A week-long heatwave is gripping NSW and some parts of the state could see December records challenged. A high pressure system over the Tasman Sea is directing a hot air mass across Australia's southern and eastern states this week. This stagnant weather pattern will remain largely unchanged until the middle of next week, resulting in severe heatwave conditions for much of NSW. Both maximum and minimum temperatures are likely be climb more than 10 degrees above average at times during the next week. In the far west, daytime temperatures could exceed 40 degrees for seven days in a row, while nights should only cool to the mid to high twenties. Tibooburra's average maximum temperature during the next week will be around 42 degrees, while minimums are forecast to range from 27 to 30 degrees. In the Riverina, Griffith is forecast to reach 44 degrees on Monday, which is 13 above average for this time of year and would match the site's December record. While many places in NSW will have experienced days and nights this hot before, the prolonged nature of this week's heatwave makes it dangerous to the health of people and animals. According to the Bureau of Meteorology, severe heatwave conditions are already affecting parts of central and northern NSW and will spread into the state's southern inland from Saturday. A low pressure trough is expected to cross the state from west to east during the middle of next week, flushing the heat out of most districts and allowing temperatures to return closer to average. This change is also likely to produce showers and thunderstorms as it moves over the state and some of these storms may become severe. Gusty winds ahead of and with the change will also elevate fire danger ratings. Be sure to keep up to date with the latest forecasts and warnings during the next week. The four steps to staying healthy during a heatwave are: Drink plenty of water Take measures to keep your body cool Take care of others, particularly the elderly and children Have a plan in case you need help