On the morning o f September 24, Google announced on Twitter that it is releasing the September 2019 core update later today. Core updates impact how Google ranks web sites and how Google determines what is the most relevant web page for a specific query.
Here is the announcement:
Google has given advice on what you can do if your impacted negatively by a core update.
This isn’t the first time that Google has pre-announced a core update. They did pre-announcement for the June 2019 core update.
According to Danny Sullivan, as of this writing, he said that he expected to begin rolling out within the next few hours, then a few days to completely roll out.
Also, it seems that Google’s naming scheme seems to be the name and year. This is because of the confusion over the March core update.