ember months

Comes from the fact that three of the four months end with "-ember".

ember months pl (plural only)

1. (often Nigeria) The final four months of the year: September, October, November, and December.
   • 2017 August 26, “‘Ember Months’ of Tragedy: Separating the Myth from the Facts”, in Leadway‎, archived from the original on 21 September 2019:

     For as long as can be remembered, the end of every year is believed to be synonymous with increased crime rate and road traffic accidents in Nigeria. The last four months, September to December, popularly referred to as the "ember months" because they end with "ember", fall into this category.

• Oxford English Dictionary
• CNN
• pulse.ng
• Leadway