Hurricane Preparedness Week: Torrential Rain and Inland Flooding

A flooded Houston freeway with just the top of a crane sticking out of the water.

The Southwest Freeway Near Downtown Houston after Tropical Storm Allison

Tropical cyclones produce copious amounts of rain. The energy released when rain drops condense are what provide the storm with it’s high winds. Conversely to wind speed, it is the less intense tropical cyclones that produce the most rain.

It is not uncommon for a major hurricane to dump 12 inches of rain across a wide area, but a weaker storm can easily produce local amounts that exceed two feet or more. Torrential rains cause inland flooding when waterways and flood control systems are overwhelmed by the influx of rain.

Don’t be caught unaware. Visit the National Hurricane Center website for more information.

Extreme Rain

One-quarter of all deaths associated with hurricanes are caused by inland flooding. One characteristic of tropical cyclones is their slow movement, and weaker storms can stall or move even slower than strong storms. This allows more rain to fall in localized areas and the result is catastrophic flooding.

In 2001, Tropical Storm Allison formed out of a tropical wave over the Gulf of Mexico in early June. It struck the Texas coast and moved inland, eventually reaching Luftin, Texas where it met a high pressure system and stalled before it changed direction and moved back over the Gulf of Mexico.

While over Texas, Allison dropped more than 40 inches of rain. Houston had 70,000 flooded homes and more than 30,000 people were left homeless. Forty-one people died as result of the storm. Damage estimates in Texas topped 5.5 billion dollars.

But Allison wasn’t finished. It’s remnants stalled again over the Gulf of Mexico. It then moved to the northeast and strengthened. It made landfall a second time at Morgan City, Louisiana with winds of 45 MPH.

Twenty one tornadoes added to the destruction.

Inland Flooding

Tropical Storm Allison is a good example of why coastal and inland residents should not rely on the Saffir-Simpson Scale as a measure of a tropical cyclone’s strength. Allison was a relatively weak tropical storm that formed very early in the season, but it had a long history and a track that took it across a wide swath of the Gulf and Mid Atlantic States.

Photographer Jim Occi captured these photos of gas lines in Cranford on Thursday following Hurricane Sandy.

Photographer Jim Occi captured these photos of gas lines in Cranford on Thursday following Hurricane Sandy.

More than 230 flash flood warnings were issued by the National Weather Service while the storm was over land. Even after Allison crossed the southern states and moved over the Atlantic Ocean, it continued to dump rain over a wide land area all the way to Long Island and Massachusetts, and inland flooding followed the rain, resulting in road closures and evacuations.

The Red Cross opened nearly fifty shelters and served more than 300,000 meals during the disaster. Because of the extreme rainfall and the extent of the inland flooding, Tropical Storm Allison was the deadliest and most costly tropical storm in the history of the United States, even though it was a relatively weak tropical cyclone.

Inland Flooding Preparation

NOAA logo for the all hazards weather radio systemWeather radios are an essential piece of equipment for every household in the United States. Weather alerts issued by the NOAA and the National Weather Service are invaluable information tools, and knowledge can save your live and the lives of your family.

Flash flood warnings saved hundreds of lives in Texas during Tropical Storm Allison. The average advance notice before a flood was just 39 minutes, and a weather radio can give you the most up to date information available ahead of local news stations who must receive the information, interpret it, and then rebroadcast it.

Purchase flood insurance. Most homeowner insurance policies explicitly deny coverage for damage caused by flooding. Flood insurance is government guaranteed insurance program that mitigates damage and loss of property from a flood.

Inland flooding also contaminates water supplies. Each person needs a minimum of one gallon of drinking water per day, and another gallon for personal hygiene. Stock potable water in containers, and store it above rising water levels.

Isolated by flood waters, a backup generator for emergency home use can keep your food cold, your sump pump running, and even run your air conditioner. Standby generators work with an automatic transfer switch to isolate your home from the electrical grid and local distribution system while supplying you with the power you need to keep your family and property safe. They are automatic systems that operate on a home’s natural gas or propane supply and can run for extended periods without the need for refueling.

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