Water vapour is involved in many atmospheric processes. Precipitation specifically relies on the amount of precipitable water vapour (PWV) or the water vapour content suspended in the atmosphere. Opportunities with regard to the conversion of existing continuous Global Navigation Satellite System (GNSS) stations to GNSS meteorology stations (GNSS MET) with very little cost and acquisition of near real-time water vapour have become popular in studies of the estimation of water vapour using GNSSs. In order to convert the GNSS observables into meteorological assets, one has to account for the extremely important conversion parameters between zenith wet delay and PWV in GNSS meteorology: T-m or Q. They are estimated by analysis of radiosonde profile observations of a radiosonde station (RS). In this study, linear T-m models were estimated from 4103 profile observations of eight Turkish RSs for the year 2011. The verification of these models was tested by using 1 year of observations at the Ankara and Istanbul RS-GNSS stations. A T-m = 48.55 + 0.80T(s) model was computed for Turkey with a root mean square error of +/- 2.57 K. The accuracies of PWV derived from the developed T-m model and the GNSS observations at the Ankara and Istanbul stations in 2013 and 2014 were found to be +/- 1.7 and +/- 1.8 mm, respectively.