Author: Firas Saleh, Director - Insurance Product Management, Moody's
When a slow-moving cold front shifting east over the Northeast United States interacted with warm, moist air drawn from the Atlantic at the start of last week, the National Weather Service (NWS) had to respond to a fast-evolving, escalating storm scenario.
On Monday, July 14, 2025, the NWS issued nearly 100 flash flood warnings primarily across the mid-Atlantic and Northeast US states, the most warnings ever issued by the NWS in a single July day.
Figure 1: Total number of flash flood warnings issued by the Weather Forecast Office (WFO) on July 14, 2025. (Source: Iowa State Environmental Mesonet)
The NWS warned that showers and thunderstorms could bring rainfall rates up to two inches (50 millimeters) per hour in states from northern Virginia, Pennsylvania, Maryland, New York, New Jersey, through to Massachusetts. For potentially hard-hit areas, the NWS issued advanced flood warnings, and in response, flood alerts were declared, such as in all five New York City boroughs.
As July 14 progressed, more than 50 million people were hit by torrential rain and flash flooding. A multi-state emergency had occurred, with flooding reported in Newark, New Jersey, New York City, northern Virginia, and southern Maryland, according to the NWS.
With a 60% increase in recent decades, the Northeast has experienced the largest regional increase of extreme precipitation in the U.S., according to a government report published in November 2023.
Figure 2: Total number of flash flood warnings issued by the Weather Forecast Office (WFO) from January 1, 2025 to July 14, 2025. (Source: Iowa State Environmental Mesonet)
More than 3,000 flash flood warnings have been issued so far this year by NWS offices around the US, with the current count higher than any previous year through July 14, 2025 since records began in 1986.
Widespread impact across the Northeast US states
Excessive rain across the Northeast saw Mount Joy in southeastern Pennsylvania record more than seven inches (178 millimeters) of rainfall in under five hours. In Brewster, New York, in the Hudson Valley, two inches of rain fell in just 30 minutes, Staten Island saw seen about four to six inches (102 to 152 millimeters) of rain, but it was the city of Plainfield, New Jersey, with six inches of rain in less than two and a half hours, that made the headlines.
Declaring a state of emergency, New Jersey Governor Phil Murphy said that flash flooding had devastated many communities on the night of July 14, especially in Union and Somerset counties. The Governor spoke about two deaths in Plainfield after a car was swept on deep, fast-moving floodwater into a stream and about a home explosion in the borough of North Plainfield.
"We're seeing more of this [rainfall], more frequent and more intense. Six inches of rain in under two and a half hours, in two waves, one wave, knocked a lot of these communities a little bit off kilter; the second one just came in for the kill. So we're assessing around all these communities and counties."
This was in addition to three people who were killed in Plainfield on July 3 from falling trees when severe thunderstorms swept through New Jersey.
New York struggles with aging infrastructure
For New York City (NYC), the event on July 14 was a similar playbook to the flash floods on September 29, 2023, where nearly six inches (152 millimeters) of rainfall occurred at Central Park in the heart of Manhattan, and again in September 2021.
The NWS Central Park weather station recorded 2.07 inches (52 millimeters) of rainfall between 7 p.m. and 8 p.m. local time on July 14, the highest rainfall ever recorded in NYC in one hour in any July and the sixth-highest hourly total since records began in 1869.
The highest hourly rainfall was recorded on September 1, 2021, when 3.15 inches (80 millimeters) fell from the remnants of Hurricane Ida, which caused 14 deaths in New York, most of whom died in flooded basement apartments.
Water gushed into the NYC Metro subway system, suspending the main 1, 2, and 3 lines, flooding stations such as 28th Street, and pouring water into carriages. While the city’s subway systems are designed to drain a maximum of 1.75 inches of rainwater per hour, compared to the 2.07 inches of rain that fell.
New York City’s sewer system reflects the city’s development since the 17th century. Big expansions in the late 19th and early 20th centuries mean the average age of the city’s sewage mains is 84 years.
The current NYC sewer infrastructure comprises an extensive network of over 7,400 miles (11,909 kilometers) of sewer pipes that collect sanitary sewage and stormwater. Approximately 60% is combined, which means it is used to convey both sanitary and storm flows. Combined sewer overflows (CSOs) are another element of concern, occurring when heavy rainfall overwhelms the city’s combined sewer system, causing a mixture of stormwater and untreated sewage to discharge directly into local waterways.
The standard stormwater design criterion in New York City is based on a five-year return period storm, based on historical data from 1903 to 1950, equivalent to approximately 1.75 inches of rainfall in one hour, to size stormwater infrastructure. In some older neighborhoods, systems are designed for a three-year storm event.
For urban areas such as New York City, pluvial flooding occurs when intense rainfall overwhelms the ground or drainage systems, and unlike riverine or coastal flooding, it is not confined to mapped flood zones and can happen anywhere, often with little warning.
Floods are driven by localized cloudbursts, impervious urban surfaces, and aging or undersized infrastructure.
However, these static design assumptions are increasingly misaligned with observed rainfall patterns, as we just saw, and it is not only New York City. Many cities are not built for today’s rainfall extremes, as the intensity of recent rainfall events are overwhelming infrastructure designed for a different era.
Because they’re not tied to a water body, pluvial floods often catch communities off guard, especially in areas not considered high-risk under traditional Federal Emergency Management Agency (FEMA) flood maps. As a result, many residents in these areas do not carry flood insurance, contributing to a significant protection gap. This leaves households financially vulnerable when flooding occurs outside traditional floodplains, a growing reality in cities across the East Coast.
Compound flooding is also a growing threat; flooding in New York City is no longer just about rainfall. When extreme rainfall coincides with high tides, the result is compound flooding, a convergence that significantly increases both the volume and extent of flooding across the city.
Limitations of static flood maps and the insurance gap
Despite increasingly frequent inland flooding, flood insurance coverage remains extremely low in many urban areas, largely due to outdated flood maps and a persistent flood insurance protection gap in areas not officially designated as high-risk.
These static flood risk maps are not designed to capture the dynamic nature of urban flooding caused by extreme rainfall events, and typically represent flood zones based on historical data in river floodplains or coastal storm surge scenarios.
They do not account for short-duration, high-intensity rainfall, changing drainage conditions, or the interaction with sea-level rise and tides. Advanced probabilistic modeling is essential to understand how flood risk evolves in real time and under future scenarios.
Even more than 10 years after Superstorm Sandy in 2012, outdated FEMA Flood Insurance Rate Maps (FIRMs) continue to guide the requirement to purchase flood insurance with a mortgage from a federally regulated lender, putting exposure at risk where it is known to be vulnerable to flooding.
Preliminary FIRMs from 2015 are being used to guide New York City’s building code and floodproofing, except where the effective FIRMs are more restrictive, causing a source of considerable confusion for homeowners.
In the previous week, there were at least four 1-in-1,000-year rainfall events across the United States, including Texas, North Carolina, New Mexico, and Illinois. — all intense deluges that are thought to have roughly a 0.1% chance of happening in any given year. With a clearer understanding of the risk, all stakeholders, including insurers can ensure better mitigation against extreme rainfall and pluvial flooding in the future.
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