2 Months of Rain in a Day and a Half: New York City Sets Records

Did you hear it rained a lot the other day?

Well, it did. Let’s start with the record books. The rainiest hour on record in New York City (1.94 inches from 10 to 11 p.m. on Saturday) produced the rainiest Aug. 21 on record (4.45 inches), which was followed immediately by the rainiest Aug. 22 on record (2.67 inches).

This deluge, courtesy of Tropical Storm Henri, has in turn produced what is already the fifth-wettest August on record, coming on the heels of the third-wettest July on record to make this the second-rainiest summer ever recorded in the city — 23.36 inches so far, as of Monday afternoon.

That is very nearly two feet of rain.

In 36 hours from Saturday night to Monday morning alone, 8.05 inches of rain fell in Central Park.

That is almost two months’ worth of rain in a day and a half.

If it had been snow, there would have been nearly nine feet of it.

We asked a meteorologist at the National Weather Service in Upton, N.Y., to characterize this weather event.

“It’s a large amount of water to fall from the sky in such a short period of time,” said the meteorologist, Dominic Ramunni.

Think about it.

“It really is,” he added.

Maybe eight inches doesn’t seem like that much.

But it’s actually quite a lot. An inch of rain falling on an acre of land weighs about 113 tons. Eight inches of rain on the 302.6 square miles of New York City weighs about 175 million tons and comprises more than 42 billion gallons of water.

This is where you run into problems. The city’s ancient combined storm-sewer system was not built to handle that.

What it was built to handle is only 3.8 billion gallons a day. Everything beyond that, runoff and sewage mixed together, spews into the harbor. Either that, or it backs up into the street, though Vincent Sapienza, the city’s environmental commissioner, said on Monday that happens a lot less than it used to — and that the street flooding that popped up around the city this weekend could have been much worse, considering how much rain fell.

The city is building a parallel system of pipes that will handle just storm water, but it has thousands of miles of pipe to go. “It’s going to be decades,” Mr. Sapienza said.

Videos taken in the underground subway system show the rain pouring down as freely as if indoors were outdoors, though Aaron Donovan, a spokesman for the Metropolitan Transportation Authority, said that despite there being “tens of thousands of openings where water can get into the subway system,” there were only a few brief, localized service disruptions.

Copious amounts of rain were recorded throughout the region. According to amateur weather observers cited by the Weather Service, 9.22 inches fell on Oakland, N.J., in Bergen County, 9.85 inches were recorded along the East River in Brooklyn Heights, and nearly eight inches fell on Prospect Park in Brooklyn, where a staircase was magically transformed into a waterfall.

Here is another way to think about the rain: In Central Park, the official rainfall is measured using a device called a tipping rain gauge. Every time a measurable amount of rain — one hundredth of an inch — falls into the cup of the gauge, the cup tips the water out, advances a counter and resets. (“I got my parents one for Christmas a few years back,” Mr. Ramunni of the Weather Service said. “Actually it was more of a gift for me.”)

During that one hour Saturday night when nearly two inches fell, the gauge was tipping every 19 seconds.

The whole year has not been like this. Precipitation in the first half of 2021, in fact, was 13 percent below normal..

But since July 1, half of the days have had measurable rainfall in New York City. Every other day — drip, drip, pour.

What’s scary, of course, is that large amounts of rain may become less and less rare.

“I don’t want to wade too deeply into this,” Mr. Ramunni said, “but with a warming climate you’re going to see more water vapor in the air, and more water vapor in the air leads to more rain.”

What is all this rain good for, then? Mushrooms, you might think. And July was an amazing month for them. “You couldn’t take a step anywhere without stepping on a mushroom,” said Paul Sadowski, secretary of the New York Mycological Society.­

But even mushrooms have their limits. A mushroom is what is known as the fruiting body of a mostly underground life form. After July’s explosion, the rains of August found the city’s fungi exhausted.

“The whole fungal organism — its whole point in existing is to reproduce,” Mr. Sadowski said. “Once it’s produced its fruiting body, it’s done.”