Single cell thunderstorm cloud

Severe convective storms over South Africa

27 November 2009 00:00 UTC

Single cell thunderstorm cloud
Single cell thunderstorm cloud

Severe convective storms over the southeastern parts of South Africa.

Last Updated

31 May 2022

Published on

26 November 2009

By Estelle de Coning (South African Weather Service), Jochen Kerkmann (EUMETSAT) and Martin Setvak (CHMI)

The online South African newspaper News24 reported on Friday, November 27 2009, that a thunderstorm had battered KwaZulu-Natal. It was reported that a hail storm accompanied by heavy wind left at least 1,256 people homeless, about 50 people injured and 600 houses damaged. This storm followed another severe thunderstorm which hit a similar area earlier in November 2009. The damage from these and other disasters which have hit this province in the past few weeks, is estimated at 400 million Rand.

Early in the morning of 27 November, the severe convection event was already evident on MSG imagery. The overshooting top associated with the strongest updrafts is clearly visible (see RGB HRV, HRV, IR10.8 at 8:15 UTC). About two hours later, at 10:00 UTC, the convective storm had moved towards Swaziland developing a distinct cold U-shape cloud top, which is a well-known satellite indicator for possible severe weather (see images below).

At the same time, new convective storms were forming to the west (upstream) of the original storm expanding considerably in the following hours into a line of severe convective storms (see Animation, 08:00–14:00 UTC). The convective storms developed in the exit region of an upper level jet streak and in the proximity of a low-level moisture boundary (see Interpretation , and 200hPa wind field at 09:00 UTC, Unified Model). In addition, the storms exhibited rapid growth with strong updrafts as shown by the orange colour in the Day Microphysics RGB (see e.g. RGB VIS0.8, IR3.9r, IR10.8 at 12:00 UTC).

It should be noted that the South African Weather Service (SAWS) is running a local version of the Hydroestimator (NOAA/NESDIS) for nowcasting purposes (see hourly rainfall estimates for the passage of the storm). Rainfall rates of more than 20mm per hour were indicated. There is a good correlation between the rainfall rates shown here and the areas indicated in the satellite imagery at the time. None of the rainfall totals could unfortunately be verified with rain gauges on the surface.

Finally, Aqua MODIS captured the convective storms at about 11:47 UTC (see image below), at a time when the cold-U shape had already disappeared. However, the interesting thing in the MODIS image is the higher-reflectivity plume or diverging shield of cirrus originating south-south-east of the storm core (see band 7 image (2.1 microns) below). Unfortunately, the A-Train missed the storm, crossing the region of storms somewhat further east.

Met-9, 27 November 2009, 10:00 UTC
Figure 1: Meteosat-9 Channel 09 (IR10.8), 27 November 2009, 10:00 UTC. Full Area. Interpretation
Met-9, 27 November 2009, 10:00 UTC
Figure 2: Meteosat-9 Severe Weather RGB, 27 November 2009, 10:00 UTC. Full Area. Animation (08:00–14:00 UTC)
Met-9, 27 November 2009, 10:00 UTC
Figure 3: Meteosat-9 Airmass RGB, 27 November 2009, 10:00 UTC. Full Area
Met-9, 27 November 2009, 10:00 UTC
Figure 4: Meteosat-9 Dust RGB, 27 November 2009, 10:00 UTC. Full Area
Severe convective storms over South Africa
Figure 5: Aqua, MODIS RGB Composite Bands 01-07-31 (VIS0.6, NIR2.1, IR11.0), 27 November 2009, 11:47 UTC. Full Area. Band 01 (VIS0.6). Band 07 (NIR2.1). Band 31 (IR11.0)