GFDL - Geophysical Fluid Dynamics Laboratory

Increase in Atlantic Hurricane Numbers Likely Due to Improvements in Monitoring

Records of Atlantic hurricanes seem to show an increase in storm
frequency since the late 19th century, but research published this week
reveals that the increase in tropical storm and hurricane numbers is
likely due to better observations of short-lived storms.   Improvements
in observational tools and analysis techniques have resulted in more
complete storm monitoring and recording systems. 

A sampling methodology developed by GFDL scientists Gabriel Vecchi and Thomas Knutson takes
into account the possibility of “missing” storms not measured by ships
over the open Atlantic Ocean.  Previously published research by Vecchi
and Knutson (2008, Journal of Climate)
demonstrated that a substantial number of storms would not have been
observed or recorded during the era  when satellites were not available,
and ships were used to record storms (from the late 1800s through the

In this new study, lead author Chris Landsea (NOAA?s National Weather
Service), coauthors Vecchi, Knutson, and Lennart Bengtsson (University
of Reading, UK), analyzed the increase in storm frequency since the 19th
century and show that any increase arises mainly from very short-lived
storms.  Moderate duration storms (lasting more than two days) have not
shown a long-term increase.  The increase in very short-lived storms is
likely due to enhanced monitoring, the authors conclude. 

The resulting time series, with the very short-lived cyclones removed
and estimated number of missed longer-lived cyclones added in, shows no
significant long-term trend.  Although there is no significant increase
in tropical cyclone frequency, their paper, “Impact of Duration
Thresholds on Atlantic Cyclone Counts” (in American Meteorological
Society?s Journal of Climate) does not consider the possible changes in
hurricane strength that may occur in the future, due to global warming. 

Coauthors Gabriel Vecchi and Thomas Knutson discuss this research in an audio podcast.  See a related web page with more information on Historical Changes in Atlantic Hurricane and Tropical Storms.