Searing, dry heat in Adelaide sent the mercury to 43.2 degrees just after three o'clock this afternoon, making it the hottest day in five years for the city. It was even hotter further north and west, where Roseworthy and Snowtown reached 44 and Port Augusta and Kyancutta got to 45. All indications are for it to be just as hot until the weekend when a weak cooler change arrives. If Adelaide reaches 40 degrees on Wednesday, Thursday and Friday it will equal the longest such hot spell in 101 years. In January 2006 there were also four consecutive days of 40 or hotter. On Wednesday a weak trough will allow sea breezes to affect coastal locations in South Australia taking the edge off the extreme heat. Humidity will also rise a little and this will help a few thundery showers develop on the Mount Lofty Ranges and parts of Eyre Peninsula. It will dry out again from Thursday as hot air lingering over the inland gets drawn to the coasts in northerly winds. The cooler change on the weekend may be so weak that Adelaide could stay above 35 degrees and close to 40 each day through to next week.