A small but intense low pressure system will cause a burst of wind, rain and unseasonably cool weather in the southwest of WA on Wednesday.

The low is expected to develop near the Lower West or South West coasts of WA on Tuesday night and strengthen on Wednesday morning. The deepening low pressure system will cause wind, rain and surf to increase rapidly on Wednesday, while dropping temperatures to levels more typical of late spring than the middle of summer.

Most models predict the low to be located somewhere near the southwest Capes on Wednesday morning, before moving towards the southeast, possibly passing near or over the state's South West District on Wednesday.

Image: Predicted position of an intense low pressure system off southwest coast of WA on Wednesday, according to the ECMWF-HRES model.

Strong winds and potentially damaging gusts are possible along parts of the South West and Lower West coasts during Wednesday. This may include Perth if the low is located far enough to the north.

The heaviest rain should occur over the South West district, particularly near the coast, where some areas could receive more than 20mm. Rainfall totals from this system are likely to drop off fairly quickly as you move further inland or too far away from the centre of the low.

The combination of cloud, rain and southwesterly winds will also bring unseasonably cool weather to the southwest of WA on Wednesday. Perth's forecast top of 22 degrees on is nearly 10 degrees below average for this time of year.

The low should move to the south of WA from Wednesday afternoon, allowing conditions to ease in its wake. After another day in the low twenties on Thursday, warmer weather will return to Perth by the weekend.