When tropical cyclones—storm systems ranging in strength from tropical depressions to major hurricanes—form over the Gulf of Mexico’s warm waters, they have a high chance of causing many deaths as well as widespread property damage in coastal communities. Although accurate predictions of cyclone activity could help reduce such destruction, global models do not yet have a good track record of predicting tropical cyclone formation in this region.
One reason for this deficiency may be because global models have so far proven incapable of capturing the complex relationship between cyclone activity and intraseasonal oscillations in the tropical atmosphere. Also called the Madden-Julian Oscillation, these large-scale wave patterns create eastward propagating pulses of anomalous wind, rainfall, cloud cover, and sea surface temperature variations that typically recur every 30 to 60 days. Despite previous studies indicating that intraseasonal oscillations in the northeastern Pacific Ocean can significantly influence cyclone activity in the western Caribbean Sea and the Gulf of Mexico, dynamic models have so far been unable to accurately reproduce this relationship.
Now Gao et al. evaluate the ability of the Geophysical Fluid Dynamics Laboratory’s latest High Resolution Atmospheric Model (HiRAM) to simulate this relationship on the basis of retrospective seasonal predictions for the 25-year period between 1990 and 2014. Their results indicate that HiRAM successfully captures the influence of intraseasonal oscillations on tropical cyclone activity in the Gulf of Mexico region, including the formation of tropical storms and major hurricanes, as well as those that make landfall.
The authors attribute the model’s success to its realistic representation of large-scale oscillations and moisture variations over the northeastern Pacific during the Northern Hemisphere summer, a finding that lends additional support to the idea that convection in the Gulf of Mexico is strongly influenced by atmospheric variability over the Pacific. HiRAM’s overall success suggests that in the future, it could be used to predict regional tropical cyclone risk for periods ranging from 2 weeks to a couple of months—timescales that could potentially benefit the Gulf of Mexico’s coastal communities. (Journal of Geophysical Research: Atmospheres, https://doi.org/10.1002/2017JD027756, 2017)
—Terri Cook, Freelance Writer