The ACT has set a new record for the warmest winter reaching a new average temperature of 14.1 degrees.

The city recorded a very wet June with 250 per cent of the normal rainfall during the month, while July 2013 was Canberra's warmest July on record.

Some frosty overnight temperatures in mid to late August failed to drop the overall temperature for the three months of winter.

The weather bureau's Sean Carson says the capital has seen some unprecedented heat for this time of year.

"July was what was really impressive in terms of heat, " Mr Carson said.

"Then August got back to some pretty cool conditions, in fact we had our coldest week of weather in winter in the third week of August.

"But just when we started to rug up our clothes again, and the snow really started to fall in the Alps, it has really warmed up in this last week in August and we actually saw some unprecedented heat.

"And that has bumped up that winter average temperature again. "

Mr Carson says the latest figures also indicate a long-term trend of warmer winters.

"The record we are breaking here for the warmest winter was actually previously set only two years ago," he said.

"So we are now seeing two of our warmest winters occurring in the last three years, so that's quite a trend."