How skilful are Nowcasting Satellite Applications Facility products for tropical Africa?

Abstract

Satellite nowcasting potentially provides a vital opportunity to mitigate against the risks of severe weather in tropical Africa, where population growth and climate change are exposing an ever growing number of people to weather hazards. Numerical weather prediction demonstrates limited skill for much of Africa and weather radars are rare. However, geostationary satellites provide excellent spatial and temporal coverage of the often long-lasting convective storms that deliver heavy rain, lightning and strong winds, presenting a valuable opportunity for satellite nowcasting. Here, we evaluate the skill of satellite nowcasting products for tropical Africa: these products are routinely generated, but to our best knowledge never routinely used in tropical Africa before the Global Challenges Research Fund African SWIFT (Science for Weather Information and Forecasting Techniques) project. Focusing in particular on convective rainfall rate (CRR) and rapidly developing thunderstorm convection warning (RDT-CW) products, we demonstrate that both are useful nowcasting tools. The CRR product produces very different rainfall climatologies for day and night in tropical Africa. This is associated with greater skill of the product during daytime, particularly for heavier rain rates. The RDT-CW product is able to identify around 60% of heavy (>5 mmÁhr −1) rainfall events with the fraction detected increasing with increasing rainfall rate. For both products, extrapolation forwards in time (up to 90 and 60 min, respectively) maintains useful skill in tropical Africa, motivating work to develop longer lead-time nowcasts. We conclude that widespread uptake of satellite nowcasting could provide new skilful weather predictions on short timescales in much of tropical Africa.

Nowcasting tracks of severe convective storms in West Africa from observations of land surface state

“…Favourable (dry) upstream soil conditions increase the likelihood of an MCS propagating further overnight. The combination of storms which are both long-lived and sensitive to slowly varying land state opens up the possibility for skilful nowcasting of MCSs tracks out to many hours, substantially longer than conventionally attempted [32,39].…”

“…Imagery from geostationary satellites is therefore crucial in identifying active MCSs. Operational forward-tracking of satellite imagery has skill out to at least 90 min in the region [39], whilst new techniques indicate an extension of skill out to at least 4 h [40]. Predictability from extrapolation of existing systems is stronger overnight, when larger, organised and long-lived systems dominate.…”

'I think I discovered a military base in the middle of the ocean' -- Null Island, the most real of fictional places

“…We believe this omission in some ways contributes to its 'mystical nature'. Most academic studies that mention Null Island use it in place of (0, 0) location (Mound et al 2019, Dijt and Mettes 2020, Hill et al 2020, Stein et al 2020, Grégoire et al 2021, Hakima and Bazzocchi 2021, Kousis et al 2022, and only a handful studies go beyond this simplistic view to mention Null Island in relation to its original purpose: to trap geocoding errors (Janowicz et al 2016, Kopsachilis andVaitis 2021). Null Island's history and purpose was also described in an architectural design article by Dillon (2021).…”

Weather, Vol. 77, no. 7, July 2022, pp. 230–268

“…Communication between the University of Leeds/NCAS and NWC SAF is ongoing and there is mutual interest in collaboration on the development/evaluation of NWCSAF/GEO and the delivery of training in Africa. SWIFT NWCSAF/GEO evaluation work conducted at the University of Reading (Hill et al, 2020) helps us understand how NWCSAF/GEO products should be used over Africa. The role of ACMAD within SWIFT will help to generate interest in using NWCSAF/GEO products and provide a pathway for future training in Africa.…”