Tuesday, 2nd November

MONTHLY CLIMATE SUMMARY - NSW REGIONAL OFFICE

NSW October 2004: Extremes in rainfall, temperature, hail and wind.

Overview: October in NSW was a month of extreme weather events. The beginning of the month saw an intense low-pressure cell bring strong winds, heavy rain and cold temperatures to various locations in NSW. Then, a spell of very hot weather from the 12th to the 14th saw a number of centres across the state (including Sydney, Wollongong and Gosford) record their highest October maximum or minimum temperatures on record. Less than a week later, on the 17th and 18th, maximum temperatures once again struggled to reach only the mid teens across large parts of eastern NSW as a trough of low pressure combined with an onshore easterly airflow brought widespread cloud and rainfall. This marked the beginning of a significant wet spell (along the coast and ranges) between the 17th and 23rd that caused flash flooding and river flooding in parts of the coastal districts. Falls of between 300 mm and 400 mm were recorded at some locations in just 4 days. Following this episode, another low-pressure cell on the 24th triggered widespread severe thunderstorms in central and eastern districts with giant hailstones (estimated up to 12 centimetres in diameter) that caused major damage in the Hunter district. One more very intense low-pressure cell, off the far south coast on the 27th, resulted in severe winds across southeast districts and widespread damage in the Sydney, Wollongong and Blue Mountains regions. A maximum wind gust of 124 km/h was recorded at Green Cape on the South Coast.

October 2004 Rainfall: Below average October rainfall affected southern and northern border districts west of the tablelands. Along the southern border, monthly totals in many locations ranked amongst the lowest 10% of records for October with some places recording lowest ever October rainfall such as Albury. Significant rainfall across parts of western NSW on the 1st resulted in some average to above average monthly totals west of the divide, however this event had little or no impact to the north and south. In contrast, much of eastern NSW east of the divide recorded above average October rainfall. The low pressure events at the beginning and in the second half of the month contributed most of the rain with many locations recording monthly falls ranked in the highest 10% of records for October. Some places near the coast received highest on record rainfall totals for the month with falls in excess of 400 mm.  See Map 1.

August 2004 to October 2004 Rainfall:  While the wet October weather in the east generally swung the trend in 3-month rainfall towards above average falls in the east, persistent dry conditions in the west caused the areas of below average 3-month rainfall to expand across southern and northern inland areas. See Map 2.

October 2004 Temperatures: In general, mean monthly maximum temperatures across NSW were above the long-term average for October. In some northern and western districts they were considerably higher than normal, with locations in the southwest of the state recording mean monthly maximum temperatures 3 to 4 degrees above average for October . See Map 3. Mean monthly minimum temperatures were generally within 1 or 2 degrees of normal for October and varied from above average to below average across the state. See Map 4.

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/