Epic storm: Hurricane Harvey marks the most extreme rain event in US history

By Jason Samenow

The rain from Harvey is in a class of its own. The storm has unloaded at least 1.24m southeast of Houston, the greatest amount ever recorded from a tropical weather system in the lower 48 states. And it's still raining.

The National Hurricane Centre broke the news: "A preliminary report from one Texas rain gauge has broken the Texas tropical cyclone rainfall record. Southeast of Houston, Mary's Creek at Winding Road reported 49.32 inches [1.24m] as of 9am CDT. This total is higher than the previous record of 48 inches [1.21m] set during tropical cyclone Amelia of 1978 at Medina, Texas."

The amount also represents the most from a tropical system in the 48 states.

Hawaii has logged isolated reports of greater amounts at high elevations from tropical systems, but the footprint from Harvey in Southeast Texas is much larger. It has produced at least 1.5m rain over most of the Houston region, affecting more than five million people.

"The 3-to-4 day rainfall totals of greater than 40 inches [101cm] (possible 50 inches [127cm] surrounding Santa Fe and Dickinson) are simply mind-blowing [and] has lead to the largest flood in Houston-Galveston history," the National Weather Service wrote.

Trucks are submerged on Pine Cliff Drive as Addicks Reservoir nears capacity due to near constant rain from Tropical Storm Harvey in Houston. Photo / AP

From the perspective of the amount of volume unloaded in the US from a single storm, Harvey has no rival.

John Neilsen-Gammon, the Texas state climatologist, found Harvey's total rainfall concentrated over 51,799sq km over 72 hours represents nearly 19 times the daily discharge of the Mississippi River, by far the most of any tropical system ever recorded.

The Space Science and Engineering Centre at the University of Wisconsin-Madison determined that many areas of Southeast Texas have received rain that is expected to come around only once every 1000 years (or having a 0.1 per cent probability of occurrence), assuming a stationary climate.

4 day rain total with nearly entire metro area exceeding the 1% annual chance rainfall event (100 yr) and some areas near the 0.1% (1000 yr) pic.twitter.com/12D9sHxNZD

— UW-Madison SSEC (@UWSSEC) August 28, 2017

This is truly an epic storm.