Enhanced Ahead-of-Eye TC Coastal Ocean Cooling Processes and their Impact on Air-Sea Heat Fluxes and Storm Intensity
Gregory N Seroka1, Travis N Miles1, Scott M Glenn2, Yi Xu3, Robert Forney1, Hugh Roarty1, Oscar Schofield4 and Josh T Kohut1, (1)Rutgers University, Marine and Coastal Sciences, New Brunswick, NJ, United States, (2)Rutgers University New Brunswick, New Brunswick, NJ, United States, (3)Rutgers University, East Brunswick, NJ, United States, (4)Rutgers University, Department of Marine and Coastal Sciences, New Brunswick, NJ, United States
Abstract:
Any landfalling tropical cyclone (TC) must first traverse the coastal ocean. TC research, however, has focused over the deep ocean, where TCs typically spend the vast majority of their lifetime. This paper will show that the ocean’s response to TCs can be different between deep and shallow water, and that the additional shallow water processes must be included in coupled models for accurate air-sea flux treatment and TC intensity prediction. The authors will present newly observed coastal ocean processes that occurred in response to Hurricane Irene (2011), due to the presence of a coastline, an ocean bottom, and highly stratified conditions. These newly observed processes led to enhanced ahead-of-eye SST cooling that significantly impacted air-sea heat fluxes and Irene’s operationally over-predicted storm intensity.
Using semi-idealized modeling, we find that in shallow water in Irene, only ~6% of cooling due to air-sea heat fluxes, ~17% of cooling due to 1D vertical mixing, and ~50% of cooling due to all processes (1D mixing, air-sea heat fluxes, upwelling, and advection) occurred ahead-of-eye—consistent with previous studies. Observations from an underwater glider and buoys, however, indicated 75-100% of total SST cooling over the continental shelf was ahead-of-eye. Thus, the new coastal ocean cooling processes found in this study must occur almost completely ahead-of-eye.
We show that Irene’s intense cooling was not captured by basic satellite SST products and coupled ocean-atmosphere hurricane models, and that including the cooling in WRF modeling mitigated the high bias in model predictions. Finally, we provide evidence that this SST cooling—not track, wind shear, or dry air intrusion—was the key missing contribution to Irene’s decay just prior to NJ landfall. Ongoing work is exploring the use of coupled WRF-ROMS modeling in the coastal zone.
