Uncertainties in Tropical-Cyclone Translation Speed
June 6th, 2019
Key Findings
The apparent slowing of tropical cyclones occurs abruptly, rather than gradually, and primarily in the earlier part of the period of record, rather than the later part when the effects of climate change have been accelerating. These factors argue against a dominant role of climate change.
While some of the slowing is associated with natural climate variability much of it may be artificial, due to the introduction of satellite remote sensing in the 1960s.
The conclusions of this study are tentative and will require further research to firm them up. Such research could involve scrutiny of both observations and the output from climate models. In particular, a better understanding of the effects of the introduction of satellite remote sensing in the 1960s on the record of cyclone movement is needed.
A recent study found a downward trend from 1949-2016 in the speed at which tropical cyclones move. If this could be attributed to climate change the implications would be enormous. Slower moving storms, as exemplified by Hurricane Harvey in 2017, have the potential to produce much more rainfall than faster ones.
This study finds that the bulk of the decrease in speed is related to abrupt changes that occur in the earlier part of the period of study. Both the abruptness along with the lack of change during more recent times argues against a dominant role for climate change. The results suggest that the changes are likely due to a combination of natural climate variability and changes over time in the manner in which tropical cyclones were tracked. In particular the introduction of satellite remote sensing in the 1960s may have distorted the record by yielding more observations in areas which had previously been uncharted. It appears that such areas are ones where storms naturally move more slowly.