Mangga weakens prior to reaching western Australian coast

By Courtney Spamer, AccuWeather meteorologist

Updated May. 23, 2020 5:28 AM

Although the tropical season for Australia officially concluded on April 30, a late-season cyclone has formed off the country's western coast.

Southwest of the island of Sumatra in Indonesia, a tropical low churned over the warm waters of the South Indian Ocean, becoming Tropical Cyclone Mangga late Thursday night, local time.

AccuWeather forecasters expect the system to drift closer to Australia in the coming days.

The above satellite image shows Mangga gathering strength on Thursday afternoon, local time, just hours before becoming a tropical cyclone. (Image/CIRA RAMMB)

"Mangga is expected to drift southward then southeastward over the next few days, into an area of warm water and light winds," explained AccuWeather Senior Meteorologist Rob Miller.

As it does so, it will continue to pass over the Cocos (Keeling) Islands with gale-force winds and rounds of heavy rain. As of Friday evening, the highest wind speed reported at the Cocos Islands airport was 61 km/h (38 mph) with the strongest winds remaining off to the south of the area.

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The Cocos (Keeling) Islands will continue to see squally showers and thunderstorms in addition to rough seas and rip currents into Saturday morning before the system pulls away.

By early Saturday morning local time, Mangga had weakened to post-tropical status.

“Although Mangga has become post-tropical, it will merge with an upper level trough Saturday night, local time as it approaches the western coast of Australia," AccuWeather Meteorologist Brett Rosio said. "Conditions will gradually deteriorate across much of Western Australia through Sunday with a heavy, windswept rain. Localized flooding will be possible in some areas. In addition to the heavy rain and gusty winds, seas will be very rough and can be dangerous for mariners.”

"The greatest impacts to Western Australia are likely to take place on Sunday, as heavy, tropical downpours stretch across the area," Miller said.

Rain and thunderstorms are anticipated to spread eastward throughout the day, eventually losing some of it's potency on Sunday night. Showers may linger in a few locations on Monday.

Rainfall amounts of 25-75mm (1 to 3 inches) are possible from cities like Broome and Port Hedland in northwestern parts of the area, through Perth and Albany on the southern coast.

An AccuWeather Local StormMax™ of 125mm (5 inches) is possible in any areas that are hit by repeated heavy downpours, most likely from Shark Bay to Port Hedland and from Perth on to the south coast.

Motorists should remember the dangers of driving through flooded roadways and avoid doing so. Residents in these areas should have an emergency plan in place should rising flood waters require them to evacuate.

Preparations may take longer, or look different, in this day and age, given the COVID-19 pandemic affecting the globe. Overall, Australia's total coronavirus case count has swelled to over 7,000 since the pandemic began.

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The tropical season for the waters surrounding Australia officially begins on Nov. 1 and continues through April 30; however, it is not uncommon for tropical activity to occur through May.

Already this May, a tropical depression formed and lingered off the coast of the Indonesian island of Sumatra.

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