The Relationship Between the Saharan Air Layer, Convective Environmental Conditions, and Precipitation in Puerto Rico

The Saharan Air Layer (SAL) is a hot, dry, and dust‐laden feature that advects large concentrations of dust across the Atlantic annually to destination regions in the Americas and Caribbean. However, recent work has suggested the SAL may be a contributing factor to high‐impact drought in the Caribbean basin. While the SAL's characteristic dust loadings have been the focus of much previous research, fewer efforts have holistically engaged the co‐evolution of the dust plume, its associated convective environment, and resultant rainfall in Caribbean islands. This study employs a self‐organizing map (SOM) classification to identify the common trans‐Atlantic dust transport typologies associated with the SAL during June and July 1981–2020. Using the column‐integrated dust flux, termed integrated dust transport (IDT), from MERRA‐2 reanalysis as a SAL proxy, the SOM resolved two common patterns which resembled trans‐Atlantic SAL outbreaks. During these events, the convective environment associated with the SAL, as inferred by the Gálvez‐Davison Index, becomes less conducive to precipitation as the SAL migrates further away from the west African coast. Simultaneously, days with IDT patterns grouped to the SAL outbreak typologies demonstrate island‐wide negative precipitation anomalies in Puerto Rico. The SOM's most distinctive SAL outbreak pattern has experienced a statistically significant increase during the 40‐year study period, becoming roughly 10% more frequent over that time. These results are relevant for both climate scientists and water managers wishing to better anticipate Caribbean droughts on both the long and short terms. Plain Language Summary Saharan dust can be mobilized, lofted, and transported astonishingly vast distances from its African source regions to destinations in the Caribbean and Americas. While the movement of the dust through the atmosphere has important implications for ecological productivity and global climate trends, it can also acutely suppress tropical rainfall as it traverses the western Atlantic. This study finds that days with the most prominent extensions of Saharan dust toward the Caribbean were also less favorable for thunderstorm activity over the Atlantic Ocean and resulted in island‐wide below‐average rainfall in Puerto Rico. Additionally, the most prominent SAL outbreak days have become roughly 10% more common since 1981. Key Points Saharan air layer (SAL) patterns are resolved by a self‐organizing map of daily column‐i