21 years later: Looking back at Tropical Storm Allison
Tropical Storm Allison on June 5, 2001, early in its life, strikes the Gulf coast of Texas and Louisiana. Satellite image is from GOES-8, channel 1 visible mixed with the cloud-free blue marble as background. (NOAA/NESDIS)
HOUSTON - 21 years ago today, and in the days that followed Tropical Storm Allison struck southeast Texas bringing an unprecedented nearly 40" of rain to the area and claiming the lives of dozens locally and beyond. A painful reminder that a storm doesn't need to reach hurricane strength to be devastating, in fact Allison was the first tropical storm name to be retired without ever reaching hurricane status.
The tropical wave developed in the Gulf of Mexico on June 4, becoming a tropical storm the following day 80 miles southeast of the Texas coastline. The night of June 5, it made landfall west of Galveston with 50 mph sustained winds.
Rounds of torrential rainfall followed, intense rates of several inches per hour that lasted for hours on end. One of the unique characteristics of this storm was that it delivered not one, but two devastating blows with the second one being most critical. The slow moving, erratic storm’s initial pass was on June 5-7, 2001. As Allison reached Lufkin, it weakened and stalled before looping back southwest and re-intensifying. From June 8-9, 2001, 28" of rain fell in a 12-hour period during its second pass.
In its wake, it left: over 70,000 homes flooded, 95,000 damaged vehicles, tens of thousands homeless, and roughly $5 billion in local damage. Cars stranded on roads lead to nearly 7,000 documented rescues, with many more civilian rescue attempts. Of the 22 lives claimed locally, most occurred either in vehicles or in attempts to escape those vehicles wading through floodwaters. A painful reminder of why it’s so important to heed "Turn around, don’t drown."
Several factors lead to the unique power of Tropical Storm Allison. When evaluating possible rainfall impacts of a land falling tropical cyclone the following play a key role: storm track/movement, time of day, storm size, topography, wind shear, and nearby weather features. Southeast Texas is flat and Allison was small. The weather profile was eerily quiet aside from the storm, with virtually no wind shear or other weather factors. Ultimately, it was the slow movement of the storm and the time of day that played key roles in addition to the abundance of available gulf moisture that the storm tapped into upon second pass.
This long-lasting June storm remained subtropical for a total of 16 days. It moved on to bring Louisiana 20-30" of rainfall, and up to a foot along other areas of the gulf coast all the way up to the northeast in Pennsylvania over the course of those two weeks. Tropical Storm Allison left a wrath of $9 billion in total damage, making it the costliest Tropical Storm in U.S. History.
Since then, Houston has seen several impactful flooding events including the Tax Day Flood, Memorial Day flood and Harvey to which Allison was the precursor. Funding received post Allison helped update drainage systems and dated flood plain maps, to help us more accurately access risks, and plan and prepare for future flooding events.
With Hurricane Season 2022 already underway, and off to an active start it’s a good idea to review your car, renters, and home insurance policies now for coverage. Many policies do not include flood coverage, and require an additional policy or a rider. The only thing worse than losing everything due to a flood or tropical system, is losing everything and realizing that you won’t receive assistance to replace it.
Here’s hoping for a fairly inactive and safe season for all, though as we know and have experienced in the past... Mother Nature tends to have other plans.