The city of Houston was at a standstill as I-45 north of downtown became a river after tropical storm Allison dumped 28 inches of rain in 24 hours. The storm prompted Texas Gov. Rick Perry to declare a state of emergency in Harris and 28 other southeast Texas counties. (Richard Carson/Reuters)

Texas is frantically preparing for what in all likelihood will be the most devastating storm in over a decade. Forecasters are saying soon-to-be Hurricane Harvey will be a slow-motion disaster — reaching the coast as a major hurricane on Friday and lingering over the same location through the weekend.

Residents of Southeast Texas — not just those along the coast — should be preparing and stocking up on food, water and other essentials. This hurricane’s biggest threat looks likely to be extreme rainfall and flooding, which will occur well away from the coast.

According to the National Weather Service, 59 percent of all tropical cyclone-related deaths in the United States since 1970 have been caused by freshwater flooding, whereas only 12 percent can be attributed to wind. If nothing else, this illustrates the urgency with which residents must heed all forecasts and evacuation orders.

We can look back on previous storms for an idea of what eastern Texas may be forced to endure in the coming days, but there’s one that stands out in Texas weather history: Tropical Storm Allison.

Allison was never a hurricane, it was “just” a tropical storm with a lot of water trapped inside. As it neared the Texas/Louisiana coastline on June 5-6, 2001, nearly 10 inches of rain fell in five hours across southwest Louisiana, alerting forecasters to potential trouble when the system struck Houston.

Clear skies and moisture streaming inland from the Gulf set the stage for significant flash flooding on June 8-9, and widespread thunderstorms dropped over a foot of rain by sunrise on June 10.

Unfortunately, the majority of Allison’s rain fell over the populous Houston metro area. According to the National Weather Service’s post-storm Service Assessment, “two-thirds of Harris County (Houston) received over 10 inches of rain.” Isolated spots in northeastern Houston racked up more than 20 inches of rain.

More than 45,000 homes and 70,000 vehicles fell victim to the floods, while inundations in the Texas Medical Center led to the loss of decades’ worth of medical research.

Meanwhile, the 22 deaths that resulted from the deluge offer some insight as to what not to do during a flood situation. Nearly half of all the deaths occurred in automobiles. If you cannot see the road beneath floodwaters, then turn around. Just a few inches of rapidly-moving water can sweep your vehicle off the road, and oftentimes the water may be deeper than one would think.

Several deaths were also caused by electrocution. For the same reason we wouldn’t use a toaster while taking a bath, avoid entering floodwaters at all costs. Oftentimes, utility poles and live wires may be submerged — acting as giant toasters in a neighborhood-sized bathtub.

Allison’s winds never exceeded 70 miles per hour, but the $10 billion in damage and biblical flooding prove that a storm doesn’t have to be a hurricane to be a catastrophe.