Harvey may have been downgraded to a storm from a Category 4 hurricane, but it will sit over Texas until the middle of the week – and its legacy will be felt for years to come. It’s being described by the National Weather Service (NWS) as an “unprecedented event”, whose “impacts are unknown and beyond anything experienced” – but what does this mean exactly?
First, a little recap. Hurricane Harvey was once mere remnants of a storm, but when it crossed the Gulf of Mexico it regenerated into an increasingly powerful hurricane. By 1930 hours CDT, shortly before landfall, it was upgraded to a Category 4 beast, with peak sustained wind speeds of 251 kph (156 mph).
The winds were never going to be the most threatening part of the hurricane though. By far, the rain, storm surge, and combined flooding was going to be the greatest risk. At the time, the surge was expected to be 3.7 meters (12 feet) high, and forecasts suggested that parts of Texas would receive as much as 71 percent of its annual precipitation coverage in around two days.
Things have turned out much worse than this. Although it’s now been massively downgraded, the storm has stalled and continues to dump rain on Texas.
It looks like a year’s worth of rain is going to fall on Houston during the course of this storm; already, entire suburbs are submerged, and two dams keeping much of the floodwater back are full. Despite efforts to drain these dams, they are expected to overflow and trigger flash flooding along their margins.
The rivers nearby are swelling, and are expected to continue to exacerbate flooding overnight and throughout Monday. Although Houston has not been issued with a mass evacuation order, it’s not far from receiving one. At the same time, thousands of members of the National Guard have evacuated tens of thousands of people, but a few have died trapped by the floods.
“Ongoing catastrophic and life-threatening flooding will continue across southeastern Texas,” the NWS explains in a recent advisory statement. They add that “the flood threat is spreading farther east into Louisiana.”