Adelaide is set to face six days of temperatures above 35 degrees Celsius in what the Bureau of Meteorology has described as an "unusual" and "extreme burst of heat". Senior climatologist Darren Ray said a six-day run of such temperatures had only been recorded three times during November and December since European settlement. Temperatures in the city are forecast to hit 35C today and Tuesday, while Wednesday is expected to reach 36C, Thursday 37C, Friday 38C and Saturday 42C ahead of a change. On Sunday temperatures are forecast to fall to 30C. Mr Ray said such temperatures were not normally seen until the "height of summer, late January and early February". "It's certainly an extreme burst of heat and that run of six days of 35C or more has only happened three times in Adelaide's entire temperature record for November and December," he said. "There was a really hot run during November in 2009 and the other two were in 1931 and 1898. "It's pretty unusual." Mr Ray said a hot weather system was starting to become established over south-east Australia, which tended to block cold fronts coming up from the south to break up the heat. "We're expecting that high pressure system to produce some northerlies through Friday and Saturday, which is going to push up the temperatures even further." He said the high pressure system was "fairly typical" of an El Nino weather phenomenon, which was "peaking at the moment". "This is looking very much like it will break down as we go through the early parts of next year," Mr Ray said. Adelaide has experienced several hot spells throughout November and December, recording its hottest December night in more than a century last week when it reached 33C before 4:00am. October was also hotter than average, shattering the city's all-time October record by more than 5C. Temperatures are expected to become "a fair bit milder" before Christmas. "My long range punt at this stage for Christmas is something around a 29 degree maximum for Adelaide," Mr Ray said. "[This week's] temperatures are not an indication of particularly extreme temperatures for the rest of summer." He said milder conditions were expected during January and February.