September 19, 2019

Texas Reels From Another Historic Flood After Imelda Drops Nearly Four Feet Of Rain

The remnants of Tropical Storm Imelda triggered yet another flash flood emergency in southeastern Texas, the fourth time this region has had to deal with historic, devastating floods in the last four years. Since Tuesday, the Beaumont area has seen bands of intense thunderstorms redevelop and sit over the same areas for hours at a time, producing nearly four feet of rain in some areas. The rain will slowly wane over the next day, but the damage is done.

A tropical wave moving across the northern Gulf of Mexico quickly strengthened into Tropical Storm Imelda on Tuesday as it made landfall. The disturbance organized into a tropical depression, strengthened into a tropical storm, and made landfall near Freeport, Texas, all within a two-hour window on Tuesday afternoon.

Imelda came ashore beneath a large ridge of high pressure over the eastern two-thirds of the United States; the storm's weak structure and the lack of steering currents meant that there was nothing to keep the storm moving north and away from the Houston/Beaumont areas. As a result, the system and its remnants have meandered over southeastern Texas for three full days. Ample tropical moisture and several sources of forcing allowed bands of thunderstorms—which produced 500,000 lightning strikes (!!!) in ten hours on Wednesday—to train over the same areas for hours at a time.

Some observing stations around Beaumont have seen more than three-and-a-half feet of rain since this all began on Tuesday. A foot of rain in one afternoon can trigger significant flash flooding just about anywhere; once you climb up two, three, four feet of rain, there's just no way to handle that even if you have the best infrastructure possible. The ground can't handle it. Natural waterways can't handle it. Man-made sewer systems can't handle it. Since it has nowhere else to go, the water just builds up and floods neighborhoods that have never experienced significant flooding before. This is why we hear "we've never flooded around here" after each of these events. Areas you don't think can flood really can flood if it rains hard enough for long enough.

Despite the system's rapid development, residents had plenty of warning that heavy rain would lead to flash flooding across southeastern Texas regardless of whether or not the disturbance became a named storm. Flash flood watches went into effect while the system was still over the Gulf. Local meteorologists went out of their way to make sure everybody knew the risks. However, there were few indications beforehand that rainfall totals would rival some of those seen in Hurricane Harvey just two years ago.

According to the National Weather Service office in Houston, the highest preliminary rainfall total from this event was 43.15" near Beaumont in Jefferson County, Texas. If that total verifies, the office said, it would make Tropical Storm Imelda the seventh-wettest tropical cyclone on record in the United States, and the fourth-wettest on record in Texas. This would also beat out Tropical Storm Allison's highest rainfall total of 40.68 inches; that storm in June 2001 served as the benchmark for tropical cyclone flooding for all subsequent storms until Harvey.

Tropical Storm Imelda is the fourth historic flood event in southern Texas in the last four years, following Memorial Day 2015, Tax Day 2016, and Hurricane Harvey in 2017. The Carolinas suffered tremendously in the flooding left behind by Hurricanes Matthew (2016) and Florence (2018). It's easily forgotten that Hurricane Barry, which made landfall (and produced two feet of rain) in Louisiana this past July, broke the all-time tropical cyclone rainfall record for the state of Arkansas after producing 16.17 inches of rain in the town of Dierks.

It's a common comment among meteorologists and weather enthusiasts during this event that there are few weather maps with a color scale large enough to cover the spread of rainfall totals. Topping-out the color scale on a rainfall map is a fairly arbitrary marker, but it demonstrates how unusual it is to see so many extreme rainfall events in such a relatively short period of time. We could go years without ever seeing another tropical system produce more than three feet of rain, or we could have another next month.

It's hard to link any one weather event directly to climate change, but it's also hard not to look at all these heavy rain events and ignore the influence climate change may play in current flood disasters and future storms. A warmer atmosphere is able to hold more moisture, which creates more opportunities for thunderstorms to produce heavier downpours. A changing climate will accentuate the extremes—dry spells will grow drier and flooding rains will grow even heavier.

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I graduated from the University of South Alabama in 2014 with a degree in political science and a minor in meteorology. I contribute to The Weather Network as a digital writer, and I've written for Forbes, the Washington Post's Capital Weather Gang, Popular Science, Mental Floss, and Gawker's The Vane. My latest book, The Skies Above, is now available. My first book, The Extreme Weather Survival Manual, arrived in October 2015.