Climate of Broome

Broome has a tropical climate with hot and humid summers and warm winters. There are two distinct seasons: the ‘wet’ usually from December to March and the ‘dry’ for the remainder of the year. The median annual rainfall is 532 mm on an average 44 days, although there is considerable variation from year to year.

The two main broadscale influences are the band of high pressure known as the sub-tropical ridge well to the south, and the monsoon which delivers moist air from the warm tropical waters to the north. During the warmer months a heat-trough forms over the inland Kimberley. These combine to produce a general southeasterly wind regime for much of the year. Reliable afternoon sea-breezes arrive from the northwest to southwest during the warmer months.

From October to April maximum temperatures average over 33°C while overnight minima are a typically warm 26°C in the summer months. The highest temperature ever recorded is 44.8°C on 10 December 1951, however the temperature seldom rises above 40°C. By contrast winters are mild, with July average maximum and minimum temperatures being 26.9°C and 12.0°C respectively. Overnight temperatures rarely fall below 5.0°C and only fall below 10°C about once a week during July on average. The lowest temperature ever recorded is 3.3°C on 21 July 1965.

Over 75 % of the average annual rainfall falls from January to March associated with thunderstorms and tropical lows or cyclones. These mechanisms can produce heavy rain in short periods, and often a significant proportion of the yearly total can fall in just one or two days. The unreliable nature of the occurrence and movement of thunderstorms and tropical systems result in rainfall being highly variable. Rainfall during the cooler months is usually associated with cloud bands originating from tropical waters to the northwest. The highest daily fall occurred on 30 January 1997 when 476.6 mm fell. The highest annual total is 1228 mm in 1974 due mainly to heavy rains associated with tropical cyclone Fiona-Gwenda in January.

Tropical cyclones capable of strong winds, high seas and heavy rain can be experienced during the months from November to April, but are most common in January and February. One of the more notable cyclones to affect Broome was that on 19 November 1910. Forty lives were lost, 20 houses totally destroyed and over 70 damaged. The pearling fleet was badly hit with 34 boats sunk and 67 blown ashore. Other significant tropical cyclones occurred in January 1926, March 1935, February 1956, February 1957, January 1964 (Bessie), December 1970 (Eva), February 1984 (Chloe), March 1985 (Lindsay), April 2000 (Rosita) and February 2002 (Chris).

It is not uncommon for very little rain to occur for months on end. The median rainfall for the months of July to October is actually zero. Longer dry periods of over 12 months are associated with the failure of the wet season. One of the driest periods occurred from April 1958 to December 1959 when just 168 mm fell. Other dry periods occurred in 1891, 1924, 1928, 1944, 1990 and 1992.

Evaporation is high. In November the average daily rate is 9.5 mm per day. The relative humidity is generally uniform from month to month averaging about 60 - 70 % at 9 a.m., while at 3 p.m. values range from about 35 % in the cooler months to about 60 % in the wettest months.