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Pretoria, South Africa

The South African Weather Service is mandated to issue warnings of hazardous weather events, including those related to heavy precipitation, in order to safeguard life and property. Flooding and flash flood events are common in South Africa. Frequent updates and real-time availability of precipitation data are crucial to support hydrometeorological warning services. Satellite rainfall estimation provides a very important data source for flash flood guidance systems as well as nowcasting of precipitation events for the data sparse regions of the African continent. Although low earth orbiting satellites with microwave instruments provide good quality rainfall estimates, their temporal and spatial resolution are not adequate for time-critical services. Precipitation estimation using geostationary satellites is less accurate, but provides excellent spatial coverage, is updated frequently and is available in real-time. This study compares different ways to use and combine satellite precipitation estimates and numerical weather prediction model fields over the South African domain in order to determine the optimal estimate of precipitation, which can also be applied in real-time to support flash flood guidance. © 2013 by the authors. Source

Ndarana T.,South African Weather Service | Ndarana T.,Johns Hopkins University | Waugh D.W.,Johns Hopkins University
Quarterly Journal of the Royal Meteorological Society | Year: 2010

The climatological link between cut-off low (COL) pressure systems that occur from 20 to 50°S and Rossby wave breaking (RWB) in the Southern Hemisphere (SH) is examined for 1979-2008. It is shown that COLs are associated with either RWB events (89%) or with potential vorticity (PV) intrusions where there is north-south advection of high-PV air (11%). In the vast majority of COLs, the RWB events occur upstream, on or before the day of the COL formation. The evolution of the PV, geopotential heights, static stability, absolute vorticity and temperature advection fields during the COLs are consistent with the formation of high-PV anomalies that induce cyclonic circulations as predicted by theory. RWB plays a key role in producing the split flow associated with COLs in the SH, which in turn produces absolute vorticity anomalies by shear-curvature vorticity conversion, and creates static stability anomalies. The COLs associated with RWB at 330 K are deeper and more persistent than those associated with 350 K RWB and surface processes differ depending on the isentropic surface on which the associated RWB occurs. The seasonality of the RWB and COLs are similar, and is linked to the seasonal march of the westerly jets. © 2010 Royal Meteorological Society. Source

Landman W.A.,Natural Environment Research Council | Landman W.A.,University of Pretoria | Beraki A.,South African Weather Service
International Journal of Climatology | Year: 2012

Southern African December-January-February (DJF) probabilistic rainfall forecast skill is assessed over a 22-year retroactive test period (1980/1981 to 2001/2002) by considering multi-model ensembles consisting of downscaled forecasts from three of the DEMETER models, the ECMWF, Météo-France and UKMO coupled ocean-atmosphere general circulation models. These models are initialized in such a way that DJF forecasts are produced at an approximate 1-month lead time, i.e. forecasts made in early November. Multi-model forecasts are obtained by: i) downscaling each model's 850 hPa geopotential height field forecast using canonical correlation analysis (CCA) and then simply averaging the rainfall forecasts; and ii) by combining the three models' 850 hPa forecasts, and then downscaling them using CCA. Downscaling is performed onto the 0.5° × 0.5° resolution of the CRU rainfall data set south of 10° south over Africa. Forecast verification is performed using the relative operating characteristic (ROC) and the reliability diagram. The performance of the two multi-model combinations approaches are compared with the single-model downscaled forecasts and also with each other. It is shown that the multi-model forecasts outperform the single model forecasts, that the two multi-model schemes produce about equally skilful forecasts, and that the forecasts perform better during El Niño and La Niña seasons than during neutral years. © 2010 Royal Meteorological Society. Source

News Article | April 29, 2016
Site: http://www.reuters.com

JOHANNESBURG (Reuters) - The winter forecast for drought-hit South Africa has become increasingly uncertain as an El Nino weather pattern persists but chances remain for above-average winter rainfall for most of the country, the South African Weather Service said on Friday.

News Article | August 29, 2016
Site: http://www.reuters.com

PRETORIA (Reuters) - South Africa's recovery from its worst drought in over century could be stalled as anticipated rain relief from a La Nina weather system remains uncertain, the South African Weather Service said on Monday.

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