Impact of a warm ocean Eddy's circulation on hurricane-induced sea surface cooling with implications for hurricane intensity

Abstract

Upper oceanic heat content (OHC) in advance of a hurricane is generally superior to prestorm sea surface temperature (SST) for indicating favorable regions for hurricane intensification and maintenance. OHC is important because a hurricane's surface winds mix the upper ocean and entrain cooler water into the oceanic mixed layer from below, subsequently cooling the sea surface in the region providing heat energy to the storm. For a given initial SST, increased OHC typically decreases the wind-induced sea surface cooling, and a warm ocean eddy (WCR) has a higher OHC than its surroundings, so conditions typically become more favorable for a hurricane to intensify when the storm's core encounters a WCR. When considering hurricane intensity, however, one often-neglected aspect of aWCR is its anticyclonic circulation. This circulation may impact the location and magnitude of the hurricane-induced sea surface cooling. Using an ocean model, either prescribed hurricane wind stress or wind stress obtained via coupling to a hurricane model is applied to an initial ocean condition in which the SST is homogeneous, but a WCR is embedded in an otherwise horizontally homogeneous subsurface density field. Based on model experiments, when a WCR is located to the right of the storm track (in the Northern Hemisphere), the interaction of the WCR's circulation with the hurricaneinduced cold wake can cause increased sea surface cooling under the storm core and decreased storm intensity relative to the scenario where no WCR is present at all. Therefore, the presence of a WCR in advance of a hurricane sometimes creates a less favorable condition for hurricane intensification. © 2013 American Meteorological Society.