| Flight-level aircraft data and microwave imagery are analyzed to investigate hurricane secondary eyewall formation and eyewall replacement cycles (ERCs). This work is motivated to provide forecasters with new guidance for predicting and better understanding the impacts of ERCs. A Bayesian probabilistic model that determines the likelihood of secondary eyewall formation and a subsequent ERC is developed. The model is based on environmental and geostationary satellite features. A climatology of secondary eyewall formation is developed; a 13% chance of secondary eyewall formation exists when a hurricane is located over water, and is also utilized by the model. The model has been installed at the National Hurricane Center and has skill in forecasting secondary eyewall formation out to 48 h.;Aircraft reconnaissance data from 24 ERCs are examined to develop a climatology of flight-level structure and intensity changes associated with ERCs. Three phases are identified based on the behavior of the maximum intensity of the hurricane: intensification, weakening and reintensification. Despite a large oscillation of intensity, with a weakening of ∼10 m s-1 occurring during most of the ERC, the net intensity change is near zero. However, a broadening of the wind field is observed, and the eye rarely contracts back to the radius prior to the ERC. The expanding storm size increases the storm's integrated kinetic energy.;Thermodynamic fluctuations are also documented during an ERC. Flight-level temperature, dewpoint, relative humidity, and thetae are all found to increase within the inner-core over the course of an ERC, except for a decrease of mean relative humidity in the moat region. Near the end of an ERC, high values of inertial stability are associated with the relict inner eyewall circulation and create a "containment vessel" that confines the old-eye air mass. This is evident by the difference in thetae values (> 10 K) between the old-eye air mass and the adjacent moat at the end of and following an ERC. The relict inner eyewall circulation is found to be an important feature that can impact the secondary circulation of the inner-core, the intensification of the outer eyewall, and the pressure-wind relationship of the storm. |
