Complex sentence: On 31 August 2015, Jetstar announced it had selected the first four regional centres it would serve at the commencement of operations on 1 December; these were Napier, Nelson, New Plymouth and Palmerston North.
Split into simpler sentences: On 31 August 2015, Jetstar announced it had selected the first four regional centres it would serve at the commencement of operations on 1 December. Those selected were Napier, Nelson, New Plymouth and Palmerston North.