Surface Cold Pools in the Outer Rainbands of Tropical Storm Hanna (2008) Near Landfall

Surface mesonet observations were used to document the structure of prominent cold pools associated with twoconvectiveouterrainbandsofTropicalStormHannaon5September2008.Thedevelopingrainbandswere located ;400 kmnorth ofthestormcenterastheycrossedtheCarolinacoastlineandpassedover themesonet. The combination of moderate CAPE, moderate low-level cross-band vertical shear, and dry midlevel air provided an environment supportive of surface cold pool formation and long-lived quasi-linear convection. Both rainbands exhibited multiple outward-tilting convective cells and discrete line segments centered within a narrow zone of nearly continuous stratiform precipitation. The mesonet observations provided a unique along- and cross-band perspective of discrete cold pools situated beneath andbehind the convection portions of each rainband.Prominentcold pools extended 40‐80 km behind the rainband’s leading edge and exhibited maximum potential temperature, mixing ratio, and equivalentpotentialtemperaturedeficitsof2‐4 K,1‐2 g kg 21 ,and4‐10 K,respectively.Inthecross-banddirection, convergence of storm-relative inflow along the cold pool leading edge was coincident with a modest high pressure anomaly, while inflow divergence prevailed through the cold pool and rainfall maxima. Several cold pools expanded along-band while being advected downband by the prevailing cyclonic flow. Cold pool wakes were observed more than 50 km behind the rainband leading edge and up to 20 km downband from intense convection.Variations in cold pool intensitywerenotwell correlated with convectiveintensity, rainfallrate,or the degree of midlevel dryness. Implications of prominent cold pools on tropical cyclone convection, size, and intensity are discussed.