Observations of the structure and evolution of Hurricane Edouard (2014) during intensity change: Relationship between the thermodynamic structure and precipitation

This presentation focuses on the precipitation evolution and thermodynamic changes that occur on the vortex-scale throughout the life cycle of Hurricane Edouard (2014), in particular during four periods in which NOAA and NASA (HS3) observations are available; one period while Edouard was a slowly intensifying tropical storm, another while a more rapidly intensifying hurricane, during the initial stages of weakening after reaching peak intensity, and later while experiencing moderate weakening in the midlatitudes. Results suggest that, in a shear-relative framework, a wavenumber-1 asymmetry exists whereby the downshear quadrants consistently exhibit the greatest precipitation (deep convection) coverage and highest relative humidity, while the upshear quadrants (particularly upshear right) exhibit relatively less precipitation coverage and lower humidity, particularly in the midtroposphere. Whether dynamically- or precipitation-driven, the relatively dry layers upshear appear to be ubiquitously caused by subsidence. This precipitation and thermodynamic asymmetry is observed throughout the intensification and later weakening stages, while a consistently more symmetric distribution is only observed when Edouard reaches peak intensity. The precipitation distribution, which is also discussed in the context of the boundary layer thermodynamic properties, is intimately linked to the thermodynamic symmetry, which becomes greater as the frequency, areal coverage, and, in particular, rainfall rate increases upshear. Although shear is generally believed to be detrimental to intensification, observations in Edouard also indicate that subsidence warming from mesoscale downdrafts in the low to midtroposphere very near the center may have contributed favorably to organization early in the intensification stage.