The remnants of Hurricane Ida unleashed more than a month’s worth of rain on the Northeast in one night, data shows.
An NBC News analysis of National Weather Service rainfall totals found that Ida dumped so much rain — up to 10 inches in some parts of the region — so quickly that several areas saw one-night totals that surpassed their historical averages for the entire month of September.
For example, New York City, which saw flooded subways and where at least nine people died Wednesday, averaged 4 inches of rain in September between 1981 and 2010. Parts of the city received 10 inches during the storm. And Newark, which had a monthly average of 4 inches, received 9 inches of rain.
Flooding from the storm killed at least 42 people, submerged cars and flooded homes, highways and subway systems throughout the region.
Darone Jones, director of the Water Prediction Operations Division at the National Water Center, said the area was primed for flooding, as it had been soaked by tropical storm Fred and Hurricane Henri in the weeks before Ida.
“The rainfall from Fred saturated the ground and elevated the rivers. Then Henri clipped a portion of the same area last week,” Jones said. “The soil moisture was already high, and the streams were already elevated. You add 3 inches per hour rainfall to that, and it starts flooding instantly.”
Jones added that the last time the Northeast saw comparable rainfall was 2011’s Hurricane Irene.
“This was a generational event from a rainfall perspective and flooding perspective,” Jones said. “Those who lived it won’t forget it, and those who lived it probably don’t remember the last time it was this bad.”