Rapid shelf‐wide cooling response of a stratified coastal ocean to hurricanes

Abstract

Large uncertainty in the predicted intensity of tropical cyclones (TCs) persists compared to the steadily improving skill in the predicted TC tracks. This intensity uncertainty has its most significant implications in the coastal zone, where TC impacts to populated shorelines are greatest. Recent studies have demonstrated that rapid ahead‐of‐eye‐center cooling of a stratified coastal ocean can have a significant impact on hurricane intensity forecasts. Using observation‐validated, high‐resolution ocean modeling, the stratified coastal ocean cooling processes observed in two U.S. Mid‐Atlantic hurricanes were investigated: Hurricane Irene (2011)—with an inshore Mid‐Atlantic Bight (MAB) track during the late summer stratified coastal ocean season—and Tropical Storm Barry (2007)—with an offshore track during early summer. For both storms, the critical ahead‐of‐eye‐center depth‐averaged force balance across the entire MAB shelf included an onshore wind stress balanced by an offshore pressure gradient. This resulted in onshore surface currents opposing offshore bottom currents that enhanced surface to bottom current shear and turbulent mixing across the thermocline, resulting in the rapid cooling of the surface layer ahead‐of‐eye‐center. Because the same baroclinic and mixing processes occurred for two storms on opposite ends of the track and seasonal stratification envelope, the response appears robust. It will be critical to forecast these processes and their implications for a wide range of future storms using realistic 3‐D coupled atmosphere‐ocean models to lower the uncertainty in predictions of TC intensities and impacts and enable coastal populations to better respond to increasing rapid intensification threats in an era of rising sea levels.

Coastal ocean circulation during Hurricane Sandy

“…The observed and modeled offshore bottom velocities, stable water column, momentum balance terms, and temperature diagnostics indicate that mixing processes alone were not sufficient for the seaward progression of the Cold Pool Front ∼70 km offshore ahead of Sandy's landfall in New Jersey. The observed ahead‐of‐eye‐center surface cooling was similar to previous studies of tropical cyclones that impacted the MAB during the stratified season such as Irene [ Glenn et al ., ; Seroka et al ., ] and Barry [ Seroka , ]. However, unlike these previous storms Sandy induced an extreme coastal ocean response to a tropical cyclone with the offshore advection of the Cold Pool Front.…”

Generation of Near‐Inertial Currents on the Mid‐Atlantic Bight by Hurricane Arthur (2014)

“…Longshore winds could generate upwelling or downwelling along the coast. Onshore winds may drive onshore surface currents and offshore bottom currents, and the resulting shear‐induced mixing could lead to rapid ahead‐of‐eye center cooling of the surface mixed layer (Glenn et al, ; Seroka et al, ). Nevertheless, Chen et al () and Chant () reported observations of low‐mode near‐inertial internal waves that are consistent with local wind forcing.…”

Response of Coastal Water in the Taiwan Strait to Typhoon Nesat of 2017

“…Within the past two decades, extensive research on the deep ocean response to typhoons has taken place (e.g., [1][2][3][4][5][6][7]). In contrast, the impact of a typhoon on coastal waters has been relatively less studied (e.g., [8,9]). Coastal waters yield an important influence on the intensity of a typhoon approaching landfall.…”

“…Coastal waters yield an important influence on the intensity of a typhoon approaching landfall. At the same time, a typhoon will also strongly enhance vertical mixing in the near-shore waters, influence volume and heat transport in both along-and cross-shore directions, and alter the marine environment in many ways (e.g., [8,9]). Here, we examine the response examine the response of coastal water in the Taiwan Strait (TWS, Figure 1) following the crossing of Typhoon Nesat in 2017.…”