Generally speaking, the vertical axis of a tropical cyclone, usually defined by the location of minimum wind or minimum pressure. The cyclone center position can vary with altitude. In advisory products, refers to the center position at the surface.
National Oceanic and Atmospheric Administration's NOAA, National Weather Service, Glossary of NHC Terms, National Centers for Environmental Prediction, National Hurricane Center, Fl, USA 2012. http://www.nhc.noaa.gov/aboutgloss.shtml, (ND/ Hurr Sci - Amer) {146}