AFTER days of threatening to form, a mammoth tropical storm off North Queensland officially became Cyclone Sandra at 4am today, a Category 1 cyclone that is expected to gradually move east and then south.

The Bureau of Meteorology put out a Tropical Cyclone information bulletin at 4.45am, announcing the category 1 cyclone formed about 990 km northeast of Mackay at 4am, and was moving northeast at about 13 kilometres per hour.

Cyclone Sandra is expected to intensify as it moves moving east during the next 24 hours, before turning south and continuing into the middle of next week.

The Bureau of Meteorology said Cyclone Sandra doesn't pose a threat to the Australian coast at this stage but still has the potential to hit Queensland by mid to late next week.

Senior forecaster Pradeep Singh said BOM still can't confirm which way the cyclone is going to go.

"It's moving away but the problem is while the cyclone is in the vicinity, there is still a threat it could hit Australian coasts," he said.

"It still has the potential to come back to us and affect the coast. During the weekend it will take a more southerly trek which will head more towards New Caledonia."

Mr Singh said Cyclone Sandra is a "solid system" and will develop to Category 3 by the end of the weekend, with the potential to develop even further after that.

LAST NIGHT, meteorologists were still scratching their heads about the development of a mammoth tropical storm off North Queensland.

But most forecasters expected it will officially become a cyclone as early as today.

At it's 11pm update last night, the Bureau of Meteorology said the low was about 920km northeast of Mackay and moving northeast at about 12km/h.

The Bureau said it expected the storm to ''intensify and develop'' into a tropical cyclone over the next 12 to 24 hours.

The weather system, that would be named Cyclone Sandra, is expected to move southeast over the weekend.

Water catchments along the coastline are so saturated that just another 50mm of rain could cause flash flooding.

"Who needs a cyclone now?" commented Weather Channel forecaster Dick Whitaker, one of many professionals trying to chart the storm.

One thing the forecasters are sure of is that the would-be Sandra is building.

Weatherzone chief meteorologist Alex Zadnik said the system deserved close watching.

"I'm in line with the bureau's thinking on this for the next three days," he said. "It looks like it will continue intensifying. It'll drift southeast initially but it's uncertain what it will do next week.

Mr Whitaker said the storm would likely move away.

"But two models have it drifting back about Wednesday," he said. "We think that is a less likely scenario but it does raise a red flag."

The east coast might be soaked but parts of Cape York and western Queensland are despairing for rain, with the Gulf of Carpentaria just recording its driest wet season in 23 years.

National Climate Centre climatologist Karl Braganza said a severe weather situation was developing in the north and interior.

"Along the coast, especially in the southeast, it's been very wet," Dr Braganza said.

"But once you get across the (Great Dividing Range) and in the north, it's been a reasonably dry summer."

Dr Braganza said a late and patchy monsoon had reduced rainfall in the north, although it was not too late for further precipitation given the cyclone season did not end until next month.

Originally published as Sandra forms into Category 1 cyclone