Numerical modeling of the impact of hurricanes on ocean dynamics: sensitivity of the Gulf Stream response to storm's track

The study is focused on the disruption that a storm can cause to ocean stratification and ocean currents in a region dominated by a western boundary current and meso-scale variability. Sensitivity experiments with a regional numerical ocean model of the US East Coast are used to simulate different hurricane tracks to study the impact on the Gulf Stream (GS) flow, surrounding waters and coastal sea level. Realistic simulations of Hurricane Matthew (October 2016) using surface wind and heat flux from NOAA's operational coupled forecast system were compared with idealized artificial hurricanes with tracks located at different distances from the coast (200-600 km). Despite the limitation of representing realistic wind patterns by an analytical formula, coastal storm surge near the hurricane was simulated quite well. The height of the coastal storm surge was found to be very sensitive to the location of the hurricane track relative to the coast, but the impact of the hurricane on the GS flow was found to be less sensitive to the exact hurricane track, though the maximum influence was when the hurricane track passed 100 km east of the GS with winds over the GS opposing the current direction. Hurricanes that passed within hundreds of kilometers from the GS caused disruption in the GS dynamics and weakening in the downstream flow of the GS that can last for many days after the storm disappeared. This indirect impact of hurricanes on the GS can elevate sea level along long stretches of the coast. The impact of a hurricane on a region dominated by meso-scale variability is complex, creating unpredictable spatial changes in temperatures and currents. After the hurricane disappeared and without additional surface heating, it may take the stratification as much as 2 months to recover to pre-hurricane conditions by advection alone. This lasting impact of a storm on ocean dynamics is consistent with observations that show minor tidal coastal flooding that lasts for days after hurricanes passed offshore.