Tuesday, 9 January 2018 - Monthly Climate Summary for Greater Sydney - Product code IDCKGC15L0

Greater Sydney in December 2017: a warm start to summer

December rainfall was average to below average in the Sydney region, with more rainy days than average for December. A heatwave in the middle of the month resulted in above average mean daytime and overnight temperatures throughout Sydney.

Average rainfall totals across the city

• Rainfall totals were average to below average in Greater Sydney during December, with more rain days than the December average
• Total rainfall for Sydney (Observatory Hill) was 47.2 mm, 61% of the long-term December average of 77.5 mm
• Rain fell on 16 days at Observatory Hill, above the December average of 12 days, but only one day received more than 10 mm, less than average of two days
• A similar pattern occurred in the west: Richmond received a total of 46.6 mm over 16 rain days, a slightly below average rainfall total, but more than the December average of ten rain days
• The heaviest falls came at the start of the month, when an extensive cloud band with embedded thunderstorms crossed the city on the 3rd; falls in excess of 10 mm were recorded throughout Greater Sydney, and showers continued for several days

First heatwave of the summer

• The mean daily maximum temperature for Sydney (Observatory Hill) was 27.8 °C, which was 2.6 °C above the long-term average of 25.2 °C and the fifth-warmest December on record
• Daytime temperatures were very much warmer than average across the city, with mean maximum temperatures for the month up to 4.0 °C above average at Penrith Lakes
• Low intensity heatwave conditions in Sydney began on the 12th and continued for several days, reaching severe status by the 18th; during the heat in the middle of the month, several sites had their highest December day on record
• A number of sites in the western suburbs had their warmest mean December days on record, and only six days failed to reach 25 °C or higher at Observatory Hill, the lowest number of days since 2005
• Overnight temperatures were also warmer than average; the mean daily minimum temperature for Sydney (Observatory Hill) was 19.9 °C, which was 2.4 °C above the long-term average of 17.5 °C and the second warmest on record behind 2016
• At 9am on the 20th, Sydney (Observatory Hill) had already reached 35.3 °C, the second-highest 9am temperature on record at the site (after 36.5 °C on 18 January 2017)
• Numerous sites around Greater Sydney exceeded their December records for the number of consecutive warm nights of 20 °C or above, including Sydney (Observatory Hill) with 11 consecutive nights (14th to 24th, previous December record was seven such nights in December 1990)
• Several sites had their highest December mean daily minimum temperature on record for the month, or their warmest December night (highest daily minimum temperature) on record on the 20th

Extremes Maps Records Summaries Daily observations Important notes the top

Extremes Maps Records Summaries Daily observations Important notes the top

* note: there are gaps in the historical record at this site, so it is possible a higher value has gone unreported

Extremes Maps Records Summaries Daily observations Important notes the top

Extremes Maps Records Summaries Daily observations Important notes the top

Extremes Maps Records Summaries Daily observations Important notes the top