Last updated October 10, 2018

Recent increases in U.S. heavy precipitation associated with tropical cyclones

  • Analyzes precipitation time series for 935 long-term U.S. climate stations to identify daily extreme events associated with tropical cyclones (TCs)
  • Defines extremes as daily amounts exceeding a threshold for a 1 in 5-yr occurrence
  • Finds that TCs account for 30% or more of all such extreme events at a number of stations and about 6% of the national annual total
  • Finds that during 1994–2008, the number of TC-associated events was more than double the long-term average while the total annual national number of events was about 25% above the long-term (1895–2008) average
  • Finds that while there has been a recent increase in the number of landfalling U.S. hurricances, the increase in TC-associated heavy events is much higher than would be expected from the pre-1994 association between the two
  • Regional results show there are positive heavy precipitation event index (HPEI) anomalies in all nine regions from 1994–2008, suggesting a multitude of meteorological causes for the overall national anomaly, with TCs making a substantial contribution in four regions:
    • Northeast (73% HPEI anomaly, 32% TC contribution),
    • Central (26%, 51%),
    • South (25%, 48%), and
    • Southeast (40%, 100%)
  • Finds that in the Northeast, Central, and South regions, factors other than TCs make at least an equal contribution to the recent anomalies; however, the Southeast anomaly is solely a result of anomalous TC contributions