Friday, 8th October 2004

MONTHLY CLIMATE SUMMARY - NSW REGIONAL OFFICE

NSW September 2004: Variable rainfall, hailstorms in the east.

September 2004 Rainfall: While most of NSW recorded near average total monthly rainfall, significant departures include some patches in the west that were very much below average and, in contrast, parts of the northern inland that were wetter than average for the month. Parts of southeast NSW also saw a return to significantly above average monthly rainfall for the first time since January 2004. However the far northeast corner of the state remained relatively dry, recording below average monthly rainfall for the sixth consecutive month this year. See Map 1. Some of the more significant rain and thunderstorm events during the month include:

• 3rd - 6th; a sequence of low pressure systems near southeast NSW produced 83 mm rainfall at Eden [South Coast] over 3 days. Widespread thunderstorm activity also occurred over eastern NSW and many locations were carpeted with hail on the 4th or 5th in the Illawarra and Metropolitan districts.
• 7th - 9th; a deep low and frontal system triggered significant falls in many NSW districts. Inland locations near the QLD border recorded up to 80 mm or more over 3 days, contributing to some very much above average total monthly rainfalls.
• 19th - 20th; a trough of low pressure formed off the coast and a front approached from the west resulting in widespread thunderstorms across eastern NSW. Hailstorms affected many locations in the Lower Hunter, Metropolitan, Blue Mountains and lower parts of the Mid North Coast. Large hailstones (up to 5.5cm in diameter) fell in some places and drifts of hail several centimetres deep collected in others. Heavy rain also fell on parts of the South Coast and Illawarra early on during this event (see table of Extremes).

July 2004 to September 2004 Rainfall: Above average September falls in some parts reduced the previously extensive area of below average 3-month rainfall across eastern NSW. However, continuing low falls in the northeast resulted in very much below average rainfall persisting in the northeast corner of the state for the July to September quarter, and low September falls in parts of western NSW caused an increase to the area of western districts with below average rainfall for the same 3-month period. See Map 2.

September 2004 Temperatures: Most of NSW, apart from areas in the southern inland, recorded mean monthly maximum temperatures above the long term September average. Much of the east, and pockets in the west, were between 1 to 2 degrees above average. See Map 3. Mean monthly minimum temperatures were mostly within 1 degree of the September long term average. A notable exception was a large area in the northern inland where mean monthly minimum temperatures were 1 to 2 degrees below average. See Map 4. At the end of the month a trough of low pressure drawing warm air southwards from northern inland Australia resulted in (individual station) record September temperatures at a number of locations - e.g. on the 28th, highest daily September maximums were recorded for some Upper Western stations, while on the following morning (29th) highest September daily minimums were recorded for several locations, spread mainly across inland NSW.

A note about deciles: Deciles are used to give an element (in this case rainfall) 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.

Further information:
A directory of Bureau services is available on poll fax: 1800 630 100
For the latest rainfall and temperature maps, see: http://www.bom.gov.au/climate/austmaps/