The authors also found that more intense atmospheric rivers (AR-4 and AR-5) are less common than weaker events, with AR-5 events occurring only once every two to three years when globally averaged. The most intense atmospheric rivers are also less likely to make landfall, and when they do, they are unlikely to maintain their strength for long and penetrate farther inland. "They tend to dissipate soon after landfall, leaving their impacts most felt in coastal areas," said Guan.
The study found four "centers," or hotspots, of where AR-5s tend to die, in the extratropical North Pacific and Atlantic, Southeast Pacific, and Southeast Atlantic. Cities on the coasts within these hotspots, such as San Francisco and Lisbon, are most likely to see intense AR-5s make landfall. Midlatitudes in general are the most likely regions to have atmospheric rivers of any rank.
Strong El Niño years are more likely to have more atmospheric rivers, and stronger ones at that, which is noteworthy because NOAA has recently forecasted that an El Niño condition is likely to develop by the end of the summer this year.
https://phys.org/news/2023-03-world-atmospheric-rivers-intensity-hurricanes.html
