1 Summary of CFS ENSO Forecast September 2010 update Mingyue Chen, Wanqiu Wang and Arun Kumar Climate Prediction Center 1.Latest forecast of Nino3.4 index (slide 2) 2.Hindcast skill of Nino3.4 index (slide 3) 3.Hindcast scatter plots of Nino3.4 index (slide 4) 4.Verification of forecast for August 2010 (slides 5-15) Outline

2 Forecasts from the latest initial conditions show that the current below-normal Nino3.4 SST will be enhanced in the next 5 months. The PDF corrected forecasts show smaller amplitude of ensemble means and smaller spreads among individual forecast members, and the amplitude of cold anomalies will be reduced after Jan Latest Nino3.4 SST forecast from September 2010

3 PDF corrected RMSE (K) Hindcast skill of Nino3.4 index from September initial conditions PDF correction shows much smaller of RMSE during Jan-Jun than un-corrected forecast. Correlation skills of PDF corrected are slightly lower for all months. Correlation PDF corrected

4 Hindcasts of NDJ Nino3.4 index from September initial conditions Raw anomaliesPDF corrected anomalies PDF correction show improvement for NDJ forecast at cold anomalies from September initial condition.

5 Verification of CFS Forecast for August 2010 Nino34 SST: Nino3.4 SST Aug 2010 forecasts show too warm anomalies than the observation from initial conditions of Mar-Apr The forecasts are closed to the observation from initial conditions after Apr PDF corrected forecasts show less cold amplitudes of ensemble means and much less spread among individual members. No clear improvement with PDF correction at lead time beyond 2 months or so (slide 6&7). Spatial SSTs: Anomalies in the tropical E. Pacific, SE Pacific, and NE Pacific from CFS were too warm but those over the NW Atlantic were too cold in the forecasts from Mar 2010 initial conditions. Tropical anomalies around 120W became too cold in the forecasts from initial conditions after Apr 2010 (slides 8-9). Taux and subsurface temperatures: Consistent with the errors in SST, the CFS produced large westerly errors in the western/central tropical Pacific in the forecasts from initial condition of Mar Forecasts for Aug 2010 also showed warm errors in subsurface temperature east of the Date Line (slides 10-13). Impacts of intraseasonal variability: Observed equatorial total 850mb zonal wind anomalies showed intraseasonal variations together with more persisting easterly anomalies in the western Pacific after May 2010 (slide 14, left panel). Forecast Nino3.4 SSTs varied with initial time with below normal anomalies after March initial conditions (slide 14, right panel). The fluctuation of the forecast Nino3.4 SSTs appeared to be related to the intraseasonal (10-70-day) wind variations in the western Pacific (slide 15). The strong easterly anomalies in the W. Pac around late Apr to early May 2010 may have contributed to the sustained easterlies and thus colder SSTs in the forecasts. Similarly, the easterly anomalies around mid July 2010 may have contributed to the enhanced cold anomalies of SSTs in the forecasts from late July The further cold anomalies of SSTs in the forecast from early Sep 2010 may be related to the easterly anomalies on the W. Pac. during that time period (slide 6-11, 14-15). Analysis of forecast for Aug 2010 from previous initial months

6

7

8

9

10

11

12

13

14

15 Intraseasonally filtered anomaly with respect to initial time