After some suburbs saw light showers to kick off the working week, all will be baking in summer-like heat by Friday. Many suburbs across Sydney started today with a light shower in the morning, with sunnier skies appearing before lunch. Onshore winds are keeping a lid on the top temps, sitting comfortably in the low 20's. From Tuesday until Friday, temperatures will be on the up. A hot air mass moving ahead of a low pressure trough will begin to edge into the state. On Wednesday, we will have sunny skies throughout the basin, with western suburbs beginning to nudge the mid-30's and low-30's for the coast. Thursday will see the mercury move into the high-30's for outer Sydney suburbs. The city and eastern suburbs will escape a majority of the heat under breezy onshore winds, although it will be more humid. Overnight into Friday, it will be a stuffy night, only cooling to around 20 degrees. Friday looks to be hottest day in the run with high 30's likely in all suburbs. There is potential for some places, particularly in western suburbs, to see their first 40-degree day since last year. A gusty cool change will arrive late on Friday or early Saturday morning - bringing some relief.