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

Modelling Structure

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

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

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: 1979-2003. 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

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 (1979-2003) 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

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

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

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

DJF forecasts using MOS

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

Predicting Extremes

Operational Seasonal Rainfall Forecast Skill (1999-2004)

Temperature forecast for JJA 2005 issued in May 2005

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

Multi-model ensembles for seasonal prediction

No ENSO, no skill

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