The storm formed over the Coral Sea to the south of the Solomon Islands, then intensified to Category 3 force due west of Vanuatu on Monday.
Nickel-mining operations were briefly halted on the French overseas territory of New Caledonia as heavy rain and winds lashed the northwest of the island on Tuesday.
But Sandra lost its tropical characteristics and weakened to the west of New Caledonia the following day.
The combined weather system was expected to merge with another area of low pressure to bring heavy rains to northern New Zealand late in the week.
The North Island has been suffering from a protracted dry spell so far this year and could use the rainfall.
Cyclone Sandra Track
Satellite Loop Data: CIMSS