Big Bank Shoals of the Timor Sea
An environmental resource atlas

The climate of the region is tropical with two distinct seasons: the Northwest Monsoon and the Southeast Monsoon. The Northwest Monsoon season occurs from November to March (i.e. the southern summer) and the Southeast Monsoon occurs from April to September (i.e. the southern winter). Brief transitional periods occur in April and September/October.

Rainfall

The rainfall within the region is monsoonal, with high rainfall associated with the Northwest Monsoon and low rainfall associated with the Southeast Monsoon. Heavy rainfalls are also associated with tropical cyclones and thunderstorm activity.

Cyclones

Tropical cyclones form south of the equator, in the general area of the eastern Indian Ocean and in the Timor and Arafura Seas. An analysis of the Bureau of Meteorology cyclone records, dating back to 1964, indicates that most cyclones approach the area from the east-northeast. Since 1964 an average of 2.6 cyclones per year have occurred in the region bounded by 5^oS to 16.5^oS and 121^oE to 132^oE.

The majority of cyclones occur between December and April. Most
(75 percent) of these cyclones are not fully mature, having an estimated wind speed of less than 80 km/hr. Severe cyclones, with wind speeds exceeding 100 km/hr occur, on average, once every 2.6 years.

Air temperatures

The average mean air temperature is about 28^oC and there is little variation in this. The variation recorded at the Jabiru Oil Field (1983-1993) was from 28.3^oC in summer to 27.0^oC in winter.

Relative humidities

The highest humidities occur from October to May, corresponding to the Northwest Monsoon season. Lower humidities exist during the Southeast Monsoon season because the air mass is of continental origin.

Winds

Two distinct wind regimes are associated with the monsoons; a steady south-easterly airflow originating over the Australian mainland during the Southeast Monsoon, and a steady, moist, west to northwest wind during the summer months or Northwest Monsoon.

As noted above, tropical cyclones occasionally occur during the Northwest Monsoon period and result in short-lived, severe storm events, often with strong but variable winds. The mean wind speed recorded at the Jabiru Oil Field (1984-1990) was 4.8 ms^-1 during the Southeast Monsoon period and 4.3 ms^-1 during the Northwest Monsoon period.

Figure 5: A three-dimensional map of the Shoals showing the individual banks.

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Last updated - 30 August, 2001

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