Modulation of Tropical Cyclone Tracks and Rainfall by the North Atlantic Oscillation

Understanding and quantifying the large-scale environmental control of spatio-temporal tropical cyclone (TC) variability beyond a few weeks remains a challenge with significant implications for societal impacts. This study focuses on the relationship between the North Atlantic Oscillation (NAO) and year-to-year changes in TC activity and rainfall using observational data and reanalysis products. We use Poisson regression models to show that low-frequency NAO (LF-NAO) variability is associated with a distinct pattern of TC activity, which extends across the western North Atlantic, the Caribbean Basin, and the Gulf of Mexico. The negative LF-NAO phase is characterized by enhanced TC activity: an interquartile range decrease in the NAO corresponds to a 30%-40% increase in TC track density. While the NAO is known to affect the weather regimes of the mid-latitudes, we show that its low-frequency component has a strong correlation to the large-scale environment across the Main Development Region of TCs. The negative LF-NAO phase is associated with two favorable environmental conditions for TCs: significantly higher sea-surface temperature and weaker deep-tropospheric wind shear. The LF-NAO relationship to TC activity is strongest during El Nino Southern Oscillation positive or neutral conditions and during the negative Atlantic Multidecadal Oscillation phase, and it can also be detected in the basin-scale variations of TC rainfall. By developing annual TC rainfall composites from satellite data and reanalysis products, we show that TC rainfall is strongly enhanced in the Caribbean and in the Gulf of Mexico during the negative LF-NAO phase.