Janoski et al. (2025) The Physical Mechanisms of Hurricane Ida’s Extreme Rainfall in New York City: Insights from the Warn-on-Forecast System

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Identification

• Journal: Weather and Forecasting
• Year: 2025
• Date: 2025-11-07
• Authors: Tyler Janoski, James F. Booth, Thomas J. Galarneau
• DOI: 10.1175/waf-d-25-0098.1

Research Groups

National Oceanic and Atmospheric Administration (NOAA) National Severe Storms Laboratory (NSSL)

Short Summary

This study investigates the atmospheric processes across multiple spatial scales responsible for the record-breaking hourly rainfall in New York City during the remnants of Hurricane Ida. It finds that low-topped supercells, influenced by synoptic circulation, low-level jet strength, and warm front position, produced the highest rainfall rates.

Objective

• To examine the role of atmospheric processes across synoptic, meso-, and convective scales in producing the extreme hourly rainfall rates experienced in New York City during the remnants of Hurricane Ida on 1–2 September 2021.

Study Configuration

• Spatial Scale: New York City and the surrounding region affected by the remnants of Hurricane Ida, with analysis spanning synoptic, mesoscale, and convective scales.
• Temporal Scale: 1–2 September 2021, focusing on the record-breaking hourly rainfall event from 01:00 to 02:00 UTC on 2 September.

Methodology and Data

• Models used: NOAA National Severe Storms Laboratory’s Warn-on-Forecast System (WoFS), an ensemble forecast and data assimilation system.
• Data sources: Not explicitly detailed, but implied to be assimilated into the WoFS ensemble forecast system.
• Analysis techniques: Ensemble sensitivity analysis, direct comparison of wettest and driest ensemble members, and a newly implemented front-detection algorithm.

Main Results

• Low-topped supercells embedded within the remnants of Hurricane Ida were responsible for the highest rainfall rates in New York City.
• The number and trajectory of these supercells were significantly influenced by the synoptic circulation, which dictated the steering flow.
• The strength of the low-level jet played a crucial role by transporting tropical moisture and instability towards the slow-moving warm front.
• Rainfall rates in New York City were highly sensitive to the strength and precise position of the warm front; variations in its placement could shift the maximum precipitation away from the city.

Contributions

• Provides a detailed exploration of the physical mechanisms, previously underexplored, behind the record-breaking rainfall in New York City during Hurricane Ida's remnants.
• Identifies critical features at synoptic, mesoscale, and convective scales that are essential for improving the predictability of future extreme rainfall events.
• Introduces and applies a new front-detection algorithm to analyze supercell trajectories.

Funding

Not specified in the provided text.

Citation

@article{Janoski2025Physical,
  author = {Janoski, Tyler and Booth, James F. and Galarneau, Thomas J.},
  title = {The Physical Mechanisms of Hurricane Ida’s Extreme Rainfall in New York City: Insights from the Warn-on-Forecast System},
  journal = {Weather and Forecasting},
  year = {2025},
  doi = {10.1175/waf-d-25-0098.1},
  url = {https://doi.org/10.1175/waf-d-25-0098.1}
}

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