Previous research has noted that high surface temperatures within certain "offensive" air masses can lead to increased mortality. This study assesses the relationship between daily mortality rates and weather within the city of Shanghai, China, while introducing an operational heat/health warning system for the city. Using numerous meteorological observations, the spatial synoptic classification has been used to classify each summer day from 1989 to 1998 into one of eight air mass types for Shanghai. Through the comparative analysis of the daily air mass type and the corresponding Shanghai mortality rate, "moist tropical plus" (MT+), an extremely hot and humid air mass, was identified as an offensive air mass with the highest rates of mortality. Using stepwise regression, an algorithm was produced to help predict the number of excess deaths that will occur with each occurrence of the MT+ airmass. The heat/health warning system was run experimentally in the summer of 2001 and illustrated that the use of a warning system can alert the city's residents of potentially offensive weather situations that can lead to a deterioration in human health.