Sydney-siders will be flocking to the beaches and cranking up their air conditioners with a brief burst of heat for the end of the working week. A low pressure trough sweeping across southern Australia is drawing a hot airmass into eastern NSW today, causing temperatures to climb. On Thursday western parts of Sydney are expected to reach the high 30s, with 38 degrees in Penrith and Richmond. For Penrith this would make it the eighth day this month it has exceeded 35 degrees. For the city and suburbs in the east the mercury should max out in the high 20s or low 30s due to a cooling sea breeze. Friday is going to be the hottest day as winds tend northwesterly and the hot airmass peaks. On this day, the westerlies may hold out the sea breeze, allowing the city to warm to the high 30s, while the west hits the low 40s. The extreme heat and dry northwesterly winds will also exacerbate the fire danger across New South Wales, including in Sydney, so residents should keep an eye on the weather and any fire weather warnings. Cloud will build later on Friday ahead of the trough, which is expected to arrive between 8pm and 11pm causing winds to tend southerly. These southerly winds will be strong and gusty, bringing a drop in temperatures and relief to hot and bothered locals. The trough also brings a risk of showers and thunderstorms, most likely during Friday afternoon and evening. Cooler, mostly cloudy days and showers are expected over the weekend, with maximum temperatures in the mid 20s across the Sydney Basin.