Perth is forecast to have its warmest day since May on Friday. A high pressure system passing to the south of WA tomorrow will direct warm inland air towards the west coast. Perth's forecast top of 27 degrees would be seven above average for this time of year and the warmest day in four months. Temperatures will be higher inland and some places in the Central West and Central Wheatbelt districts could see their warmest day since April tomorrow, including Southern Cross (30C) and Mullewa (33C). Unfortunately for those hoping for a warm weekend in Perth, milder weather will return by Saturday. A low pressure trough moving inland on the weekend will draw cooler air from the Indian Ocean over the state's southwest. Perth is expected to see near-average tops in the low twenties on both Saturday and Sunday. By contrast, a pool of hot air trapped over the state's interior will push temperatures into the mid-thirties. Saturday is tipped to be Kalgoorlie's (33C) warmest day since March.