Mathieu Rouault et al: Top

Introduction
The nature of southern Africa's surrounding oceans, geographic location and atmospheric dynamics creates an environment conducive to extreme weather. During the 1998/99-summer season, South Africa's Eastern Cape experienced an unusual number of storms, floods and tornadoes. Since most of South Africa's population are living in precarious conditions, the consequences of such floods and tornadoes are often devastating to both people and property. The synoptic situation in the December 14-15, 1998 storm, analysed in this study, appeared to involve interaction between a continental heat low, a South West Indian Ocean anticyclone and an approaching westerly trough and therefore was somewhat different to the heavy rainfall synoptic patterns observed before. This interaction resulted in large regions of organised convection forming over the south of South Africa in the Western Cape and later the Eastern Cape during the storm's lifespan. Initial organisation was circular while the subsequent convection was more linear in form as the storm evolved further. Most of the storm activities was above the adjacent oceanic area. Thunderstorms were observed over the Western Cape, in an area that on average receives less than one thunderstorm per year, and flooding was experienced on December 14 at Tygerhoek. On December 15, heavy rainfall occurred at East London and several tornadoes were reported as the storm moved into the Eastern Cape, one of which caused extensive loss of life and damage at Umtata including threatening the life of South Africa's president at the time, Nelson Mandela. A striking feature was that most of the moisture was coming from the south after a long trajectory above the warm water of the Agulhas Current system

Introduction

The nature of southern Africa's surrounding oceans, geographic location and atmospheric dynamics creates an environment conducive to extreme weather. During the 1998/99-summer season, South Africa's Eastern Cape experienced an unusual number of storms, floods and tornadoes. Since most of South Africa's population are living in precarious conditions, the consequences of such floods and tornadoes are often devastating to both people and property.

The synoptic situation in the December 14-15, 1998 storm, analysed in this study, appeared to involve interaction between a continental heat low, a South West Indian Ocean anticyclone and an approaching westerly trough and therefore was somewhat different to the heavy rainfall synoptic patterns observed before.

This interaction resulted in large regions of organised convection forming over the south of South Africa in the Western Cape and later the Eastern Cape during the storm's lifespan. Initial organisation was circular while the subsequent convection was more linear in form as the storm evolved further. Most of the storm activities was above the adjacent oceanic area. Thunderstorms were observed over the Western Cape, in an area that on average receives less than one thunderstorm per year, and flooding was experienced on December 14 at Tygerhoek. On December 15, heavy rainfall occurred at East London and several tornadoes were reported as the storm moved into the Eastern Cape, one of which caused extensive loss of life and damage at Umtata including threatening the life of South Africa's president at the time, Nelson Mandela. A striking feature was that most of the moisture was coming from the south after a long trajectory above the warm water of the Agulhas Current system

[ Abstract|

Email: rouault@physci.uct.ac.za

Forum

WBC Virtual Poster Session