January 25 2018 read full Washington Post article here
Hurricane Harvey unleashed a tropical deluge probably unsurpassed in U.S. history, the National Hurricane Center says. In an in-depth meteorological review of the storm released Thursday, the center said it was unable to identify any past storm that had unloaded so much rain over such a large area
Different color shades show the likelihood of the amount of rain in different areas of Southeast Texas in a given year. For example, the dark blue shaded area indicates less than a 1 in 1,000 chance of happening in a given year in that location. (NOAA Office of Water Prediction)

“[I]t is unlikely the United States has ever seen such a sizable area of excessive tropical cyclone rainfall totals as it did from Harvey,” the report said. By one estimate, the storm dispensed more than 33 trillion gallons of water over Texas and the southern United States.

….The report confirmed that peak rainfall totals reached record-crushing levels, just over 5 feet near Nederland and Groves, Tex., near Port Arthur. “Both of these values (and from five other stations) exceed the previously accepted United States tropical cyclone storm total rainfall record of 52.00 inches at Kanalohuluhulu Ranger Station, Hawaii, in August of 1950 from Hurricane Hiki,” the report said.

Isolated rainfall amounts might have even been more extreme. The report noted that radar estimated totals “as high as 65-70 inches in southeastern Texas.”

The excessive rainfall was caused in large part when the monster storm stalled over the Lonestar state, drawing moisture from the warm Gulf of Mexico and dumping punishing torrents over an extended duration. Additional factors helped intensify and focus some of the extreme rainfall. “While Harvey was very slow moving over Texas, not all drifting cyclones produce such torrential rain totals,” the report explained. It said Harvey interacted with a weak cold front over the region, which “hardly moved” and intensified the rainfall.

The consequence of such excessive rainfall was one of the most expensive natural disasters in U.S. history. “Harvey is the second-most costly hurricane in U.S. history, after accounting for inflation, behind only Katrina (2005),” the report said.

The report does not discuss the possibility that Harvey’s rains were affected by human-induced climate change, but independent analyses published in peer-reviewed journals found the heating of the air and sea from climate warming may haveboosted Harvey’s rainfall output by at least 15 percent….

Eric S. Blake and David A. Zelinsky. Hurricane Harvey, 17 August – 1 September 2017, National Hurricane Center/NOAA Report, January 23 2018