Often, people mistake nor'easters for tropical cyclones and do not differentiate between the two weather systems. Nor'easters differ from tropical cyclones in that nor'easters are cold-core low-pressure systems, meaning that they thrive on drastic changes in temperature of Canadian air and warm Atlantic waters. Tropical cyclones are warm-core low-pressure systems, which means they thrive on purely warm temperatures. However, in rare cases, such as the 1991 Perfect Storm, a small tropical cyclone can develop inside the warm seclusion of an intense nor'easter if the sea surface temperatures are sufficiently warm.