If the temperature remains 30 ° C and the dew point rises to 25 ° C ( 77 ° F ) , the humidex rises to 42 .
Note how humidex is a dimensionless number , but it indicates an approximate temperature in ° C . If the temperature remains 30 ° C and the dew point rises to 25 ° C ( 77 ° F ) , the humidex rises to 42 .