ERA-Interim production stopped on 31st August 2019
For the time being and until further notice, ERA-Interim (1st January 1979 to 31st August 2019) shall continue to be accessible through the ECMWF Web API. Keeping in mind that ERA-Interim is published with an offset of about three months from the dataset's reference date, ERA-Interim August 2019 data will be made available towards the end of October 2019.
ERA5 is now available from the Climate Data Store (CDS) (What are the changes from ERA-Interim to ERA5?) and users are strongly advised to migrate to ERA5 (How to migrate from ECMWF Web API to CDS API).
The ERA-Interim dataset is made available for download with an offset of about three months from the dataset's reference date. So January data are available towards the beginning of April, February data are available in May and so on.
For the latest available date please see the ECMWF data server page for ERA-Interim. There is no automatic way of checking the latest available date.
The delay is due to two factors: First, the release is delayed for two to three months to allow for production of the latest data, quality assurance and potential technical issues. Second, since data is released monthly, a dataset produced just after a release date will only be included in the next month's release. These add up to an overall delay of about three months.
For more information on ERA-Interim please see the ERA-Interim page at ECMWF.