Three variants of a one-dimensional coastal polynya model, forced by data from a nearby automatic weather station, are used to examine wintertime ice concentration fluctuations in a coastal polynya at Terra Nova Bay, Antarctica. It has long been believed that the Terra Nova Bay polynya opens in response to strong offshore katabatic wind forcing. This study shows that the sensible and longwave heat fluxes share equally in controlling polynya extent fluctuations, and together, these two terms in the energy budget can explain up to ~50% of the observed variance in open water fraction. Moreover, this study shows that the wind speed becomes important to the polynya dynamics through amplification of the longwave flux. Finally, this study suggests that local katabatic winds at Terra Nova Bay combined with regional ice conditions set up by winds blowing across the Ross Ice Shelf control the fluctuations in Terra Nova Bay polynya extent. ¿ 1999 American Geophysical Union