The “train effect” struck Western Australia, bringing the heaviest August downpour in 48 years
Image credit: JMA/Himawari-9, RAMMB/CIRA, The Watchers. Acquired at 02:10 UTC on August 7, 2024
Multiple rain records were broken in several parts of Western Australia on Wednesday, August 7, 2024. The town of Pearce recorded 45.6 mm (1.80 inches) of rain — the highest August rainfall in 48 years.
The heaviest August rain in 48 years was recorded in Pearce, a town north of Perth on Wednesday morning as an unstable airmass moved across the region. Severe thunderstorms were triggered by a coastal trough extending from offshore Two Rocks to Bullsbrook.
Radar imagery showed heavy rain and thunderstorms continuously moving from the Indian Ocean into districts north of Perth, a phenomenon known as the “train effect.” This effect occurs when thunderstorms or showers repeatedly impact the same location, causing significant rainfall.
The train effect led to flash flooding in the northern suburbs of Perth early Wednesday morning. Pearce, located north of Perth, experienced a heavy rain rate with 32 mm (1.26 inches) of rain falling in the hour to 06:15 local time (LT) and 10 mm (0.39 inches) in just 10 minutes to 05:50 (LT).
This 10-minute rainfall rate had an annual exceedance probability (AEP) of 20%, meaning it has a 20% chance of occurring in any given year.
Significant rainfall totals were recorded in the 24 hours to 09:00, breaking multiple rain records on August 7:
- Pearce: 45.6 mm (1.80 inches), marking the heaviest rainfall in 48 years, with most rain falling after midnight.
- York: 24 mm (0.94 inches), the heaviest daily August rainfall in 26 years.
- Jandakot: 48.8 mm (1.92 inches), the heaviest August rain in seven years.
- Garden Island: 41.8 mm (1.65 inches), the heaviest August rain in seven years.
- Perth Airport: 33.4 mm (1.31 inches) in 12 hours, the heaviest August rain in four years.
How much rain did you get?
— Madre Swift Justice (@JayStill4) August 6, 2024
Jandakot – 48.8mm
Bickley – 45.6mm
Pearce – 45.6mm
Garden Island – 41.4mm
Perth Airport – 33.4mm
And of course Murray in Mandurah has cracked the shits because he only got 7.8mm.
Perth Weather Live pic.twitter.com/buqD8Wmg8C
The heavy rain had eased in the region as of 10:00 on Wednesday, with some rain extending from the Great Southern to the southeast coastal district. The rain is expected to clear Western Australia by Wenesday evening, with a high-pressure system moving in as the front moves away into South Australia.
Another cold front is forecast to sweep across southwestern Australia late on August 11 into August 12, potentially bringing more heavy rainfall and thunderstorms to the region.
References:
1 Heaviest August downpour in 48 years for WA town – WeatherZone -August 7, 2024
Rishav Kothari is Editor-in-Chief of The Watchers, where he runs the newsroom and covers earthquakes, volcanoes, severe weather and space weather.
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