The temperature records used here are satellite sea surface temperatures. They are provided in several places, and what’s here comes from NOAA, presented as °C in the dataset dhw_5km. This dataset has data from grids 0.05° x 0.05°, corresponding to 5km x 5km.

The closest grid cell to Williamstown beach is centred on Lon. 144.875, Lat. -37.875. Two other snorkelling/diving spots are included; the SE corner of the bay (Blairgowrie, Rye, etc.) is 144.775, -38.375, and just outside Western Port (near Flinders pier) is 145.025, -38.475.

The temperatures are daily measurements, so the graphs are a bit noisy; some other places show temperatures averaged over a few days to smooth things out a bit.

Williamstown time series

Current year, with last year for an immediate comparison

Multi-year plots

The first figure shows the current year, other years from 2014 onwards in the background, and the second includes the past 22 years. The third figure shows the current year against 10- and 20-year averages.

Three places of interest to divers and snorkellers

Open coast sites, such as Flinders, don’t get as warm or as cold as those near the top of Port Phillip Bay (Williamstown). Places near the entrance of the bay (Blairgowrie) are intermediate, but closer to open ocean conditions.

Temperature contour map