A nested high-resolution ocean model, based on NEMO-CICE, has been developed to study the position and variability of the Subtropical Front (STF) in the wider New Zealand region. The model grid sizes of about 4km resolve partially sub-mesoscale processes. The finer model mesh improves the oceanic circulation of the East Australian Current (EAC), EAC-Extension (EAC-Ext) and Tasman Front (TF). Without the high resolution nest the EAC-Ext is too stable and transporting too much heat and salt through the Tasman Sea into the Indian Ocean. Consequently, temperature and salinity profiles with the high-resolution nest over the Tasman Sea agree better with observations than without and highlight the importance of mesoscale processes within the EAC-Ext for the cross-shelf transport of heat and salt into the Tasman Sea. The southern-most location of the 11°C isotherm (STF_TEMP) and 34.8 isohaline (STF_SALT) over the top 500m has been used to define the location of the STF, the water mass boundary between subtropical and subantarctic waters. The STF_TEMP (STF_SALT) shifts up to ±4° (±2°) meridionally on seasonal timescales, less in shallower regions. On interannual timescales the meridional shift is around ±1° for STF_TEMP and STF_SALT and linked to changes in the meridional transport of heat and freshwater through the Tasman Sea. Here the transport preference between Pacific and Indian Ocean, either through Indonesian Archipelago or through the Tasman Sea plays an important role. If transports preference is through the Indonesian Archipelago, heat and freshwater content in the Tasman Sea decreases and increases respectively and the STF moves northward.