Donna has formed outside the cyclone season which ended on Sunday, April 30.
Donna has intensified to a Category 2 tropical cyclone on the Fijian Meteorological Service cyclone scale, with maximum sustained wind speeds of 72 miles per hour (117 km/hr), equivalent to a strong tropical storm on the Saffir-Simpson Hurricane Wind Scale (SSHWS), according to the Fijian Meteorological Service.
Update: 7:27PM CURRENT bad weather, the effects of Tropical depression TD21F is expected to develop into a tropical cyclone within the next two days but its more damaging effects will not pose a threat to Fiji.
The Joint Typhoon Warning Center said the system had steadily intensified.
It was tracking west southwest. Thereafter, the system is forecast to track southeast and gradually weaken due to increased vertical wind shear.
"Vanuatu seems to have drawn the short straw in recent years in regards to cyclones, they've had way more than their fair share and this will be just another pause for them in the attempt to recover", he said.
Nasa said the imagery showed strong thunderstorms around the centre of the cyclone extending to the north in a thick band. At its peak, Donna will be equivalent to a Category 4 hurricane in the Atlantic and eastern Pacific basins.
8pm update: Earlier this evening, TD21F became Ccategory 1 Tropical Cyclone Donna (994HPA).
"The slow-moving nature of Donna will still bring the possibility of heavy rain and flooding across Vanuatu from Friday into early next week", AccuWeather Senior Meteorologist Jason Nicholls said.
The cyclone was expected to move slowly westwards on Thursday towards the northern island group of Vanuatu.
A Severe Weather Warning Bulletin for Northern and Central Vanuatu group issued by the Vanuatu Meteorology and Geo-Hazards Department, Port Vila at 5 a.m. local time, Tuesday, May 2, 2017.
Damaging gale force winds gusting up to 165km/h are expected to affect the provinces of Torba, Penama and Sanma in the next 24 hours.