When hurricanes rear up and head for Texas, they can bring anything from drenching rain and street flooding to tornadoes and devastating storm surges. In previous installments of Texas Storm Preparation, we reviewed hurricane categories and what to do if you lived on the Gulf Coast. If you live in the Texas Hill Country, you face different challenges: tornadoes and flash flooding.
To prepare against these, we recommend these helpful storm preparation tips.
1) Understand Tornado Basics
Tornadoes can happen during any storm, but they are even more likely to occur when a hurricane moves into the state. The record for the most tornadoes associated with a hurricane occurred with Hurricane Beulah in September 1967. From Sept. 19–23, this Category 3 storm spun out 115 known tornadoes, all in Texas.
Tornadoes tend to form from low-topped super cells in the eastern half of the outer bands of a hurricane — the highest concentrations of tornadoes occurred about 60–300 miles from the storm’s center. Being away from the main force of hurricane winds, tornadoes can form well inland before the hurricane makes landfall. Short-lived rain-wrapped or night time tornadoes are especially dangerous because they may not appear on Doppler Radar long enough for a warning to be issued.
How dangerous is a tornado?
When a tornado approaches a home, wind will first hurl debris against the structure sometimes in excess of 100 mph. Wind will also cause low-pressure over the roof, causing lift just like an airplane wing. Shingles and roof decking can get torn off. When the funnel passes over the house, pressurized air enters through broken windows and other openings and pushes the exterior walls outward and the ceiling upward as if the home was a being inflated like a balloon. Since roof to wall joints tend to be weakest, the roof flies away first. The walls quickly get pulled away. If the funnel lingers long enough, the interior walls will be swept away as well.
Tornado footage from Briggs/Watson, TX on 06/12/2014
2) Understand Flash Flood Basics
Flash flooding is the number one weather-related killer in Texas, and the Hill Country sees so much of it that’s it’s called “Flash Flood Alley”. The region’s geology of high granite and limestone hills funnels rain down into gulleys and creeks. The thin skin of top soils are unable to hold much moisture so the ground saturates quickly, making flash flooding common.
Rain from Tropical Storm Bill this past June dumped 10 inches in parts, causing surging floods throughout creek and river valleys. Because of this, the Hill Country saw about 2 to 4 inches of rain, with isolated pockets of up to 8 inches. Flash flooding occurred in Austin and San Antonio metro areas, requiring multiple high water rescues.
How dangerous is a flash flood?
Nearly 50 percent of all flash flood fatalities nationwide involve vehicles. Flooded roadways can conceal washed-out bridges or gouged-out roadbeds. A mere 18 inches of water is enough to float a 3,000 pound vehicle and sweep it away with other debris.
Night driving makes it especially difficult to judge water depth and nearly eight of ten vehicle related flood fatalities in Texas occurred between the hours of 6 p.m. and 6 a.m. Remember: Turn Around, Don’t Drown!
Moving water is exceptionaly powerful. One cubic foot contains 7.48 gallons and weighs 62.42 pounds. Flow creates a lot of drag. It only takes about 6 inches (that’s 31.21 pounds) of water to pull an adult off their feet.
Since flash floods occur with large amounts of water suddenly and moving with enormous force, they are capable of destroying structures and moving heavy objects especially if flood waters pass through confined areas such as between tall, steep-sided hills. One inch of rain over one acre of land can produce 27,154 gallons. That’s over 100 tons of moving water. Spread over the 25 counties of the Hill Country, the amount of water rushing towards rivers to the sea is devastating.
3) Stay Informed
1) Listen to the news and weather reports. Hurricane headings and conditions can change hourly. NOAA Weather Radio All Hazards (NWR) broadcasts continuous weather information for Texas directly from the nearest National Weather Service office.
2) Listen for flash flood watches/warnings in your area. If your home is located in a flood plain or low-lying area prone to flooding, consider packing an emergency supply kit and personal items and evacuating to higher ground.
3) Protect your possessions and gather records:
- Copies of insurance policies with your agent’s contact information.
- Document and take photos of all household items and valuables.
- Copies of social security cards, passports, finance records, and receipts of major purchases.
4) Be alert for tornado watches and warnings:
- “Watch” means conditions a favorable for tornados to occur.
- “Warning” means a tornado has been sighted or indicated by weather radar.
5) Make sure your family has or can get to a tornado-safe shelter.
- Take shelter immediately. Find an enclosed, windowless area in the center of the building (closet, hallway, or bathroom) or go underground to a basement or storm cellar .
- If you live in a mobile home — get out! Tie-downs are too weak to withstand tornadoes. You are probably safer outside, even if the only alternative is to seek shelter out in the open. Lie flat on low ground away from your home, protecting your head.
- If your community has a tornado shelter, go there fast.
Don’t have an emergency plan for your family? Make one now! Hurricanes are part of life in Texas and being prepared for one can make all the difference in your family’s safety. Check out TexasPrepares.org for checklists, planning guides, and more so you can be ready when a storm hits.