The Big Apple is closing in on a top-10 rainfall year, and AccuWeather meteorologists explain what’s been behind all of the rain in and around New York this year.
New York City and other portions of the Northeast have encountered several prolific rainfall events this year. Heavy rainfall of historic proportions and disastrous flooding from multiple events this summer and early fall have led to the loss of dozens of lives and billions of dollars in damage. The city's rainfall tally thus far this year ranks third-highest.
Since early this summer, a big reason locations like New York City have been above average in terms of rainfall can be linked to an ocean phenomenon known as a marine heat wave, according to AccuWeather Senior Long-Range Meteorologist Paul Pastelok.
At its most basic definition, a marine heat wave is a prolonged period during which sea-surface temperatures are unusually high, according to the National Oceanic and Atmospheric Administration (NOAA).
Higher water temperatures allow more moisture to evaporate from the ocean into the atmosphere. When storms are able to tap into an abundance of moist air in the atmosphere, more rain is able to fall harder and faster.
A daily sea-surface temperature anomaly (degrees above/below normal) map for Nov. 1, 2021, shows the marine heat wave continuing well into autumn as depicted by the red areas off the mid-Atlantic coast of the U.S. (NOAA)
AccuWeather forecasters say a marine heat wave over a portion of the Atlantic Ocean, just off the United States coast between Delaware and eastern New England, led to an overabundance of moist air across portions of the mid-Atlantic and Northeast during the second half of the year and is likely a key factor in the severity and frequency of heavy rain events.
This current surge of warm water can be traced back to July 2020. It became warmer and progressively widespread during this past summer, according to AccuWeather Lead-Long Range Forecaster Paul Pastelok.
"This warm body of water has lasted through big storms this season and has not been ruffled," Pastelok said. He noted that had there been multiple storms moving south to north from the tropics during the past several months, then perhaps this area may have cooled.
3-day Total rainfall is shown from four recent events affecting New York City: Early July, Hurricane Henri, Hurricane Ida, and the late-October nor'easters. Yellow indicates rainfall of over 4 inches. (NOAA).
"It may take several big nor’easters to really knock down these water temperatures," he said. Although AccuWeather's long-range team is forecasting the potential for a few big storms this year, which may lower sea-surface temperatures late this winter, there can be more warm surges at any time going forward, he added.
Up until June 1, the beginning of meteorological summer, New York City was actually lagging slightly behind normal in terms of rainfall. Then, disastrous storms began to arrive. By November, parts of the I-95 corridor had rainfall as much as 16 inches above normal.
In early July, heavy thunderstorms triggered widespread flooding concerns across the New York City metropolitan area. Just a day later, Elsa, as a tropical storm, would go on to reinvigorate flooding issues for the region.
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In late August, Henri, which made landfall in New England as a tropical storm, brought torrential rainfall to New York City and broke several precipitation records, including the wettest hour ever recorded in Central Park. During the hour between 10 p.m. and 11 p.m. on Aug. 21, 1.94 inches of rain deluged Central Park, where official weather readings are taken in New York City. As the National Weather Service (NWS) put it, that interval was the "wettest hour on record" for the city, with records dating back to the late 1860s.
That new record would not stand for very long.
Ida, a storm that will live in infamy for many across the Southern and Eastern states, struck Louisiana as a Category 4 hurricane on Aug. 29, and then crossed the eastern half of the country and arrived in the northeastern U.S. as a tropical rainstorm as the calendar flipped to September.
Danny Hong and his wife Wenqing Ou are emotional as they talk to reporters in front of their flooded home in the Flushing neighborhood of the Queens borough of New York, Thursday, Sept. 2, 2021, in New York. The remnants of Hurricane Ida dumped historic rain over New York City, with at least nine deaths linked to flooding in the region as basement apartments suddenly filled with water and freeways and boulevards turned into rivers, submerging cars.(AP Photo/Mary Altaffer)
Ida would go on to unleash a widespread 6-8 inches of rain across the New York City metro area. As a result, Sept. 1 marked Central Park's fifth-wettest day on record, according to the National Weather Service (NWS).
Less than two weeks after setting a new record for the wettest hour ever recorded, Central Park recorded a staggering 3.15 inches of rain in the hour between 8:51 p.m. and 9:51 p.m. from Ida, shattering the record yet again. Ida's rainfall also prompted the NWS to issue the first-ever flash flood emergency for New York City.
The damage unleashed in the Big Apple and surrounding areas from Ida's flooding rainfall was catastrophic. Floodwaters quickly overwhelmed roadways and subways, leaving many people stranded. Water also gushed into low-lying areas and basements, inundating everything in its path.
More than 50 deaths were attributed to Ida's impact on the Northeast, according to ABC News.
"When Ida tracked northeast from the Gulf Coast, the storm's rain bands intensified when the storm moved closer to the mid-Atlantic," Pastelok said. "The storm provided the lift of the very warm, moist based situation over these warm spots leading to 2-3 inch rain rates and around 9 inches of rain."
Changes in the ocean currents and ocean salinity over the past 10-20 years, likely influenced by climate change, may also be contributing to these coastal marine heat waves.
"Oceans are a heat sink for the earth system," AccuWeather Chief Meteorologist Jonathan Porter said. "In other words," he added, "it is a place that the earth system stores excess heat from the atmosphere. Given that the atmosphere has warmed substantially in recent decades due to climate change, it is not surprising to see sea-surface temperatures running above their long-term averages in many parts of the world."
And that is a trend that continued this year. Temperatures across the contiguous U.S. during the summer of 2021 were the hottest ever recorded in American history, according to NOAA, and July 2021 earned the dubious distinction as the "world's hottest month ever."
A 2018 study published in the science journal Nature detailed how maritime heat waves have become more frequent over the past century.
"From 1925 to 2016, global average marine heat wave frequency and duration increased by 34% and 17%, respectively, resulting in a 54% increase in annual marine heat wave days globally," the researchers said.
In addition to rainfall attributed to these notable events, frequent storminess at a smaller scale this summer and fall has pushed New York City into the record books.
As of Oct. 31, New York City's Central Park recording station stood at 57.21 inches of rainfall for the year - the third highest year-to-date total in recorded history.
Even if it didn't rain another drop in the city for the rest of the year, 2021 would end up being the 15th wettest year on record. Just another 1.22 inches of rainfall in the remaining two months of the year will catapult 2021 into the top 10 wettest years on record.
The wettest year on record occurred in New York City in 1983 when an astounding 80.56 inches of rain fell. Nearly 2 feet of rain stands between 2021's running total and the title of wettest year on record in New York City.
Records at the Central Park observing station date back more than 150 years to 1869.
While there is quite a distance between 2021's running total and the title of wettest year on record, AccuWeather forecasters say Mother Nature is expected to present plenty of opportunities to make up ground.
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