Met-8 Airmass RGB 29 Dec 2020

Ex-Tropical Storm Chalane crosses southern African subcontinent

25 December 2020 00:00 UTC-2 January 2021 09:00 UTC

Met-8 Airmass RGB 29 Dec 2020
Met-8 Airmass RGB 29 Dec 2020

Tropical Storm Chalane was a tropical cyclone that made landfall in Madagascar and Mozambique in December 2020 and crossed the entire South African subcontinent to emerge into the South Atlantic on 3 January 2021.

Last Updated

11 February 2021

Published on

10 February 2021

By Jochen Kerkmann (EUMETSAT)

Chalane affected Madagascar, Mozambique, Zimbabwe, Botswana and Namibia with strong rainfall and heavy winds: up to 351 mm/24 hours fell in Madagascar, seven casualties were reported in Mozambique and 150 mm of rain was reported in central/northern Namibia.

Originally a tropical depression, Chalane strengthened into a Tropical Storm on 24 December. Two days later, on 26 December, Chalane made landfall in Madagascar and weakened, before emerging into the Mozambique Channel on 27 December (see Figure 1).

Figure 1: Meteosat-8 Tropical Airmass RGB, 25 December 2020, 00:00 UTC to 28 December 2020, 00:00 UTC.

Subsequently, Chalane restrengthened, before making landfall in Mozambique on 30 December (in Mozambique’s Sofala province — which had been struck by Tropical Cyclone Idai in March 2019). The system weakened as it moved inland, degenerating into a remnant tropical low later that day. However, Chalane's remnants continued moving westward for another several days (see unusual track of Chalane, Credit: Wikipedia), as can be seen in the animation of the Tropical Airmass RGB (Figure 2).  This RGB is identical to the Airmass RGB, but tuned to tropical conditions (much colder, higher clouds). High clouds appear as ochre, with the highest clouds (overshooting tops) as white.

Figure 2: Meteosat-11 Tropical Airmass RGB, 28 December 2020, 00:00 UTC to 2 January 2021, 00:00 UTC.

The westward journey of ex-Chalane across the African subcontinent can also be monitored using daily Natural Colour RGB images (Figure 3). To help identifying the tropical low, the 850 hPa geopotential is plotted on the satellite images. The system weakened considerably on its way westward, however, it remained strong enough to generate considerable rainfall in Botswana and Namibia, by advecting even more moisture an instability in the region.

Figure 3: Meteosat-11 Natural Colour RGB images, 24 hours time steps, 29 December 2020-2 January 2021 (09:00 UTC). Blue lines denote ECMWF 850 hPa geopotential. Credit: EUMeTrain.

Only a few tropical lows have been observed to travel such a long distance inland bringing substantial rainfall over arid to semi-arid areas like Namibia and Botswana (e.g. tropical cyclone Eline in February 2000 ). In exceptional cases they can traverse the entire breadth of the southern African subcontinent, from the Indian Ocean to the Atlantic coast: like ex-tropical cyclone Bonita in January 1996, and this case, ex-tropical storm Chalane in January 2021.


Related content

Tropical storm Chalane makes landfall in Mozambique (CGTN)
Southern Africa, Flash Update No.4: Tropical Storm Chalane (as of 29 December 2020) (Relief Web)