Perth weather: Sunshine to end in soggy twist as ex-cyclone Narelle threatens late-week chaos

Perth’s golden stretch of sunshine is set to be smashed by a wet, uncertain finish — with ex-cyclone Narelle looming as a potential game-changer later in the week.

It starts picture perfect. Blue skies. Light winds. Lingering summer heat.

Monday is warm, with the temperature expected to peak at 30C.

Tuesday follows a similar script — sunshine from wall to wall, the mercury again nudging 30C before the seabreeze rolls in.

On Wednesday and Thursday, the temperatures pushes into the low 30s with more sunshine.

But it won’t last because to the north, a powerful and unpredictable system is on the move.

Bureau of Meteorology forecaster Jessica Lingard said ex-tropical cyclone Narelle was already tracking towards WA and starting to influence conditions.

“It is moving into the WA region during today, with the system forecast to travel across the northern parts of the Kimberley during today and overnight before popping out into waters west of the Kimberley tomorrow,” she said.

And that is only the beginning.

Ms Lingard warned that the system could reintensify once it moved back over open water.

“Once it starts to move into the open waters north of the Pilbara, we are going to see it strengthening back up into tropical cyclone strength,” she said.

“We could see it reaching severe tropical cyclone strength for the third time as it moves north of the Pilbara, potentially during Wednesday.”

From there, the forecast becomes far less certain — and far more worrying.

“At this stage Narelle is expected to run parallel to the Pilbara coast on Wednesday and Thursday,” Ms Lingard said.

“But there are a range of scenarios, including a more southward track off the WA coast towards the end of the week.”

Some of those scenarios bring it dangerously close to Perth.

“There is a possibility the system will directly impact Perth,” she said.

“But models are showing a huge range of outcomes … some have it off the coast near Kalbarri, others have already pushed it through to south of Esperance.”

The uncertainty of what the system will do is so massive that the bureau has drawn a huge circle across northern WA on its seven day tropical cyclone forecast map.

“That large spread isn’t the size of the system — it’s a circle showing all the possible model outcomes,” Ms Lingard said.

“When we get five to seven days out, we really start to test the limits of tropical cyclone forecasting accuracy. They are fickle beasts.”

Despite that, Perth is certain to get rain by the weekend.

“There is a wet forecast for the end of the week and the weekend,” Ms Lingard said.

“How wet and how windy it becomes will depend on the path, movement and strength of the system.”

And that’s when Perth’s week flips.

By Friday, cloud builds, temperatures ease into the mid-20s and the first showers are likely, with up to 20mm falling.

Saturday brings cooler, breezy conditions with up to 40mm of rain predicted.,

Sunday will be even cooler and possibly wetter, with the mercury topping out at 23C.

Up north, it is already turning nasty with a flood watch issued for the Kimberley.

Ms Lingard said the Kimberley was in the firing line, with heavy rain and deteriorating conditions expected as the system Narelle crossed from the Northern Territory and into the WA coast.

“We’re looking at 60 to 120mm for Kalumburu today, with isolated falls closer to 200mm,” she said.

“These tropical lows can absolutely pack a rainy punch.”

Conditions are expected to worsen throughout Monday before easing overnight, with Broome also set to feel the effects.

“Broome will likely see rainfall tomorrow and again on Wednesday, with totals depending on how the system tracks,” Ms Lingard said.

However, where Narelle then goes remains anyone’s guess.

“Some scenarios bring it down across the coast and into the south west, others keep it offshore,” Ms Lingard said.

“It’s very much a watch-and-wait situation but people in western and southern WA should be keeping a close eye on it.”

PERTH WEATHER FORECAST

• Monday: Partly cloudy, Max 30 ⛅️
• Tuesday: Sunny, 15-30 ☀️
• Wednesday: Sunny, 16-31 ☀️
• Thursday: Sunny, 18-31 ☀️
• Friday: Showers, 21-27 ☔️
• Saturday: Showers. Becoming windy, 18-25 ☔️
• Sunday: Windy. Showers, 17-23 💨

Forecast sourced from the Bureau of Meteorology.