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Autonomous underwater glider observations collected during and after 2017 Hurricanes Irma, Jose, and Maria show two types of transient response within the Gulf Stream. First, anomalously fresh water observed near the surface and within the core of the Gulf Stream offshore of the Carolinas likely resulted from Irma's rainfall being entrained into the Loop Current-Gulf Stream system. Second, Gulf Stream volume transport was reduced by as much as 40% for about 2 weeks following Jose and Maria. The transport reduction had both barotropic and depth-dependent characteristics. Correlations between transport through the Florida Straits and reanalysis winds suggest that both local winds in the Florida Straits and winds over the Gulf Stream farther downstream may have contributed to the transport reduction. To clarify the underlying dynamics, additional analyses using numerical models that capture the Gulf Stream's transient response to multiple tropical cyclones passing nearby in a short period are needed.

Plain Language Summary In September 2017, Hurricanes Irma, Jose, and Maria impacted the Gulf Stream in rapid succession. Observations collected by an autonomous underwater glider uniquely capture the subsurface structure of the Gulf Stream during this time period, revealing two distinct transient responses of the oceanic western boundary current in the weeks following the storms. Unusually, fresh water within the Gulf Stream off the coast of the Carolinas is attributable to rain from Irma that was entrained in the Loop Current-Gulf Stream system. A reduction in Gulf Stream volume transport by as much as 40% over a period of about 2 weeks likely resulted from the hurricane-related winds over the Gulf Stream. The success of the glider mission and a submarine cable in capturing the Gulf Stream's response to passing storms highlights the need for sustained deployment of ocean observing assets to measure before, during, and after the passage of tropical systems. To clarify the underlying dynamics of the Gulf Stream's transient response to these storms, additional analyses using realistic numerical models are needed.