Specific Heat of Vapour in Convection Formulas

Yes, the Specific Heat of Vapour, measured in Specific Heat Capacity can be negative.

Specific Heat of Vapour is usually measured using the Joule per Kilogram per K[J/(kg*K)] for Specific Heat Capacity. Joule per Kilogram per Celcius[J/(kg*K)], Kilojoule per Kilogram per K[J/(kg*K)], Kilojoule per Kilogram per Celcius[J/(kg*K)] are the few other units in which Specific Heat of Vapour can be measured.