A low pressure trough is dragging tropical moisture down to southwest WA, delivering showers and humidity levels more like those felt in the north.

Over the last couple of days, a trough off the WA coast has been transporting tropical moisture from the northeastern Indian Ocean to the state's southwest, resulting in showers and high humidity in Perth and a large area surrounding the city.

The air is so wet that thunderstorms, a common occurrence with troughs, are having trouble forming. Although rainfall has been generally light over the region, there has been heavy falls at times, adding even more moisture to an already saturated atmosphere over the the southwest.

At 9am Saturday, the dry bulb temperature in Perth was 22.3 degrees, with heating limited by the extensive cloud cover. That wouldn't be too bad if relative humidity wasn't a sticky 96% at the time. The dew point temperature at 9am was 21.6 degrees, and the closer the two temperatures are, the wetter the air is. The humidity is making it feel around 4-5 degrees warmer than the actual temperature.

Sunday is also going to feel pretty sultry over southwestern parts of WA, but humidity levels will drop into the new working week as the dry bulb and wet bulb temperatures diverge, and a bit more sunlight to dry up the air during the day.