texas coast.
According to AccuWeather Hurricane Expert Dan Kottlowski, "Wind shear will continue to be a deterrent for tropical development in the Gulf of Mexico as it has been over much of the Atlantic basin this year."
Wind shear is a rapid change in direction and speed of air flow at different levels of the atmosphere. Wind shear can prevent a tropical system from forming and cause an organized tropical system to weaken.
If the wind shear was to weaken, there could be enough time for a tropical system to develop slowly in the Gulf of Mexico.
Regardless of whether tropical development occurs, the risk for significant flooding centered on southern and eastern Texas will remain, Kottlowski said.
At the very least, travel disruptions are likely due to poor visibility and heavy rainfall. Lengthy airline delays are possible. Some roads may close. Motorists will need to reduce their speed to lower the risk of hydroplaning.
Never attempt to drive through a flooded roadway. Doing so not only puts you and your occupants at risk for drowning, but also your would-be rescuers. The current could be strong enough to sweep your vehicle downstream into deeper water as 1-2 feet of water is enough to cause most vehicles to lose control.
Parents are urged to keep their kids away from stream banks and culverts. The bank of a stream can give way without notice. Rapidly rising water can sweep onlookers away with little notice.