Tropical Cyclone Herold has developed close to Madagascar and is expected to strengthen further in the coming days as it heads into the southern India Ocean.
Parts of Madagascar have already been hit by heavy rain, with Sambava in the northeast recording 95mm (3.7 inches) of rainfall on Friday.
The next three days could bring at least an additional 300mm (11.9 inches) to northeastern areas of the country.
Herold is currently located some 800 kilometres (497 miles) to the northwest of Port Louis in Mauritius. It has sustained winds or about 110kmph (68mph) and gusts nearer 140kmph (87mph).
The system is now intensifying explosively, with the winds forecast to reach 195kmph (120mph) gusting up to 240kmph (150mph) by Monday, making it equivalent to a Category 3 Atlantic hurricane on the Saffir-Simpson scale.
The cyclone is expected to pass to the northwest of Mauritius at that peak intensity and then curve to the southwest of Rodrigues Island. Both islands could suffer a significant impact.
Widespread disruption, including the prospect of floods and mudslides, is likely.
There is high confidence in the future track and strength of the storm as it moves extremely favourable conditions in the warm waters. Sea surface temperatures are about 28-29 degrees Celsius (82-84 degrees Fahrenheit).
There is also very little vertical wind shear, which will allow Herold to remain upright and standing. It is likely to remain a powerful system until the mid of the week when it will begin to slowly dissipate.