3 October 2006

MONTHLY AND SEASONAL CLIMATE SUMMARY - NSW REGIONAL OFFICE

NSW September 2006: Warm days, dry west of the divide

September 2006

Main points:

• 4th warmest September on record for statewide average maximum temperatures
• 5th warmest September on record for statewide average mean temperatures
• Coastal NSW recorded average and above average rainfall
• Central/southern slopes of the Great Divide, southern border and northwest areas of the state received below to very much below average rainfall
  

September 2006

Temperatures:
Well above average temperatures were recorded throughout NSW, making it the 12th consecutive September with above average mean temperatures. The statewide average mean temperature (the average of the daily maximum and minimum temperature) was 15.5ºC, which was 1.7 degrees above the historical average¹ of 13.8ºC, and the 5th warmest September on record (statewide averages calculated 1950-2006) (See Map 1). The previous warmest September was in 2001 (an average mean temperature of 15.7ºC).

The statewide average maximum day-time temperature was 2.75ºC above the historical average of 20.6ºC, making this the 4th warmest September on record. The previous highest average maximum temperature was recorded in 2000 (23.6ºC). Nearly all of NSW experienced above average maximum temperatures, with the exception of the northeast corner (See Map 2). Large areas in the southern inland parts recorded the highest maximum temperature on record. This distribution of above average temperatures were due to warmer easterly wind anomalies across the state during much of September. In addition, unseasonally warm conditions were experienced as a result of a series of intense low-pressure systems near Tasmania combined with high pressure systems in the Tasman sea, directing persistent warm to hot and dry N-NW winds over much of the state.

Nights were also mild, with a statewide average minimum temperature of 7.7ºC, which is 0.6ºC above the historical average of 7.1ºC. Below average minimum temperatures were recorded across parts of the Riverina, however, the remainder of the state experience average or above average minimum temperatures (See Map 3).

Rainfall:
September rainfall was varied throughout the state. The central and southern slopes west of the Great Divide, the northwestern and the inland southern border regions recorded below average September rainfall. Additionally, there were areas in the northwest of the state, South West Slopes and parts of the Central Tablelands and Central Slopes that recorded very much below average rainfall. Some localised pockets in those regions also recorded the lowest September rainfall on record. This distribution of below average rainfall is a result of easterly wind anomalies across much of the state and a lack of rain bearing systems from the west. Although these conditions were not favourable for rainfall in inland districts of NSW, they were responsible for parts of the coast (north of about Kiama) receiving above average and very much above average rainfall totals for September (See Map 4). In particular, an intense low pressure system that developed off the central NSW coast resulted in significant falls along the coast and adjacent ranges north from the Illawarra from around the 6th to the 13th. The statewide average rainfall for September 2006 of 26.0mm was below the average of 36.1mm and the driest since 2003 (statewide average of 11.7mm).

This statement has been prepared based on information available at 1 PM on 3 October 2006. Although every effort has been made to check them, it is possible that results may change as new information becomes available.

A note about deciles: Deciles are used to give an element (in this case rainfall or temperature) a ranking. Deciles are calculated by arranging the totals in ascending order (from lowest to highest) then splitting them into 10 equal groups (thus the groups are called deciles). The first group would be in decile range one, the second group in decile range two, etc up to the highest annual totals (highest 10 per cent) being in decile range 10.

¹Averages: Averages are based on the period 1961 to 1990 which is a convention of the World Meteorological Organisation.

Further information: Contact Louise Tilley 9296 1555, email: reqnsw@bom.gov.au

A directory of Bureau services is available on poll fax: 1800 630 100

The latest rainfall and temperature maps are available here
Climate averages for New South Wales localities are available here
Daily Weather Observations for selected New South Wales localities are available here