Global Forecasting Centre for Southern Africa
long-range forecasts for southern Africa
This is a provisional seasonal forecast produced by the Climate Systems Analysis Group (CSAG) at the University of Cape Town (www.csag.uct.ac.za). It is an ensemble mean forecast using a non-standard version of HadAM3. The forecast should be regarded as experimental. It should not be used as a substitute for the official process within the SADC region administered by the Drought Monitoring Centre in Harare; namely the pre-season production of a consensus climate outlook at SARCOF, updates to this outlook, and the refinement and interpretation of the outlook at the national level by national meteorological services. This forecast is provided as is, in a private capacity without any guarantees as to skill or error. The forecast may not be further disseminated, displayed, or publicised in any form without the permission of the seasonal forecasting team at CSAG.
Forecasts provided by CSAG
Latest forecast issued - 23 July 2010.
Notes: We have made changes to the way we do the forecast as well as the variables we include in the forecast.
Firstly,
we have migrated to an updated version of the forecasting model that we used to produce previous forecasts. Please read the box below
the table for information about these changes, the changes are highlighted in blue.
Secondly, we have shortened the forecast to 3 months (or 1 season), we have found very little skill beyond this time horizon using the
persisted sea surface temperature technique we use.
Thirdly, we have elected to include a wind anomaly forecast and exclude the geopotential height and vorticity
variables. We have included some notes on how to interpret the wind forecast on the respective pages. Please contact us at the following email address if you have comments, we would like some feedback:
climate@csag.uct.ac.za.
Our forecasts are made using the United Kingdom Meteorological Office Atmospheric General Circulation Model (AGCM) HadAM3P (older modelwas the HadAM3). The HadAM3P grid resolution is double that of the old model and is now approximately 190x125km (it was approximately 330x250 km). We include the mixed phase precipitation scheme in the model integrations as this improves the model precipitation over southern Africa. A ten member ensemble of the HadAM3P AGCM is integrated forward with observed (Reynolds) sea surface temperatures (SSTs). This ensures that aspects of the model (e.g. soil moisture and temperature) are in equilibrium with the model precipitation as forced by historical SSTs. The 10 model restart dumps at the end of this period are then used to start the 10 member ensemble forecast which is integrated for 3 months (used to be 5 months) into the future using persisted SST anomalies. The forecast atmospheric fields are then taken as the mean of the forecast ensemble minus the mean of a 48 year climatology (this used to be only 15 years) calculated from a 10 member ensemble hindcast (1960-2008). For precipitation the result is divided by the mean of the climatology ensemble and expressed as a percentage of normal. Other fields are expressed as an anomaly from the model climatological mean.
