And widespread rainfall developing along the west coast with the passage of a trough and front this weekend.

A parent low is expected to form along the cold front during Saturday over the SWLD which will become slow moving as it meanders along the south coast into early next week. That has the potential to produce severe weather with heavy rainfall leading to flash flooding and damaging southerly winds.

Thunderstorms also will be scattered in nature over the coming days, with heavy rainfall and gusty winds today, but a small hail risk developing across the weekend over inland areas in the clearer slots that may form in the rain band.

Thunderstorm Forecast - Valid Friday May 28th 2021.

90% chance of thunderstorms developing within 20km of a given point during Friday in the pink zones. The risk tapers down by 10% per colour down the radial as you move inland. Storms unlikely to be severe.

Rainfall for the coming 7 days shows heavy falls across the south coast with some places inland of Albany potentially receiving upwards of 200mm through the event. This could shift further east or west depending on the track of low pressure which is still yet to be determined. But one thing that is clearer is that the worst of the weather will be on the south coast rather than the west coast.

The track of the front through to developing into low pressure and then moving along the south coast will take the best part of 4 days, meaning the wet weather will be quite widespread for a number of days. Inland areas could see another months worth of rainfall ontop of already a wet May across the SWLD.

Rainfall percentages - Month to date 28th May 2021. Showing widespread areas of above average rainfall. The west coast should see rainfall turn above average by the end of this event and further heavy falls over the inland could see near record May rainfall be achieved.

GFS 500mb chart - Valid Friday May 28th 2021. Saturday

Front turning into an upper low over SWLD with a trough back north of the feature along the west coast bringing widespread rain and thunderstorms into the region. Some falls could exceed 50mm along the coast with thunderstorms with 30-50mm over the inland with a broad band of rain.

GFS 500mb chart - Valid Friday May 28th 2021. Sunday

Upper low deepens over southern coastal WA with heavy rainfall rotating around the feature. Showers and thunderstorms continue for the inland, though rain will ease over the central coast with a few showers to follow. Showers could be quite heavy and frequent at times around Perth and the west coast with local hail and thunder.

GFS 500mb chart - Valid Friday May 28th 2021. Monday

Upper low moves east along the south coast. The heavy rainfall and thunderstorm activity will continue along the south coast from Albany towards Esperance with the low becoming progressive later in the day and moving east. Showers continuing for the west coast with local hail. Showers and some thunder over the southern inland with some hail possible.

GFS 500mb chart - Valid Friday May 28th 2021. Tuesday

Upper low over the south coast will contract towards the SA border. Showers will continue for the south coast with some moderate falls. Some local hail and thunder possible in the far east. Clearance will develop for the west and southwest though cloudy skies with patchy rainfall will move back to the Pilbara coast with another impulse of moisture from the Indian Ocean which I will cover off over the weekend.

So this event has the potential to bring severe weather. Be aware that rainfall totals with thunderstorms over the coming days could result in flash flooding over the inland, with the water table up after recent heavy falls.

Flash flooding and damaging winds are possible along the south coast from Margaret River to Esperance this Sunday then to Tuesday and I will produce charts once the confidence is higher.

Need more weather information for your part of the world? Let me know by emailing me karllijnders@weathermatters.org

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