Status: Ongoing analysis Material from: Linus
1. Impact
It was reported on BBC 14 April about severe rainfall in south-eastern South Africa (https://www.bbc.co.uk/news/world-africa-61092334), killing more than 300 people. The main rainfall seems to have taken place 10-12 April. The rainfall was likely connected to the trough seen at 500hPa with heavy rainfall on the eastern side, mainly over ocean in the short forecast. The La Reunion office classified the system as a tropical cyclone on 12 April.
2. Description of the event
The plots below show MSLP from analysis and 6-hour precipitation forecasts from 9 April 00UTC to 13 April 00UTC, every 12 hour.
The plots below show z500 (contour) and T850 (shade) in analyses from 8 April 00UTC to 13 April 00UTC, every 24 hour.
3. Predictability
3.1 Data assimilation
3.2 HRES
The plots below show observations from SYNOP (first plot), concatenated 6-hour forecasts (2nd plot) and HRES forecasts of 72-hour precipitation valid 10 April 06UTC - 13 April 06UTC, from different initial dates. The black box marks a region around Durban.
3.3 ENS
The plots below show EFI for 3-day precipitation 10-12 April, from different initial times. The forecast from 7 April and earlier had the main signal over sea.
The plot below shows the forecast evolution plot for 72-hour precipitation valid 10 April 06UTC - 13 April 06UTC centered around Durban, South Africa (0.5x0.5 degree box). The forecasts are averaged for the observation locations. Mean of observations - green hourglass, concatenated 6-hour forecasts - green dot, HRES –red, ENS CF – purple, ENS blue box-and-whisker, Model climate – red box-and-whisker. Triangle marks the maximum in the model climate based on 1200 forecasts. Only in the last ensemble, the median was beyond the 99th percentile of the model climatology.
