Within the South-west Indian Ocean , tropical and subtropical depressions that are judged to have 10-minute sustained windspeeds of 65 km\/h , ( 40 mph ) or more for at least 6 hours by the national weather service of Reunion Island are usually assigned a name . Within the South-west Indian Ocean , tropical and subtropical depressions that are judged to have 10-minute sustained windspeeds of 65 km\/h , ( 40 mph ) or more for at least 6 hours by the Regional Specialized Meteorological Center on La RÃ union Island , France ( RSMC La RÃ union ) are usually assigned a name .