The Fremantle Doctor, the Freo Doctor, or simply The Doctor is the Western Australian vernacular term for the cooling afternoon sea breeze which occurs during summer months in south west coastal areas of Western Australia. The sea breeze occurs because of the major temperature difference between the land and sea.
The name was in use as early as the 1870s and was similar to equivalent terms for winds that occurred in South Africa and the West Indies.
During summer months, it consistently blows from the southwest along the southern half of the west coast, starting between noon and 3 pm. It can penetrate as far inland as 100 kilometres (60 mi), reaching York in the early evening.
In Perth, the capital city of Western Australia, the wind is named the Fremantle Doctor because it appears to come from the nearby coastal city of Fremantle, and it brings welcome relief from the summertime high temperatures.
The Fremantle Doctor often cools the Perth suburbs by several degrees, whilst nearer the coast the wind can be quite strong, often blowing between 15 and 20 knots and making afternoon beach visits unpleasant.
On days when the wind fails, the afternoon temperatures of Perth suburbs are considerably higher, often exceeding 40 °C (104 °F), although this is also attributable to the influence of a strong easterly wind blowing in hot desert air from the arid interior of the state.
The Fremantle Doctor is strongest in December and January, when the temperature differential between the land and ocean is greatest. In February and March the breeze is not as strong, because the ocean temperature is a bit warmer. Though October and November are not as warm, the ocean temperature is cooler resulting in the sea breeze in these months.
Other months have a weak or non-existent Fremantle Doctor. In the winter months, the land temperature is usually cooler than the ocean temperature, and this sometimes results in the weaker land breeze in the early morning.
When the Fremantle Doctor first arrives it is from the west-south-west (WSW) direction. Later when it is at maximum strength, the direction is usually from the southwest or south-south-west. By the early evening, the direction is from the south. This change in wind direction is due to the Coriolis Effect. Other factors, like the prevailing wind of a particular day, can also have an effect on the direction.
- Christensen, Joseph (2009)Fremantle Doctor page 389 of Gregory, Jenny; Gothard, Janice; Gregory, Jenny; Gothard, Jan (2009), Historical Encyclopedia of Western Australia, University of Western Australia Press, ISBN 978-1-921401-15-2
- Wind roses for selected locations in Australia, Bureau of Meteorology. Retrieved 30 January 2010.
- "Origin of term for the sea breeze in Perth still unknown". Sunday Times: (Perth, W.A.), 23 Feb. 1986, p. 49,
- Masselink, G. (1996). Sea breeze activity and its effect on coastal processes near Perth, Western Australia. Royal Society of Western Australia. Journal of the Royal Society of Western Australia, Vol. 79, part 3 (September 1996) p. 199-205.
- Courtney, Joe; Middelmann, Miriam (2005). "Meteorological hazards" (PDF). Natural hazard risk in Perth, Western Australia – Cities Project Perth Report. Geoscience Australia.