The office predicts next year will be 0.43 degrees to 0.71 degrees warmer globally than the average temperature between 1961 and 1990, with a ''best fit'' of 0.57 degrees warmer. If the best fit prediction holds true, that would make next year the hottest year since instrumental records began.

So far, the warmest years on record are 2010 and 2005, both of which were 0.54 degrees above the late 20th century average of about 14 degrees. They are followed by 1998, which was 0.51 degrees above the 1961-90 average as a result of a strong El Nino phase, which enhanced warming. This year is ranked as the ninth warmest year on record.

''Taking into account the range of uncertainty in the forecast and observations, it is very likely that 2013 will be one of the warmest 10 years in the record, which goes back to 1850, and it is likely to be warmer than 2012,'' the office said in a statement.

While local temperatures vary, on a global scale it has been 27 years since the world experienced a month that was colder than average.

Of more immediate concern, a cool change and possibly a sprinkle of rain will be on the menu by the time most Sydneysiders sit down to Christmas lunch this year.