It is well known that tropical cyclones are initiated by warm-core structures. Despite the obvious importance of these warm-core structures, their development is not well understood. Since it has been shown that most Atlantic tropical cyclones are initiated from African easterly waves which have been observed to possess a cold-core structure, this study will examine how the easterly waves transform into warm-core structures. A detailed analysis will be made of the African easterly wave structures which occurred during the Atlantic tropical cyclone season of 1995. The analysis will be based on U.K. Meteorological Office Unified Model global analyses and limited area mesoscale forecasts, together with radiosonde data and Meteosat satellite imagery. The structures of the African easterly waves leaving the West African coast will be closely examined together with their evolution over the ocean. Causal mechanisms for the generation of warm-core structures will be identified.