DATE/TIME: Friday, March 27, 2026, 2:30 pm PLACE: ENR building, room 223 or this Remote Live option.
Tyler Janoski
NOAA-EPP Cooperative Science Center for Earth System Science & Remote Sensing Technologies Center
The Physical Drivers and Synoptic Pathways of NYC Flash Floods
Extreme rainfall and subsequent flash flooding are among the greatest weather hazards in New York City. Hurricane Ida underscored these perennial threats in September 2021 when it produced record-breaking hourly rainfall, leading to the death of 13 New Yorkers. To improve our forecasting capabilities, we must strengthen our understanding of the physical mechanisms that enable such extreme events.
The first part of this talk focuses on Ida, where we used NOAA’s Warn-on-Forecast System (WoFS) to conduct ensemble sensitivity analyses (ESA) and other diagnostic techniques to identify key predictors of NYC rainfall. We find that the critical atmospheric conditions for the high rain rates during Ida were the coincident location of the warm front, low-topped supercell activity, and synoptic moisture flux convergence. The ESA also shows that the spread in initial conditions can, within specific circulation patterns, determine the ensemble variability of the WoFS precipitation forecast.
The second part of the talk extends beyond Ida towards a comprehensive flash-flood framework for NYC. Using flash-flood events from the NOAA Storm Events Database and ERA5 reanalysis output to train self-organizing maps, we quantify the risk of flash-flood exposure across various synoptic setups and explore the relative roles of moisture and synoptic forcing. Although we can identify several distinct synoptic types of NYC flash floods, they can occur under a wide range of synoptic conditions. Additionally, we investigate the association between NYC flash floods and tropical cyclones/remnants.
Together, these efforts highlight complementary paths to improving flash flood prediction. WoFS offers detailed insight into storm- and mesoscale processes, while SOMs place individual events like Ida within the broader set of synoptic conditions that have historically produced flooding in NYC. These analyses, combined, provide a clearer picture of the environments that pose the greatest flood risk to urban areas.
Seminar Host:
Tony Broccoli
Department of Environmental Sciences, SEBS, Rutgers University