Abstract 213

Abstract ID: 213

Added value of analysing tropical waves and precipitable water for subseasonal forecast in West Africa : the MISVA platform

Lead Author: Philippe Peyrille
CNRM, Meteo-France, France

Keywords: tropical, waves, Africa, predicatability

Abstract: MISVA – Monitoring and Forecast of Intra-Seasonal Variability over Africa – is a joint research / operational collaborative action between Meteo-France and the West African weather forecasting services from 6 West-African countries together with ACMAD and Aghrymet. Taking advantage of the WMO projects on developing early warning systems (CREWS) in Burkina Faso (2018-2020), Tchad and Togo (2020-2022) , MISVA proposes a web platform with regular updates of subseasonal and synoptic products, a complete documentation of the products and the sience behind. Weekly briefings are hold with the different partners resulting in an expertised weekly bulletin.

To this aim specific products have been developed in a seamless strategy based on the subseasonal ensemble prediction system from ECMWF. Although the skill of ECMWF subseasonal forecast system is limited when using precipitation, the analysis of atmospheric drivers at seasonal, subseasonal scale allows getting a better insight, sometimes beyond week 3 – 4 depending on the atmospheric configuration. In particular two aspect are investigated : i) the analysis of tropical waves using real-time space-time filtering as source of predictability and ii) identifying key parameters with a better predictability than precipitation. For the latter point we take advantage of the tight link between precipitable water and precipitation in the tropics to phrase it in a forecasting perspective. A methodology is defined based on the maximisation of the Heidke Skill Score between observed precipitation and forecast of precipitable water that allows to get a better performance than forecast precipitation at lead time beyond week+4.

An example of operational use of this strategy based on tropical waves monitoring and precipitable water is shown on the anticipation of a humid periods as well as the start and end of the rainy season during the 2019-2022 period.

Thierry Lefort (Meteo-France)
Florence Favot (Meteo-France)