Showers and thunderstorms developing on Western Australia's west coast will spread across much of the state, bringing some rain, which will herald a cooler change. The west of the state has been quite dry and warm lately with the aid of a stable high pressure system sending easterly winds over the region. The stable high is losing ground to an unstable low pressure trough moving in from the west. The trough is drawing plenty of moisture from the tropics, increasing humidity and fuelling the development of showers and storms. The showers and storms will be welcome in some areas, which have been very dry lately. Some of the west are now seeing their biggest rain in a month or more. Geraldton only picked up two millimetres this morning but up until now the Central West town had not recorded any rain since mid January. Just offshore, North Island has had its heaviest rain since winter, picking up a useful 12mm. Perth, which has come off four consecutive 30-degree days is about to get some welcome rain and much cooler weather. The Perth area is likely to see its heaviest rain in about two months with potential for 10-to-20mm in showers and storms. The storms will develop in the area on Sunday afternoon and will move east of the area on Monday afternoon. It is not all good news. Any thunderstorms have potential to be severe, threatening to produce flash flooding, damaging winds and large hail. A cooler, gusty southerly wind change will follow the showers and storms, dropping temperatures by about 10 degrees. Perth is forecast to stay cooler than about 22 degrees on Tuesday, which would make it the city's coolest day since spring. Last summer for much of the state's west was hotter and drier than average. Perth had its hottest summer on record and driest summer in three years.