Verification of Forecasts of Tropical Cyclone Activity over the Western North Pacific in 2000

Issued in Jan 2001


        In April 2000, we issued forecasts based on the scheme developed by Chan et al. (1998), which will be labeled as the original CSL scheme.  The forecasts called for a slightly above-normal season for the entire western North Pacific but close to normal over the South China Sea (see Table).  Since then, we developed two modifications of the original scheme by incorporating new predictors that appear to be better proxies of the El Nio/Southern Oscillation (ENSO).  One modification (the mCSL-4 scheme) still uses parameters from April of the previous year to March of the current year.  The other modification (the CSL-6 scheme) makes use of parameters from June of the previous year to May of the current year.  These modifications have been written up in a paper (Chan et al. 2001) that is currently under review.  Both modifications are for a slightly above-normal season but with slightly below-normal number of typhoons (see Table).  The predictions from the CSL-6 scheme were issued in June 2000.

        Verification of the forecasts shows that if all those TCs that were considered by JTWC as having reached tropical storm intensity are counted, the predictions from both the mCSL-4 and CSL-6 schemes are all correct.  Even if the three relatively weak TCs (16W, 27W and 28W) are discounted, these revised predictions are still better than the original ones.  In particular, the predicted number of typhoons is much reduced, as observed.

 


References

Chan, J. C. L., J. E. Shi and C. M. Lam, 1998:  Seasonal forecasting of tropical cyclone activity over the western North Pacific and the South China Sea. Wea. Forecasting, 13, 997-1004. Abstract

Chan, J. C. L., J. E. Shi and K. S. Liu, 2001:  Improvements in the seasonal forecasting of tropical cyclone activity over the western North Pacific.  Wea. Forecasting (conditionally accepted)

 


Table.  Forecasts of TC activity in 2000 using the original CSL scheme, the mCSL-4 and CSL-6 schemes.

The asterisk in the TSYA row indicates that 3 TCs were classified by JTWC as tropical storms (16W, 27W and 28W) but they were not named by any other center.  Similarly, the double asterisks in the TSYS row indicate that 1 TC was classified by JTWC as a tropical storm (28W) but not named by any other center.  In the TYA row, the # sign indicates that the 15th typhoon (Soulik) did not intensify to typhoon strength until 3 January 2001(but formed on 29 December 2000).  The observed and normal (1959-94) numbers are also included in the last two columns.

2000

Forecast

Observed

 

Normal

 

Original

mCSL-4 CSL-6

Western North Pacific 

No. of TCs ( TCA )

30 3

32 3

33 3

34

31

No. of TCs with at least tropical storm intensity ( TSYA )

29 3

26 3

28 3

23 / 26*

27

No. of typhoons ( TYA )

22 2

14 2

16 2

14 / 15#

17

South China Sea

No. of TCs ( TCS )

13 2

11 2

13 2

12

13

No. of TCs with at least tropical storm intensity ( TSYS )

10 2

9 2

9 2

7 / 8**

10