While eastern Australia has being battered by multiple thunderstorm outbreaks and historic, flooding rain, Western Australia has been seeing some warm days creep in as summer approaches. Another warm day is forecast for the southwestern corner of the country on Wednesday as the WA heat trough starts to make its presence more regularly felt. 

The WA heat trough is a regular feature on synoptic maps during the Australian summer, wrapping around the coast from the Kimberley to the Gascoyne, and sometimes further south. When the trough is active, hot air is dragged down towards the west and southwest coast from the interior, leading to temperatures regularly exceeding 40C degrees across the Central West and Goldfields, and into the mid-to-high 30s closer to the southwest coast, including Perth. 

Image: forecast 850hPa temperatures & wind for Wed 19th October 2pm AWST using ECMWF Fri 12Z run 

Right now, the heat trough is active in WA, dragging warm air from the interior, but as the trough is positioned further inland, the heat isn’t making it all the way to the coast. However, parts of the goldfields, such as Kalgoorlie, are seeing temperatures rise through the weekend. A maximum temperature of 30 degrees is forecast for Kalgoorlie this afternoon, warming further to 34 degrees tomorrow. If it reaches the mark, that will be Kalgoorlie’s warmest day since late March 

At the time of writing, the forecast maximum temperature for Perth on Wednesday is 31 degrees, 8 degrees above the long-term October average which, if achieved, would be the warmest day since early April. It’s not too unusual for Perth to experience 30-degree days in October, with the city having surpassed the mark in all but one year since 2005. 

The heat should be short lived, as a trough, then cold front look likely to cross through the southwest near the end of the week, bringing showers and colder southwesterly winds, cooling southwestern WA back towards average. Even though it will pass quickly, the warm Wednesday for Perth is a good sign that summer is on its way.