Multivariate ENSO index. Basically a more comprehensive way to measure the impact of ENSO on the ocean and atmosphere. The current MEI is basically “warm neutral” vs strong Nino pacific SSTs.
Great blog on those euro forecasts for a week December strat vortex.
https://simonleewx.com/2023/11/03/whats-that-coming-over-the-hill-is-it-a-weak-vortex/