A man works to clear a drain in flood waters, Friday, Sept. 29, 2023, in the Brooklyn borough of New ... [+]
Historic flooding is happening in the New York City Metropolitan area, and it is still raining. According to the Associated Press, the seemingly biblical rains closed portions of the iconic subway system and strained critical transportation arteries throughout the city. At the time of writing late Friday afternoon, multiple accounts of stranded motorists and water rescuues were being reported. The city is currently under a State of Emergency and the National Weather Service in New York urged people not to travel Friday evening in affected areas. Here are four stunning facts to know about the ongoing and dangerous flooding in New York City region.
The Wettest Calendar Day On Record At John F. Kennedy Airport
It was certainly expected that Friday would surpass the previous record at John F. Kennnedy airport for wettest September day, previously 5.83 inches from Hurricane Donna (196). However, today’s non-hurricane event went even further. The National Weather Service posted on the platform X that September 29th, 2023 is now the wettest calendar day on record at John F. Kennedy Airport. As of Friday afternoon, 7.88 inches of rainfall had fallen, which eclipses the previous record of 7.80 inches. And it is still raining. Records at JFK date back to 1948.
A line of heavy raintorms draped over parts of New York and Connecticut on September 29th, 2023.
Rainfall Continues Into Friday Evening For Parts Of The Area
New York City emergency managers warned that rainfall is expected into Friday evening, and weather experts agree. Kieran Bhatia is a weather expert at Guy Carpenter posted model forecasts through Saturday afternoon. Heavy rainfall is still a possibility for portions of Long Island and Connecticut. He emphasized that much of the heavy rainfall over New York City had subsided for now. However, the National Weather Service Friday afternoon discussion warns, “There continues to be potential for scattered to numerous instances of flash flooding, especially in urban and poor drainage areas. Locally considerable and life threatening flash flooding remains possible where axis of heaviest rain develops and sits for several hours.”
The Meteorological Scenario That Caused Epic Flooding In The New York City Region
As a meteorologist, I decided to dig into the National Weather Service forecast discussion issued overnight Thursday into Friday morning. Some clear signs of a significant flood event were evident:
- Strong moisture fetch from the Atlantic Ocean was expected to flow into the area through Friday evening.
- In inverted trough of low pressure was present at the surface.
- A very saturated atmosphere with high end precipitable water values over 1.5 inches - Precipitable water is used to quantify the amount of water vapor in. column from the surface to upper reaches of the troposphere.
- A frontal focusing mechanism, convergence and upper level low pressure.
The forecast discussion went on to say, “ The CAMs are producing some extreme results, with rainfall totals exceeding 10 inches in some models in some areas. While this may be overdone, the signal is there for some high end rainfall totals, particularly when considering the NAM has been suggesting max totals in the 5-6 inch range.” Interestingly, one of my class lectures today discussed the importance of moisture and that a warming atmosphere has more water vapor capacity. Studies continue to suggest that rainfall rates are intensifying as a response. It is likely that climatologists will conduct future climate attribution studies on this event to understand potential meteorological - climate connections.
Until that happens, it was clear to me that the meteorological setup was omnious. The moisture fetch, expected surface boundaries, and lifting mechanisms created an ideal environment for a “training/backbuilding” event in which heavy rainfall would fall or develop in the same location for a sustained period of time. In some cases, rainfall rates of two inches or greater per hour were likely happening. Such circumstances produce a very dangerous equation: Extreme Flooding = high rainfall intensitys + quasi-stationary + moist atmosphere + urbanized surfaces.
Surface map valid Friday evening September 29th, 2023.
Government Shutdown Threatens Flood Insurance Program
Ironically, political turmoil in Washington D.C. has brought the country to the brink of another federal government shutdown. Thankfully, our courageous National Weather Service colleagues will still be working to keep us safe. However, it is disgusting that they continue to be pawns and may have to endure financial uncertainty until backpay is awarded. Why am I mentioning the shutdown? According to numerous sources, the shutdown could force the National Flood Insurance Program to stop issuing new policies. The FEMA website notes, “The NFIP provides flood insurance to property owners, renters and businesses, and having this coverage helps them recover faster when floodwaters recede.” Go figure.
