In order to respond to a need from the scientific community and users for a “seamless” forecast linking short and medium range forecasting to seasonal forecasting, intra-seasonal forecasting methodologies are being developed. A forecasting methodology on a monthly and regional scale for the French overseas territories, giving way to human expertise, has been developed in the framework of a collaboration between ENM (Ecole Nationale de Météorologie) and CNRM (Centre National de Météorologie). This methodology involves human expertise and the physical concepts of intra-seasonal actors. The experts are studying MJO (Madden-Julian Oscillation) indices, equatorial wave filtering products, MJO composite maps and multi-set numerical outputs. The eventual aim is to produce a synthesis in the form of a written technical bulletin and a user-oriented bulletin. The method is what the experiments led to at the end of 2020 after a few years of practice in territories such as Africa, the Indian Ocean and the maritime continent. The main lines of the method are: low frequency analysis (seasonal), intra-seasonal analysis of the MJO (beyond the RMM index), monitoring of equatorial waves and a fine analysis by weather regime.

The experimentation of this methodology (which is not fixed) was launched in 2018 for the southwest Indian Ocean with a working group between ENM, CNRM and DIROI in the form of monthly briefings. From an upstream research perspective, the PISSARO project has integrated this experimentation and, in partnership with DIROI, has been conducting monthly briefings on the monitoring of the MJO and equatorial waves for the monthly forecast in the south-west Indian Ocean since the 2020-2021 season. The objective is to be able to transcribe, for the general public or users, the technical information produced at the end of each briefing. At the end of each season, a return of experience will be organised to assess the season of this experimental monthly forecasting activity in the south-west Indian Ocean and to reflect on its application for users.

To go further…

Thierry Lefort and Philippe Peyrillé (2020). The 2020 monsoon over Asia and Africa: how well the S2S performed. S2S Newsletter, No. 15, 1-12.