In its first official advice on the developing cyclone, just released, the Bureau of Meteorology said a tropical low had intensified overnight, northeast of the Wessel Islands off the NT coast.

Sustained winds near the centre of the tropical low are 45kmh with wind gusts to 85kmh.

The low is located 195km north northeast of Nhulunbuy and 410km east northeast of Maningrida.

It is moving east at 9kmh before it is expected to reverse its track tonight.

It is expected to slowly track towards the NT coast during the next three days.

There's a high chance the low will intensify to Tropical Cyclone strength in the early hours of Thursday morning.

The bureau is expecting the system to intensify to Category 2 strength on Thursday, and cross the coast between Maningrida and Goulburn Island early on Friday.

Gale force winds may start impacting parts of the northern coast from Wednesday.

A marine wind warning for strong winds has now been issued for the Arafura Coast.

Rainfall amounts will be highly dependent on how far south the system tracks through the Top End.

The north coast is likely to experience the highest rainfall with 3 day totals of 200-300mm, with isolated falls up to 500mm in the hardest hit places.

Daily rainfall totals could exceed 200m in locations close to the system.

The flood team will be assessing the possible impacts of rainfall for the Top End, and a Flood Watch may be issued later this week.

"The low is expected to turn to the west-southwest overnight tonight," the bureau says.

"It will continue to intensify and is likely to develop into a tropical cyclone on Wednesday night. The system will approach the north coast later in the week.

"Gales, with gusts over 90kmh, may develop about coastal and adjacent inland areas between Cape Shield and Cape Don on Wednesday night and extend westward on Thursday morning.

"Heavy rainfall is expected to increase about the north coast from Wednesday.

"Abnormally high tides are expected about the north coast during the next few days as the system approaches."

Top End residents have been warned to prepare for a cyclone and activate their household plan.

On its expected course, the cyclone - which may then be downgraded to a tropical low - would impact Darwin on Friday.

Further advice on cyclone emergencies is available at www.securent.nt.gov.au

A second cyclone called Blake has already formed off the WA coast and has reached category one to drop large amounts of rain in the Broome region.

Like much of the rest of Australia, the Territory is experiencing one of the driest periods in its recent history with a succession of failed wet seasons.