Hurricane Harvey will be remembered as one of the most destructive hurricanes to ever strike the United States. The storm erupted from a weak tropical wave into a category 4 hurricane in just three days, coming ashore near Corpus Christi, Texas, late in the evening on August 25. Such a powerful storm hitting land is normally a catastrophe in its own right, but the tragedy that followed this storm wasn't caused by the wind or the ocean—it was the rain, and lots of it. Texas endured one of the worst flooding events in American history after Harvey lingered over the state for nearly a week and dropped more than three feet of rain on Houston, the country's fourth-largest city.
The hurricane's intense winds and storm surge devastated some of Texas's coastal communities near Corpus Christi, including the small towns of Rockport and Port Aransas. Wind gusts peaked above 100 mph across most areas in the path of the storm's eye. Weather instruments measured winds as high as 132 mph near Port Aransas as the eye came ashore on August 25. Hundreds of homes and businesses were damaged or destroyed by the storm's intense winds.
Under normal circumstances, a hurricane would make landfall and move out of the area within 24 hours. Late-night hurricanes typically end with residents surveying the damage by the first light of day. Harvey was not one of those storms. The storm stalled out over Texas after making landfall, meandering over the same area before reemerging over the Gulf of Mexico to make a second landfall in Louisiana five days later.
The bulk of Harvey's unprecedented rains fell on the Houston metropolitan area, a region that's notorious for flooding due to its geography and heavily urbanized landscape. Water has few places to go when heavy rain falls on such impermeable land. The influx of water quickly overwhelms narrow waterways and outdated drainage systems, leading to frequent stream and street flooding. The factor that separates this storm from previous flooding disasters in southeastern Texas is that this rain was worse than anything in recorded history, more than doubling the rainfall totals seen during the infamous floods unleashed by Tropical Storm Allison in 2001.
Houston's George Bush Intercontinental Airport recorded 32.17 inches of rain between August 25 and August 29, while Houston's Hobby Airport—where the runways were flooded out for a time during the height of the storm—saw 38.22 inches of rain over the same period. The two airports both average about 50 inches of rain in a normal year. Various rain gauges around the area measured totals even higher than the two airports. A rain gauge in Cedar Bayou, Texas, just north of Galveston Bay, saw more than 52 inches of rain in five days.
Emergency officials and volunteers performed thousands of water rescues for people stranded in their homes and vehicles as the waters rose. The exact number of fatalities won't be known until crews can search every vehicle and home once the waters recede. The Washington Post quoted local officials as saying that floodwaters covered more than 30 percent of Harris County, home to Houston, during the height of the ordeal.
The perfect mix of ingredients came together to make Hurricane Harvey a historic disaster. Tropical cyclones require warm water, low wind shear, and ample moisture to develop and thrive. Once the tropical wave that seeded Hurricane Harvey's development hit the Gulf of Mexico, it had all three of those ingredients in abundance. The storm rapidly intensified under these perfect conditions, strengthening right up until it came ashore. But what made the storm especially destructive is that it didn't move after landfall.
Tropical storms and hurricanes are steered by winds through the atmosphere. Weaker storms are driven by prevailing winds close to the surface while strong storms like Harvey are steered by winds throughout the entire depth of the atmosphere. Harvey's path took it right into an area where there were no steering currents to force the storm to keep moving inland and away from Texas. The calm pattern around Harvey kept it locked in place, forcing the storm to meander for days after landfall, slowly tracking in a loop before making its way back out over the water.
Preliminary measurements show that Hurricane Harvey was the wettest tropical cyclone in American history, producing several reports of rainfall that break the previous all-time record. Cedar Bayou, Texas, will hold the unfortunate distinction of most rain ever recorded during a tropical cyclone, having measured 51.88 inches of rain by the afternoon of August 29. Even if that reading doesn't hold up to scrutiny, there were several more that beat the previous record of 48.00 inches set in Tropical Storm Amelia back in August 1978. Just over 49 inches of rain fell on a gauge near Pearland, Texas, a city that lies about halfway between Houston and Galveston.
Houston wasn't the only area devastated by the heavy rain. Houston gets the most coverage because it's home to the most people, but the scenes that played out there also unfolded in countless small towns and communities across the region. Extreme rainfall totals greater than three feet extended east of the metro area into southwestern Louisiana. The Texas cities of Beaumont and Port Arthur, which lie near the state line with Louisiana, saw more rain than Houston proper. The airport in Port Arthur measured nearly four feet of rain during the storm.
The rainfall isn't the only record set by Harvey. The storm put an end to the unprecedented streak of days without a major hurricane making landfall in the United States. The last hurricane rated category 3 or stronger to strike the country was Hurricane Wilma back in October 2005. Harvey was also the strongest hurricane to hit Texas since the 1960s.
Harvey wasn't the absolute worst case scenario for a hurricane hitting the Houston area, but it was a close second. Harvey will be remembered for its rainfall the same way Hurricanes Katrina and Sandy are remembered for their storm surge. This storm would have been magnitudes worse if it had made landfall in Houston proper rather than 150 miles down the coast. Category 4 winds and storm surge funneling into Galveston Bay would have made this an unimaginable tragedy, but nearly four feet of rain in five days comes pretty close.