Revisiting Global Tropical Cyclone Statistics in Light of an Active 2017 Season in the Atlantic Basin

In recent decades, there has been a growing tendency by many in the meteorological community (media and scientists) to predict expected seasonal tropical cyclone frequency in the Atlantic Basin. Typically, the numbers are compared to seasonal averages. Although this is of most immediate concern to people in the eastern U.S., it focuses attention on the Atlantic Basin almost exclusively. Further, it often drives climate change discussions to extrapolate Atlantic Basin activity to that experienced around the globe.

Given the decreased tropical cyclone activity in the Atlantic in recent years, these predictions (which were much more dire in the mid-2001-2010 decade when Atlantic activity was high) have tended to soften. Then came the 2017 Atlantic season and attention immediately refocused on a growing hurricane risk. Yet, overall, global numbers of hurricanes remain relatively constant (as they have since the 1950’s).

We have studied tropical cyclones globally to ascertain if the Atlantic frequency changes are linked to any global changes. To do this, we collected data from weather agencies around the world and tried to present findings in a way that was as unbiased as possible. While there were inconsistencies across the various datasets, especially in regard to the storm's wind data, we were still able to construct a realistic global cyclone database. Based on our analyses, we have concluded that high activity levels in one basin are often balanced by low activity in others. The Atlantic - Eastern Pacific couplet is only one such example. This paper will serve as an update to our previous work in which we described our early efforts. At that time, we found, on average, 70 named tropical cyclones worldwide. In both this and our original study, we did not address the issue of naming short-lived tropical systems, which we found to be inconsistent across ocean basins worldwide. Our results suggest, that from a global climate change perspective, there is NOT a growing NUMBER of tropical cyclones and that hurricane strength globally (Ryan Maue's Accumulated Cyclone Energy studies) is on the decline. We have discovered a marked discontinuity in ACE in the late 1990's (from increasing to decreasing numbers globally). This trend line continued in 2014. Because hurricane assessment is such an important topic in the U.S. and around the world, we also plan to discuss some new ideas for addressing hurricane/tropical cyclone trends and other analytics.