Predictability of North Atlantic tropical cyclone track density

January 22, 2015
Hurricane storm track
Observed and simulated genesis (dots) and tracks (lines) of tropical cyclones that reached hurricane intensity in year 2005 – the most active season on record. Black dots and curves are for observations, and dots and curves of blue, green, and red colors are for the three members of the simulations by the GFDL High Resolution Atmospheric Model. Note that the three runs simulate similar hurricane counts (13, 14, 13) that are close to observations (15), but there is considerable spread in their simulated tracks.

Tropical cyclones are among the most devastating storms on Earth. Tropical cyclone activity in the North Atlantic displays large interannual variability in both number and track density. Recent studies show that global high-resolution models have remarkable skill in simulating the interannual variability in cyclone counts, implicating strong control by sea surface temperatures patterns. This study analyzes an ensemble simulation by the GFDL High Resolution Atmospheric Model, with each member differing only in initial conditions. While previous studies focus on ensemble mean variability due to sea surface temperature forcing, this study examines atmospheric internal variability that affects cyclone track distributions.     

The analysis of the ensemble mean shows that cyclone track density is influenced by changes in local and remote sea surface temperatures. For example, an anomalous sea surface warming over the tropical North Atlantic is favorable for more frequent cyclone passages over most of the basin. The sea surface temperature-forced track density also exhibits inter-basin oscillations. For instance, when cyclones are anomalously active over the Gulf of Mexico, the US East Coast and the open ocean to the east most likely experience a quiet hurricane season. In contrast to strong sea surface temperature control on basin counts, unpredictable internal variability in track density is strong over the Gulf Coast and US East Coast - indicating that prediction of regional cyclone activity, especially landfall hurricanes, is challenging. 

Written by 
Wei Mei, Scripps Institution of Oceanography

Wei Mei1, Shang-Ping Xie1, and Ming Zhao2,3

1Scripps Institution of Oceanography

2NOAA Geophysical Fluid Dynamics Laboratory

3University Corporation for Atmospheric Research