The Bloomberg administration on Monday issued new warnings about New York City’s vulnerability to climate change, offering updated data to encourage businesses, residents and perhaps even future mayors to better prepare against hotter weather, fiercer storms and increased rainfall.

Administration officials estimated that more than 800,000 city residents will live in the 100-year flood plain by the 2050s. That figure is more than double the 398,000 currently estimated to be at risk, based on new maps the Federal Emergency Management Agency released Monday.

Many more businesses and jobs will also be at risk.

The data was released a day before Mayor Michael R. Bloomberg was to issue a report on how the city can better prepare for major weather events, including those like Hurricane Sandy.

Administration officials said that between 1971 and 2000, New Yorkers had an average of 18 days a year with temperatures at or above 90 degrees. By the 2020s, that figure could be as high as 33 days, and by the 2050s, it could reach 57, according to data collected by the New York City Panel on Climate Change.