NYC flooding: What caused the sudden, severe deluge in the Northeast?
NEW YORK - All was quiet in New York City Wednesday evening as the remnants of Hurricane Ida moved toward the Northeast. But things quickly changed.
To the surprise of many, Wednesday evening’s storms in the region brought historic rain, deadly flooding and severe tornadoes.
In fact, Wednesday’s torrential rainfall was so severe that it prompted the National Weather Service to issue a flash flood emergency in New York City — the agency’s first such warning for the city ever.
The storm dumped massive amounts of rain in just a few hours causing widespread flooding across New York and New Jersey.
The NWS's flash flood emergencies issued are reserved for "exceedingly rare situations when a severe threat to human life and catastrophic damage from a flash flood is happening or will happen soon."
RELATED: How much rain did we get from Storm Ida?
Prospect Park in Brooklyn topped the list in New York City for rainfall totals with 8.8 inches of rain. Central Park got a total of 8.2 inches. The iconic Manhattan park also broke a record for the amount of rain that fell in one hour. 3.15 inches of rain fell between 8:51 p.m. and 9:51 p.m. That is, by far, the wettest hour ever recorded in New York City.
"We’re enduring an historic weather event tonight with record-breaking rain across the city, brutal flooding and dangerous conditions on our roads," New York Mayor Bill de Blasio said while declaring a state of emergency in New York City late Wednesday.
In fact, many locations in New York City received as much as 1.5 inches of rain in just 15 minutes at the peak of the storm.
"When rainfall rates get that high in a highly urbanized area such as the I-95 corridor in the Northeast, with a lot of paved ground surface, severe flash flooding would be expected and water can build up quickly. And with Ida, we did see the highest rainfall rates occur right in the I-95 corridor from Philadelphia up to New York City," Alex Lamers, warning coordination meteorologist at NOAA, said.
At least two dozen deaths occurred in New York City, New Jersey and Pennsylvania as the relentless rain caused flooding throughout the region. Video captured by New York City residents showed floodwaters pouring into the city’s underground subway system.
Some 150,000 customers lost power in New York, New Jersey, and Pennsylvania, and at least 24 people died in the flash flooding, trapped in their homes or cars. Parts of Central New Jersey clocked 11 inches of rain in less than 24 hours, and a tornado destroyed a neighborhood in South Jersey. Other parts of the region were badly hit as well.
One storm cell spawned at least three tornadoes Thursday, with at least two touching down in Maryland.
But why did the sudden flooding and severe weather happen, and could record-rain events be the new normal in the region?
Why did it flood in the Northeast?
It may come as no surprise that one of the primary reasons for the severe flooding that impacted the Tristate area Wednesday was from the remnants of Hurricane Ida
Prior to Ida’s impact on the Gulf Coast, the hurricane was able to strengthen and intensity due to very warm ocean water in the Gulf of Mexico and low wind shear in the atmosphere.
This ideal setup caused Ida to make landfall as a major Category 4 hurricane Sunday afternoon — coincidentally on the 16-year anniversary of Hurricane Katrina — with record-tying sustained winds of 150 mph in Louisiana.
And as with any powerful hurricane or tropical storm, once it made landfall, the friction caused by the storm’s contact with land caused it to weaken.
By Monday evening, Ida had already been downgraded to a tropical depression as it moved across Mississippi with maximum sustained winds of 35 mph.
The storm system was always projected to move northeast, but since Ida was no longer an organized weather system when it got closer, it left many surprised that it could manage to deliver the kind of flooding the region hasn’t seen in a decade.
RELATED: DEADLY FLOODING: Bodies pulled, others rescued in NYC, NJ storm waters
But as the storm’s remnants moved northward, there was already a stalled-out front — a non-moving boundary between two air masses — impacting the region. The lift from this front enhanced Ida’s rain, making it heavier than it typically would be.
"As Ida began to interact with a stalled front over the Mid-Atlantic on Wednesday, it produced multiple tornadoes and very heavy rainfall within about 150 miles of its track in the Mid-Atlantic and Northeast," Lamers said. "Tropical cyclones that approach or affect the continental United States will often interact with a front at some point in their lifecycle. In the middle latitudes on the planet, which is where the U.S. is located, fronts are far more common and stronger than in the tropics."
On Monday, meteorologists noticed this likelihood, and the Weather Prediction Center issued a high-risk outlook for excessive rainfall in the region.
"When you look at the significant impacts from Ida in the Northeast, the extreme rainfall and resulting flash flooding definitely stands out," Lamers continued. "Although hurricanes are an obvious coastal hazard, they are capable of producing dangerous weather conditions well inland from the landfall point, even after the maximum sustained winds have decreased. Two of the most common inland hazards with tropical cyclones are flooding and tornadoes," Lamers said.
Could climate change also be to blame for the flooding?
Ida hit the Tristate area less than two weeks after Hurricane Henri broke rainfall records in the Northeast.
Were the record-breaking rains coincidental, or can the area expect more severe flooding in the future?
"We do occasionally see hurricanes affect similar areas in the same year. It is more common in active hurricane seasons, and there were several examples last year. Louisiana was affected by multiple tropical cyclones, and Hurricanes Laura and Delta had landfall points within about 10 miles of each other a little more than a month apart," Lamers explained.
"Repeat tropical cyclone impacts would be less common in the Northeast, since tropical cyclones are less common there overall. However, there was an example just last year as Fay and Isaias moved into the Northeast less than a month apart, and Isaias produced some significant flash flooding," Lamers said.
And while it will take time for climatologists and researchers to understand how the climate affected Hurricane Ida specifically, many scientists believe climate change and the warming of Earth’s atmosphere have caused more precipitation in recent years.
The Clausius-Clapeyron equation shows that for every 1 degree C temperature increase, Earth’s atmosphere can hold 7% more water. And since the air becomes more saturated with water for every degree the planet warms, rain is heavier when it does come down.
This means future storms like Ida could turn out worse.
One study, published in Advancing Earth and Space Science in 2019, suggests that as the planet continues to warm, extreme rainfall events will continue to become an increasingly common part of life for many heavily populated parts of the world.
In another study, researchers at the University of Bristol analyzed future projections of hurricane rainfall in the Caribbean and found that climate change could result in extreme hurricane events being as high as five times more likely.
RELATED: Climate change may make extreme hurricane rainfall 5 times more likely in the Caribbean, study suggests
"The findings are alarming and illustrate the urgent need to tackle global warming to reduce the likelihood of extreme rainfall events and their catastrophic consequences, particularly for poorer countries which take many years to recover," said lead author Emily Vosper, research student at the School of Computer Science at the University of Bristol.
According to the Fourth National Climate Assessment, the most torrential downpours in the Northeast now unleash 55% more rain compared to the 1950s and could increase another 40% by the end of the century.
"Global warming is upon us," Senate Majority Leader Chuck Schumer said at a press conference Thursday. "When you get all the changes we have seen in weather, that’s not a coincidence."
And if sudden severe weather events do become more frequent, it could bring a wake-up call to officials on infrastructure in the Northeast.
On Thursday, the governors of New Jersey and New York emphasized the need for climate resiliency. "As it relates to our infrastructure, our resiliency, our whole mindset, the playbook that we use, we’ve got to leap forward and get out ahead of this," New Jersey Gov. Phil Murphy said.
The Associated Press and FOX 5 New York contributed to this story.