The Bureau of Meteorology (BOM) says there is a moderate risk of a tropical cyclone forming near Darwin on Boxing Day, as showers and storms move in from the north.
Speaking on ABC Radio Darwin on Friday morning, BOM senior forecaster Billy Lynch said a tropical low sitting north of the Tiwi Islands was expected to move south with a monsoon trough.
"It's most likely going to be passing fairly close to the Tiwi Islands tomorrow and then drifting southwards, either over the Daly district or across the Timor Sea," he said.
"If it does take a track over the Timor Sea, there is a risk of that low developing, possibly to a tropical cyclone."
Mr Lynch forecast a low risk of a tropical cyclone developing on Christmas Day, and a moderate risk (30 to 50 per cent chance) of one developing on Boxing Day.
"It still is a finely balanced situation, highly dependent on what track it takes," he said.
Even if the tropical low moves over the Top End and doesn't develop into a cyclone, Mr Lynch said the weather system would "definitely strengthen the monsoon".
That means Territorians can expect strong winds developing around the coastline and possible heavy rain across the Top End, creating "cooler, cloudier and wetter weather".
Showers and thunderstorms would likely increase today and into the weekend as the monsoon system approaches, Mr Lynch said.
He encouraged Territorians to stay across the latest weather updates.
Currently the BOM is forecasting a maximum temperature of 31 degrees in Darwin on Christmas Day, with a predicted 95 per cent chance of rain and a chance of a thunderstorm.
In Alice Springs, the BOM predicts a 36-degree day, with a slight chance of showers.