Update, Sept. 22 and 29
All rainfalls totals from this storm are still preliminary and require review. But, if verified, these observations would mark the two greatest single-storm rainfall totals on record in the U.S., including Hawaii.
Related stories: Harvey is a 1,000-year flood event unprecedented in scale | We still don’t know how to talk about floods
(This story, first updated on Sept. 22, was revised on Sept. 29 to amend the totals for Nederland and Groves, Tex. based on new numbers provided by the National Weather Service.)
Original post from Aug. 29
The rain from Harvey is in a class of its own. The storm has unloaded over 50 inches of rain east of Houston, the greatest amount ever recorded in the Lower 48 states from a single storm. And it’s still raining.
John Nielsen-Gammon, Texas state climatologist, said a rain gauge near Mont Belvieu at Cedar Bayou, about 40 miles east of Houston, had registered 51.9 inches of rain through late Tuesday afternoon. This total exceeds the previous record of 48 inches set during tropical cyclone Amelia in Medina, Texas in 1978.
All rainfalls totals from this storm are still preliminary and require review. But, if verified, this amount breaks not only the Texas state rainfall record but also the record for the remaining Lower 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 three feet of rain over most of the Houston region, affecting more than 5 million people.
“The 3-to-4 day rainfall totals of greater than 40 inches (possible 50 inches in locations surrounding Santa Fe and Dickinson) are simply mind-blowing that has lead to the largest flood in Houston-Galveston history,” the National Weather Service office serving Houston wrote.
From the perspective of the amount of volume unloaded in the United States from a single storm, Harvey has no rival.
Nielsen-Gammon found Harvey’s total rainfall concentrated over a 20,000-square-mile area 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 Center at the University of Wisconsin at Madison determined that many areas of Southeast Texas have received rain that is expected to come around only once every 1,000 years (or having a 0.1 percent 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.
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