There will be no 30 December in Samoa, or Tokelau, a group of three atolls in the Pacific that are territory of New Zealand. They will redraw the international date line at midnight on 29 December, with both jumping straight to 31 December. It's to facilitate commerce with New Zealand and Australia. Wellington and Sydney will now be one and three hours earlier than Samoa and Tokelau, respectively.
Here's how the Samoan Prime Minister explains the rationale: "In doing business with New Zealand and Australia, we're losing out on two working days a week. While it's Friday here, it's Saturday in New Zealand, and when we're at church on Sunday, they're already conducting business in Sydney and Brisbane."
Interestingly, American Samoa is staying right where they are, so although the two territories are only 30 miles apart, the time difference between them will be an entire day.