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  Home  > Status Report  > Chapter 2 - Physical Environment  > 2.1 Weather & Climate of Cleveland Bay

2.1.3  Average climate

Climate of the region is defined as hot, humid and tropical with a summer rainfall maximum (more than 80% of rainfall occurs between October and March) associated with the Australian summer monsoon (Suppiah, 1992; Sturman & Tapper, 1996). Climate averages for the Townsville AMO station are provided in Table 1. Note that for rainfall, which tends not to be normally distributed, the average is not a good measure of what to expect. Better measures of “average” rainfall (and river flow) are obtained from the median and percentiles of the observations (50% of observations will have values above or below the median or 50^th percentile; 90% of observations will be at or below the 90^th percentile or there is a 10% probability that values will exceed the 90^th percentile etc). The rainfall regime of Cleveland Bay is characterized by very high inter-annual variability – the driest year on record (and also for Queensland) was 1901-1902 when only 80 mm of rainfall was recorded. In the wettest year, 1939-1940, 2646 mm was recorded.

Table 2.1: Some average monthly and annual statistics for Cleveland Bay. Monthly and annual averages for Townsville AMO apart from sea surface temperature which are for 1^o latitude by longitude box closest to Cleveland Bay from historical data sets (see text).

^*Averages for relative humidity, pressure and winds are for 3pm observations. Relative humidity at 3pm is ~ 10% less than at 9am; sea-level pressure is ~ 4mb lower than at 9am; wind speeds are ~ 3m/s higher than at 9am; wind components are more easterly and southerly than at 9am.
^†U-wind is the zonal or east-west wind component, calculated as wind speed x sin (wind direction).
^‡V-wind is the meridional or north-south wind component, calculated as wind speed x cos (wind direction.)

Over the period 1969-1997 there were 18 tropical cyclones^[2] within about 100-150 km of Cleveland Bay (ie about 6 per decade or 1 every 1-2 years). Of these 18 TCs, 3 occurred in December, 6 in January, 3 in February, 5 in March and 1 in April. Five were Category 0 (average wind speeds at least 17 m/s), 9 were Category 1 (average wind speeds 17-25 m/s, central pressure 1000-985 mb), 1 was Category 2 (average wind speeds 25-33 m/s, central pressure 985-970mb) and 3 were Category 3 (average wind speeds 33-44 m/s, central pressure 970-945). Category 3 tropical cyclones were Althea in December 1971, Charlie in February 1988 and Aivu in April 1989. Over this record period no Category 4 (44-56 m/s, 945-920 mb) or Category 5 (> 56 m/s, < 920 mb) were recorded in the Cleveland Bay area (information taken from Puotinen et al., 1997).

²Defined by the Australian Bureau of Meteorology as a "non-frontal synoptic-scale cyclonic rotational low pressure system of tropical origin, in which 10 minute mean winds of at least 17.5 m/s occur, the belt of maximum winds being in the vicinity of the system's center."

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This page was last updated on Thursday 11 April 2002
by David Bailey