This map is generated by querying the Bureau of Meteorology weather API at various locations around Melbourne and returns temperature values. A local Redis cache is used (in case you keep clicking!) to re-use recently fetched data. The scattered data points are interpolated using radial basis functions (this little JavaScript library -- rbf) onto a regular grid (pre-defined via a shapefile) and plotted using D3js. The boundaries of a second shapefile (corresponding to Melbourne,Au ) is used to clip the edges of the scattered grid.
I took inspiration for this years ago from a D3js visualisation of weather observations displayed in the UK which had time-series animation of weather observations going back 100 years or so - which I have long since lost the source and name of the original developer - who did ultimately take down their website and source code.