  The Indian Summer Monsoon (ISM) and the West African Monsoon (WAM) are
dominant drivers of boreal summer precipitation variability in tropical and
subtropical regions. Although the regional precipitation dynamics in these two
regions have been extensively studied, the intraseasonal interactions between
the ISM and WAM remain poorly understood. Here, we employ a climate network
approach based on extreme rainfall events to uncover synchronously occurring
extreme rainfall patterns across the two monsoon systems. We reveal strong
synchronization of extreme rainfall events during the peak monsoon period in
July and August, linking heavy rainfall over North India to that over the Sahel
with a lag of around 12 days. We find that La Ni\~na-like conditions in
combination with the Boreal Summer Intraseasonal Oscillation and an enhanced
Tropical Easterly Jet (TEJ) foster the synchronization between the ISM and the
WAM. Convective clouds are transported by an intensified TEJ from southwestern
Asia toward North Africa, supporting anomalous deep convection over the Sahel
region.
