An evaluation of thermodynamic estimates of climatological maximum potential tropical cyclone intensity

This paper investigates the performance of two recently developed thermodyn amic models of maximum tropical cyclone intensity (K. A. Emanuel's referred to here as El and G. J. Holland's referred to here as H1), which are desig ned to estimate the most intense storm possible given the ambient environme ntal conditions. The study involves estimating the maximum potential tropic al cyclone intensity (MPI) from climatological information in three ocean r egions, where relatively reliable atmospheric soundings and tropical cyclon e intensity data exist. The monthly MPI was estimated for 28 locations acro ss the northwest Pacific, southwest Pacific, and North Atlantic Ocean regio ns. Empirically derived relationships between observed maximum storm intens ity and sea surface temperature were also utilized in the examination of re gional MPI model performance. Derived MPIs generally agreed well with observed maximum intensities during the tropical cyclone season. The H1 model tended to underestimate the maxi mum intensity of storms early and late in the tropical cyclone season and a t stations between 10 degrees and 20 degrees N in the northwest Pacific, wh ere the effect of continental air led to weak model estimates for the given surface energy conditions. Additionally, extremely intense H1 estimates we re predicted at some stations in the Australian/southwest Pacific region wh ere particularly unstable atmospheric conditions and low ambient surface pr essure values are observed. These features of model performance are largely due to the sensitivity of H1 to warm environmental upper-level temperature s. The El model displayed a poor seasonality, frequently predicting the occ urrence of storms during winter months. Emanuel MPI estimates were at times underestimated for stations in the North Atlantic and northwest Pacific. T he El model estimates in the northwest Pacific were affected by particularl y warm upper-level conditions, while relatively high ambient surface pressu res in the North Atlantic at 25 degrees N lead to MPI estimates, which are weaker than observed in this region.