| Popis: |
The average speed of tropical cyclone (TC) translation has slowed since the mid 20th century. Here we report that North Atlantic (NA) TCs have become increasingly likely to “stall” near the coast, spending many hours in confined regions. The stalling is driven not only by slower translation, but also by an increase in abrupt changes of direction. We compute residence-time distributions for TCs in confined coastal regions, and find that the tails of these distributions have increased significantly. We also show that TCs stalling over a region result in more rain on the region. Together, increased stalling and increased rain during stalls imply increased coastal rainfall from TCs, other factors equal. Although the data are sparse, we do in fact find a significant positive trend in coastal annual-mean rainfall 1948–2017 from TCs that stall, and we verify that this is due to increased stalling frequency. We make no attribution to anthropogenic climate forcing for the stalling or rainfall; the trends could be due to low frequency natural variability. Regardless of the cause, the significant increases in TC stalling frequency and high potential for associated increases in rainfall have very likely exacerbated TC hazards for coastal populations. Tropical cyclone (TC) translation speeds are slowing, increasing the potential for the storms to stall and drop heavy rains on coastal regions. Timothy Hall of NASA Goddard Institute for Space Studies and James Kossin of NOAA National Centers for Environmental Information develop a stall metric and apply it to North Atlantic TCs. They confirm that translation speed is trending downward and show an increasing tendency for North Atlantic TCs to abruptly change direction. Due to this behavior, the fraction of TCs spending more than 48 h over North American coastal regions has increased since the mid-20th Century. Annual-mean rainfall from stalling TCs is more variable than those that do not stall, but has also significantly increased. The combined increase in stall frequency and accumulated rains represents a growing hazard for coastal populations. |
