Festive season to bring Christmas Day heatwave to Perth and Cocos Island tropical cyclone
A satellite image of the tropical low in the Indian Ocean forecast to form into Tropical Cyclone Grant. (Supplied: NASA)
In short:
A severe heatwave will grip much of Western Australia on Christmas Day, the Bureau of Meteorology says.
Perth is forecast to hit a high of 41 degrees on Christmas Day, as a tropical cyclone forms over the Indian Ocean, potentially impacting the Cocos (Keeling) Islands.
What's next?
Another tropical low could also form in waters off the Kimberley coast at the weekend.
Western Australia is bracing for an extremely hot Christmas Day as a severe heatwave grips much of the state, while a remote island off the coast prepares for an approaching tropical cyclone.
The Bureau of Meteorology (BOM) said the low — currently located over the Indian Ocean and east of the Cocos-Keeling Islands — was likely to develop into a category 1 system on Monday afternoon and be named Tropical Cyclone Grant.
It will continue to move west towards the islands and intensify into a category 2 system by Tuesday morning.
Meteorologist Jessica Lingard said the system would likely begin impacting the islands in the next 48 hours.
A track map showing the likely path of TC Grant in the Cocos (Keeling) Islands. (Supplied: Bureau of Meteorology)
"The greatest impacts are expected to be felt on Christmas Day,"Ms Lingard said.
"Depending on the path of the system, the worst impacts would be a category 2 wind strength so that could have damaging to destructive wind gusts in excess of 120 kilometres an hour.
"It could also bring with it heavy rainfall … we could be looking at falls on Christmas Day of between 50 to over 100mm of rainfall."
Ms Lingard said impacts would ease quickly from Boxing Day as the system tracked in a westerly direction.
A map showing the heatwave forecast for WA on Christmas Day. (Supplied: Bureau of Meteorology)
The islands, around 2,000km north-west of Western Australia, are home to around 900 people, mostly spread across two main settlements on West and Home Islands.
It wouldn't be the first Christmas cyclone for the remote island.
In 2014, Tropical Cyclone Kate passed north of the tiny community, bringing strong wind gusts but causing only minor damage.
The heat will be on during Christmas lunch
Meanwhile, many Western Australians will be sweating under severe heatwave conditions on Christmas Day.
All of Western Australia can expect above-average temperatures on Christmas Day. (ABC News: Kenith Png)
The driver of the heat is a west coast trough. It will continue to deepen down the west coast over the coming days, dragging a lot of the heat from the northern regions down into western and southern parts.
"There is a lot of heat in the Pilbara and Gascoyne at the moment, some areas are forecast to reach temperatures of 46 degrees," Ms Lingard said.
"So, that trough has a lot of heat to tap into and drag down the west coast."
A severe heatwave warning for parts of the Pilbara and Gascoyne has been extended into the Perth metro area, as well as the Mid-West and South West districts.
Sweltering days and sticky nights
Maximum temperatures are expected to hover around the high 30s to low 40s, while overnight minimums won't be offering much reprieve.
Perth is forecast to only drop to an overnight low of 26 degrees Celsius, which could make it our hottest Christmas morning on record.
The current record dates back to 1915 when the city recorded a warm low of 25.9C.
"It is going to be a very sticky and uncomfortable night,"Ms Lingard said.
"We're going to be hitting those really warm temperatures very early, we're already most of the way to 30 degrees overnight.
"And unfortunately not much of a sea breeze to come through during Christmas afternoon so still likely to be above 35C around sunset."
Perth sweltered through its hottest Christmas day on record four years ago. (ABC News: Andrew O'Connor)
The city is tipped to reach a scorching 41 degrees on the big day, following a very warm 40C on Christmas Eve.
Perth recorded its hottest Christmas Day ever in 2021, reaching a high of 42.8 degrees.
"One of the models we use quite regularly is forecasting 43 degrees,"Ms Lingard said.
"But hopefully we're not going to be breaking both the morning and afternoon records, that would be a very uncomfortable day."
After the oppressive heat of Christmas Day, temperatures are expected to drop. (ABC News: Kenith Png)
The last days of 2025 to be cooler
Fortunately, once that trough is finished baking the west coast on Thursday, it will move inland fairly quickly, allowing cooler conditions to move through.
However, that means areas further inland, including much of the Goldfields, Wheatbelt and Esperance districts, will have to endure very warm temperatures for a little longer.
And with those hot dry conditions also comes the increased risk of bushfires.
Ms Lingard said a fire danger warning would likely be issued for the Mid West coast on Monday, with extreme fire danger conditions creeping further south as that heat shifts lower.
There will be a risk of fire in parts of WA's Mid West. (ABC News: David Weber)
There is also a risk of thunderstorms for parts of the Mid West including the Geraldton area on Christmas Eve and Christmas Day.
"Like the storms we've seen with the last few west coast troughs, [they] are likely to be high based thunderstorms, so very little rainfall expected to reach the ground," she said.
"So there is that risk of dry lightning which exacerbates the bushfire risk during those days."
The bureau is also forecasting a potential tropical low forming off the Kimberley coast later this week.
If it forms, there is a low risk it may further develop into a tropical cyclone from Saturday.
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