Updated Prediction of Seasonal Tropical Cyclone Activity over the Western North Pacific and the South China Sea, and the Number of Landfalling Tropical Cyclones over South China


1. Introduction

Issued on 24 June 2003

     This is an update of the predictions of the annual number of tropical cyclones (TCs) affecting the western North Pacific (WNP) and the South China Sea (SCS), as well as the annual number of TCs making landfall along the South China coast for 2003 that we issued on 24 April 2003.  These updates are made based on new information for the months of April and May 2003.  Details of the predictions methods can be found in Chan et al. (1998, 2001) and Liu and Chan (2003).


2. ENSO conditions in 2003

        As discussed in our updated ENSO discussion on 16 June 2003, it is likely that 2003 will be a La Nia year.  All our predictors related to ENSO also suggest a La-Nia-type TC activity (see Table 1).  This is consistent with our 24 April 2003 discussion.

3. Predictions for 2003

        For the entire WNP, the average predictions are almost the same as those issued earlier except perhaps for the number of typhoons, changing from 16 to 15 (Table 1).  This is consistent with the pattern in the past that during La Nia years, the number of typhoons tends to be either normal or below normal (Fig. 1).  Such a pattern is reasonable because during these years, TCs tend to form further west and north (Wang and Chan 2002) so that some of them would have less time to develop.  This situation, though, does not affect the number of weaker systems that much.  As a result, the predicted numbers of tropical cyclones and those reaching at least tropical storm intensity are near normal.

        More TCs tend to form over the SCS during a La Nia year especially in the late season (Wang and Chan 2002).  The predictions shown in Table 1 therefore call for normal to above-normal activity over the SCS, which are again consistent with the patterns in previous La Nia years (Fig. 2).  However, the number of landfalling TCs remains near normal.

To summarize, the updated predictions are:

Western North Pacific

near-normal numbers of tropical cyclones and those reaching at least tropical storm intensity 
normal to below-normal number of typhoons 

South China Sea
 

normal to above-normal numbers of tropical cyclones and those reaching at least tropical storm intensity, especially in the late season 

Landfall over South China 

normal

 


Table 1.

Predictions of the number of tropical cyclones over the western North Pacific and the South China Sea in 2003.

2003

Forecast issued in April

Forecast issued in June

Normal

WNP:

 

 

 

No. of TCs

29 3

30 3

31

No. of TCs with at least tropical storm intensity

26 3

26 3

27

No. of typhoons

16 2

15 2

17

SCS:

 

 

 

No. of TCs

14 2

15 2

13

No. of TCs with at least tropical storm intensity

11 2

12 2

10

No. of TCs making landfall along the South China coast

5 1

5 1

5

 

Fig. 1

Fig. 2


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. Weather 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. Weather Forecasting, 16, 491-498. Abstract

Liu, K. S. and J. C. L. Chan, 2003: Climatological characteristics and seasonal forecasting of tropical cyclones making landfall along the South China coast. Monthly Weather Review (in press)  

Wang, B. and Chan, J. C. L., 2002: How strong ENSO events affect tropical storm activity over the western North Pacific. J. Climate, 15, 1643-1658. Abstract