Various embodiments include a system having: a computing device configured to monitor a gas turbine (GT) by: determining a moisture content and/or an oxygen content of inlet air entering the inlet of the GT compressor section; determining a corresponding one of the moisture content and/or the oxygen content of exhaust gas from the GT turbine section; calculating a flow rate of the exhaust gas from the turbine section and a flow rate of the inlet air entering the inlet of the compressor section based upon the moisture content and/or the oxygen content of the inlet air and the exhaust gas; and calculating a temperature of the exhaust gas and an energy of the exhaust gas from the turbine section based upon the flow rate of the exhaust gas from the turbine and the flow rate of the inlet air entering the inlet of the compressor section.