Update 4pm: People from Lancelin to Albany have been told to prepare for possible thunderstorms and heavy showers.
The warning is for people in parts of south-west in a line from Lancelin to Wongan Hills to Southern Cross to Hyden to Narrogin to Albany. This includes people in, near or between: Bunbury, Perth, York, Southern Cross, Narrogin and Albany.
A deep low pressure system is expected to approach the south-west of the State during tomorrow morning, moving south of the south coast later in the day, resulting in squally conditions about the south-west in the afternoon and evening.
Winds will strengthening winds across the region during Tuesday afternoon and evening with possible squalls.
Squalls may cause winds in excess of 125km/h
A slow moving cold front is currently affecting the south-west of the State with Witchcliffe already recording 41.8mm between 8am and 9am this morning.
The Weather Bureau warns the conditions could lead to heavy rainfall and even flash flooding, making road conditions hazardous.
Those in affected areas are advised by the Department of Fire and Emergency Services to prepare for the continuing conditions.
DFES advise people to find safe shelter away from trees, power lines, storm water drains and streams if they find themselves outside.
To close your curtains and blinds, and stay inside away from windows as well as unplug electrical appliances and do not use land line telephones if there is lightning.
If there is flooding, create your own sandbags by using pillow cases filled with sand and place them around doorways to protect your home.
Do not drive into water of unknown depth and current.
Slow down and turn your headlights on.
Be alert and watch for hazards on the road such as fallen power lines and loose debris.
And if it is raining heavily and you can not see, pull over and park with your hazard lights on until the rain clears.
Anyone who suffers from significant property damage can call the State Emergency Service on 132 500.