Preparations are underway far off Western Australia’s north-west coast for the impact of a category one cyclone as Perth and much of the state continues to swelter in heatwave conditions.

Tropical Cyclone Grant formed on Tuesday morning in the Indian Ocean, east of the Cocos (Keeling) Islands, and could cause large waves, flash flooding and wind gusts of up to 100 kilometres per hour.

The system is moving in a west-north-westerly direction at around 8 kilometres per hour, and is expected to pass close to the Islands late on Christmas Eve or early Christmas Day.

A track map showing how a cyclone will impact the Cocos Islands later today or early Christmas Day

A track map shows Cyclone Grant will impact the Cocos Islands late on Christmas Eve or early Christmas Day.  (Supplied: Bureau of Meteorology)

The Bureau of Meteorology (BOM) has warned the cyclone could strengthen to a category two by this evening.

BOM duty forecaster Helen Reid warned residents of the islands, which is home to around 600 people, to prepare for strong winds and flooding, with the system set to make its presence felt from today.

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“We are expecting it to travel to the north of the Island rather than right across the island, but given it’s just such a small spot in the size of a large ocean, it will be very close to the island there,” she said.

“We do need to be aware of those winds getting up to around 40 knots over the night tonight, and also those seas and swells getting up to around two to four metres.

“There will be plenty of rainfall, lots of flash flooding as well and the chance of a thunderstorm, and we are expecting that westward track to continue into tomorrow and away from the Island during the course of Christmas Day itself.”

The BOM said while there was no immediate danger, residents should be prepared and keep up to date with advice.

Thunderstorms now a possibility for Perth

A low pressure trough is not only bringing hot conditions with it, but is likely to generate dry and gusty thunderstorms for areas along the west coast.

The weather bureau has updated the Christmas Day forecast for Perth, with thunderstorms now a possibility in the afternoon and early evening.

A group of people wearing raincoats and holding umbrellas while walking through the Perth CBD.

The weather bureau is now forecasting the potential for thunderstorms in Perth in the afternoon and early evening. (ABC News: Jack Stevenson)

Duty forecaster Daniel Hayes told ABC Radio Perth there could be odd storm around the metro as the trough begins to move inland.

“We’ll see some cooler temperatures around the west coast into boxing day, [but] it will still be hot further to the east, so through the Goldfields, the eastern parts of the South West land division and across the Eucla coast area,” he said.

“That heat will largely exit the southern parts of the state as we head into the weekend.

“We then have a couple of cooler days at least before we start to see the heat build again sometime next week with the next west coast trough developing.”

Perth facing 40C

A three-day heatwave warning is in place for much of the WA coastal and north interior regions between December 23 and Boxing Day.

Perth is set to reach 40 degrees Celsius on Christmas Day, and overnight temperatures around the state will be in the mid to high-20s.

A man and two women use a beach shower at Cottesloe Beach on a sunny, hot day.

Crowds of people have already been cooling off at the beach in Perth this week. (ABC News: Courtney Withers)

Day-time temperatures will be up to 15 degrees above average in the far south-west, and about 10 degrees warmer than usual for places like the metro area.

If the overnight temperature in Perth stays above 26 degrees, it could break a century-old Christmas record for the city.

Perth’s warmest Christmas morning on record dates back to 1915, when the minimum only dropped to 25.9 degrees.

The hot temperatures combined with strong winds mean high and extreme fire danger ratings blanket much of WA on Christmas Eve and Christmas Day.

Total fire bans are in place on Christmas Eve from Perth’s Swan Valley region all the way up to Kalbarri in the Midwest.

WA Emergency InformationCheck the warning information and incident map on the official EmergencyWA website.For emergency assistance during severe weather and floods, contact the SES on 131 500.If your life is in danger call triple-zero (000).Check if roads are closed on the Main Roads WA website.Report any power outages to Western Power or Horizon Power.For all local warnings and information visit ABC Emergency and listen to ABC Local Radio on the ABC Listen app.

Department of Fire and Emergency Services deputy commissioner Craig Waters urged people to be aware of the conditions.

“It only takes one person to do the wrong thing,” he told ABC Radio Perth.

“We’re asking all of the community to make sure that they follow the total fire ban rules, if one is issued for their area.

A graphic of the synoptic chart for Australia on Christmas Day.

A graphic of the synoptic chart for Australia on Christmas Day. (ABC News)

“So that includes no hot works, no four-wheel driving off-road, and no solid fuel barbecues.

“If we reflect back to the Roleystone bushfire, which was started via angle grinder, it just takes one spark to make a major bushfire event.”

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