Severe thunderstorms resulting in flash flooding

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Information about Severe thunderstorms resulting in flash flooding

Published on November 10, 2016

Author: sabcnews

Source: slideshare.net

1. SEVERE THUNDERSTORMS RESULTING IN FLASH FLOODING WREAK HAVOC IN GAUTENG Severe thunderstorms resulting inheavy downpours and flash flooding, hit parts of Gauteng on the afternoonof the 9th November 2016. Areas that were most affectedwere the City of Johannesburg and Ekurhuleni MetropolitanMunicipalities. This comes twodays after isolatedsevere thunderstorms resultedinflashflooding in the Silver Lakes areain Pretoriaas well as inareas inBuccleuch, Edenvale and Bedfordview. Damage to property was reported, which included OR Tambo International Airport where there were also some flights which were either diverted or delayed. Major roads were affectedandthere were cars submerged or swept away on the R24, N3 and N12 highways, (see figure 1 below). At this stage at least 4 fatalities have been reported. The South African Weather Service hereby expresses its condolences and sympathy to those who have lost their lives and property during this extremely severe weather event. SUMMARY AND DISCUSSION A watch for severe thunderstorms was issued at 14:15 for the southern parts of Gauteng. This watch was escalated to a warning for severe thunderstorms with heavy downpours and small hail at 16:33 for the following areas:

2.  Midvaal, moving towards Lesedi and southern Ekurhuleni.  17:23: City of Johannesburg and Ekurhuleni. The first signal that indicated that the alert was justified, was the development of a band of thunderstorms observed via satellite and radar imagery, moving into the area during the late afternoon from about 14:00 local time onwards. These severethunderstorms produced heavy rain within a short space of time, which subsequently lead to flash flooding. UPCOMING EXPECTED WEATHER Further rainfall is expected today and tomorrow over the North Eastern Free State, KwaZulu-Natal, Gauteng, Mpumalanga, eastern North West and Limpopo, until the weekend. There still remains a very high risk of heavy rain which will result in flooding in more places during this period. Heavy rains are expected tomorrow, 11 November 2016 over:  North-eastern Fee State,  Western parts of KwaZulu-Natal,  Gauteng,  Mpumalanga,  Eastern parts of North West  and southern Limpopo WHAT DOES A SEVERE THUNDERSTORM WARNING MEAN? A severe thunderstorm warning is issued when a thunderstorms contains one or more of the following severe weather criteria:  Hail of greater than 19mm diameter or large amounts of small hail  A tornado  Wind gusts 50 kts (93 km/h) or more  Heavy downpours leading to localised urban or flash flooding PRECAUTIONS TO TAKE DURING FLOODING  If walking outdoors, avoid crossing rivers and swollen streams where water is above your ankles.

3.  Just 15cm of fast-moving flood water can knock a person off their feet, and a depth of 60cm feet is enough to float a car.  Never try to walk, swim or drive through fast-moving flood water. Stop, turn around and go another way.  Listen to the special warnings on radio and/or television  Abandon your home immediately if evacuation is recommended, before access is cut off by flood water.  Never drive into water covering the road. You would not know how deep it is or if the road has been washed away.  If the vehicle stalls, leave it immediately and seek higher ground  Be especially cautious at night when it’s harder to recognize flood dangers. The South African Weather Service will continue to monitor any further developments relating to this weather system and will issue subsequent updates as required. Furthermore, the public is urged to regularly follow weather forecasts on television and radio. Updated information can also be found at www.weathersa.co.za as well as via the SA Weather Service Twitter account @SAWeatherServic

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