1. Seasonal Prediction Activities at the South African Weather Service
Willem A. Landman
Asmerom Beraki, Mary-Jane Kgatuke, Maluta Mbedzi and Francois Engelbrecht (UP)
Afrikaans, English, Sepedi/Setswana

2. Modelling Structure

3. CCA forecasts of 1. Nino3.4, and 2. equatorial Indian Ocean SST

4. Multi-tiered system:
Predicted SSTs, forcing COLAT30
GCM output statistically recalibrated with perfect prognosis to rainfall regions

5. Conformal-Cubic Atmospheric Model (CCAM)
Runs performed on a computer cluster at the University of Pretoria (additional runs also being conducted on NEC SX-8 at SAWS)
Climatological ensemble runs - 12hr LAF (5 members completed of 24 planned)
Atmospheric initial conditions for climatological runs obtained from NCEP reanalysis data
Climatological simulations performed for the period: Lower boundary forcing from AMIP SST and sea-ice
Operational Extended-Range Forecasting
One 40-day simulation performed each day (implying 24hr LAF for the construction of ensemble forecasts)
Initial conditions and lower boundary forcing obtained from the GFS 0Z analysis on a daily basis
Persistence of SST anomalies over the 40-day integration period
Operational Long-Range Forecasting (month and seasonal)
10-member ensemble 6-month integrations using persisted and forecast SSTs

6. ECHAM4.5 GCM Ensemble Prediction System Configuration
All runs performed on NEC SX-8
Climatological (6 members) and operational ensemble runs - 24hr LAF
Atmospheric initial conditions from ECMWF (1979 to 1996) analysis
Climatological dataset ( ) constructed using AMIP physics; model constrained by lower boundary conditions generated from a high resolution AMIP2 dataset for SST and sea-ice
Operational set-up: persisted and forecast SSTs obtained from a high resolution observed SST (optimum interpolation v-2) and IRI (mean) respectively (6 members each)
12-member ensemble operational runs on 18th of each month for 6 consecutive months (i.e., 0-5 months lead-time)
Operational seasonal forecasts for 3 consecutive rolling seasons

9. DJF MOS-PP forecast made early December
Small chance of
above-normal
Oceanic Nino Index
Enhanced probabilities
“Normal to below-normal” most likely
The MOS-PP-ECHAM4.5 system was successful in predicting enhanced probabilities of above-normal over the central-western parts and enhanced probabilities in below-normal over the south-western parts, but predicted only small probabilities of above-normal over the north-eastern parts

10. October-November-December
2006
Forecast made in September 2006 By one of the forecast systems developed at the SAWS

11. CCA: evolutionary features (EEOF) of SSTs predicting rainfall
(Forecast made in November 2006 – SSTs up to October 2006)
2006/07

12. DJF forecasts using MOS

13. DJF forecasts using RCM
First ever operational regional climate model forecast for southern Africa
ECHAM4.5-RegCM3
Test period: 1991/92 – 2000/01

14. Predicting Extremes

15. Operational Seasonal Rainfall Forecast Skill (1999-2004)

16. Temperature forecast for JJA 2005 issued in May 2005

17. Multi-model system at the SAWS
Combination
SSTs
Multi-model ensemble
Persisted
Forecast
GCMs
Post-processing
ECHAM4.5
CCAM
Model Output Statistics

18. Multi-model ensembles for seasonal prediction

19. No ENSO, no skill

20. Summary SAWS has multi-tiered forecasting system: GCMs:
Predicting/persisting SSTs
GCMs and RCM
MOS applied to GCM
GCMs:
Operational – ECHAM4.5
Testing phase – CCAM
Statistical methods:
CCA to predict rainfall
MOS (CCA)
Skill (rainfall):
Model skill largely dependent on ENSO
Mainly restricted to summer seasons