The predictability of tropical cyclogenesis examined through ensemble data assimilation experiments for Hurricane Karl (2010)

The Pre-depression Investigation of Cloud Systems in the Tropics (PREDICT) field campaign operated 25 flight missions through eight Atlantic tropical disturbances in 2010 to test a set of hypotheses regarding how hurricanes form from easterly waves. The targeted weather systems include cases in which tropical cyclogenesis occurred or failed to occur under conditions that were favorable for development. In this study, an ensemble Kalman filter (EnKF) is applied for examining the genesis of Hurricane Karl (2010) using analyses that include and exclude PREDICT dropsonde observations. Flight missions through this disturbance span five days, thus providing an excellent case study for exploring the impact of observations in modeling the characteristics of the near wave environment. Ensemble forecasts initialized days in advance of the eventual hurricane formation have little skill in capturing the true timing of genesis; nevertheless, the forecast skill improves greatly by the time of the last PREDICT flight mission. This study evaluates the dynamics of the evolving system in an attempt to explain the observed changes in forecast error and ensemble-estimated uncertainty during the cycling data assimilation experiments. The dynamic and thermodynamic structure of the simulated genesis events are evaluated using the same tropical cyclogensis paradigm that motivated the original PREDICT mission.