Shape of Atlantic Tropical Cyclone Tracks and the Indian Monsoon

Abstract

We find a significant enhancement of the North Atlantic subtropical high on interannual timescales (1970–2016) concurrently linked to an anomalously strong Indian monsoon in September. Consistent with a stronger North Atlantic subtropical high, enhanced anticyclonic flow and subtropical easterlies in the eastern Atlantic basin are found during strong monsoon years. Observational regression analysis combined with a statistical track model are used to assess the influence of these monsoon-linked wind variations on Atlantic tropical cyclone (TC) tracks originating in the main development region. When controlling for effects of El Niño–Southern Oscillation (ENSO), a westward shift of TC tracks is shown to be robustly correlated to internal monsoon variability in September. This work highlights variability of the Indian monsoon as an additional constraint on Atlantic TCs, with increased landfall probability during a strong monsoon. Previous attribution of similar steering effects to ENSO need to be reconsidered to account for ENSO's correlation with the monsoon.