For the first half of May this year, the average daytime temperature was 24.3 degrees, almost 5 degrees above the norm for the month as a whole. Swimmers enjoy the warm weather at Coogee Beach on Tuesday. Credit:Wolter Peeters The closest call was back in May 2007, when the first half was a still mild 23.9 degrees on average, Acacia Pepler, a climate expert at the bureau, said. Tuesday's forecast top of 27 degrees would be a good degree warmer than the typical maximum for any of Sydney's three formally declared summer months. The records have not been confined to Observatory Hill, but extend inland as well.

For stations with at least 20 years of records, a few have already reported record numbers of days in May with at least 25 degrees, Agata Imielska, a senior bureau climatologist, said. Still a chance for a last dip before the cold finally arrives. Credit:James Brickwood These include (with Tuesday added): Eight days at Canterbury Racecourse (the previous was six in 2014)

10 days at Bankstown Airport (the previous was seven in 1990) – 47 years of data

Eight days at Badgerys Creek (the previous was six days in 2007)

10 days in Penrith (the previous was seven in 2007)

11 days in Richmond (the previous was five in 1997) For the city itself, seven days this month have reached 25 degrees or more, including Tuesday. That makes it the equal most such days, sharing the honours with 1957, 1958, 1990 and 2014.

A list of the 10 warmest days in May - with Tuesday's 28.3 degrees just missing out. Credit:Bureau of Meteorology Record run of mild nights Nights have also been milder than normal, although the difference is less stark than during the day, largely because of the clear skies letting the mercury drop quickly after sunset. So far this month, minimum temperatures are averaging 14.3 degrees, compared with the typical 11.6 degrees for May.

With the typically cooler half of the month ahead, Sydney will struggle to top May 1989, when the record high minimum of 14 degrees was set. What's most interesting, though, is the persistent warmth. Remember what you were doing on September 29 last year? That's the last time the city recorded a night with a temperature below 12 degrees. In bad news for purveyors of woollen scarves and other cool-weather garb, the past 230 nights in Sydney have been 12 degrees or warmer. That tally easily eclipses the previous record of 217 nights, which ran to May 19, 1974, and May 8, 2004, Ms Pepler said.

And there's little sign of a let-up, Jacob Cronje, a senior meteorologist with Weatherzone, said. While there are a couple of nights in the next week when the 12-degree string might be broken, days are likely to remain above-average for the remaining two weeks of May, Mr Cronje said. "Those mild nights should stick around until June," he said. "It's just strange, we're not used to it." Records in play Daytime temperatures are forecast to range from about 22-24 degrees for the next week, although the chance of "dramatic heat" subsides as winter nears, Mr Cronje says.

Ms Pepler said records in the offing this month include the highest average maximum of 23.2 degrees, set in 2014, the fewest days below 20 and the most consecutive days above 22 degrees (one and 19, respectively, in records set in that year). An east coast low in early January - which led to the coolest January day since 1978 - means the current tally of 130 days of 20 degrees or warmer is unlikely to challenge the 180-day record tally set in the period to May 4, 1914, she said. The First World War period was notable for another record that, so far, still stands. Sydney reached 30 degrees on May 1, 1919, the city's hottest May Day, at a time when troops were returning from foreign battlefields. Widespread warmth If this year seems warm in Sydney, you'd be right.

Temperatures for the first four and a half months of the year are running 0.35 degrees warmer than in any other year, Weatherzone's Rob Sharpe said. Nationally, it will take a lot to beat the outlier May of 1958, when mean temperatures were 2.11 degrees warmer than the long-run average (set at 1961-90 by the bureau). "We look to be in that range at the moment, but of course the second half of May would normally be cooler than the first," Blair Trewin, senior bureau climatologist, said. The next in line were two recent years, 2007 (with an anomaly of 1.73 degrees) and 2014 (1.62 degrees). Other late-season records would need another burst of warmth, and there "may be possibilities" of that next week, Dr Trewan.

Sydney has had a day of 28 degrees as late as May 25, which it notched in 1994, while Melbourne has had a 26.7-degree day as late as May 21, back in 1975. Weatherzone is owned by Fairfax Media, publisher of this website.