Sydney is about to be smacked with another heatwave, almost two weeks after the city was recorded as the hottest place on earth. The Bureau of Meteorology is warning of a severe heatwave to hit today and last until Monday, with Penrith expecting five days of over 40C temperatures. The Bureau are warning people in much of NSW and the ACT to "keep cool, stay hydrated and look out for vulnerable community members." The scorching temperatures are being brought on by a "really large hot air mass" which has been building for quite some time. The heatwave has affected South Australia, Victoria and now is moving into NSW. "It's a large system and it has some persistence to it. There is no big cool changes coming through either. "The temperatures will drop on Tuesday but will still be quite warm. "The city will escape most of the heat as it will be under a sea breeze, but will still get up into the 30s most days. "But the western suburbs will easily reach 40C most days and this will continue to Monday. "We are going to see quite a few really hot days that will be a struggle for anyone who doesn't live near the coast. Monday will be the worst with 35C forecast for the city, and 43C expected for the west. This comes after earlier this month, Sydney was recorded as the hottest place on earth. On January 6, the city experienced its hottest day in five years to hit a maximum temperature of 43.4C at Observatory Hill.