Here we present the 6-second resolution raw thermosalinograph (TSG) data collected, between 01 November and 14 November 2018, during Voyage 254 on the RS Algoa. A SeaBird SBE45 Thermosalinograph (TSG) is used to opportunistically collect underway near-surface temperature and conductivity measurements during research and monitoring cruises. Water is continuously pumped to the TSG from an intake located in the hull of the vessel, and the observations are continuously interfaced with navigational information. A temperature sensor close to the intake provides temperature measurements of the incoming water (T1). The temperature of the water inside the conductivity cell (T2) is used to accurately compute salinity (S) from the conductivity measurements (C). The West Coast Whale Cruise was conducted on the Algoa Voyage 254 between 1 and 14 November 2018. The cruise operated between the shelf, slope and offshore regions (<2000m depth) off the west coast of South Africa, between Cape Point (-34.36.111, 18.38064) and Groenriviermond (-30.8277, 17.52061). This cruise was undertaken for data collection as part of a collaborative project led by the Department of Environmental Affairs (DEA) in collaboration with the Whale Unit, Mammal Research Institute of the University of Pretoria, Department of Agriculture, Forestry and Fisheries (DAFF), National Oceanic and Atmospheric Administration (USA), Aqualie Institute (Brazil) and Oregon State University (USA). The greater programme is titled 'Large whale research - genetic relatedness, stock identification, abundance, feeding and migratory behaviours' and has two components, the east coast and west coast components. This cruise focused on the west coast humpback whales.