|
|
Updated Prediction of Seasonal Tropical Cyclone Activity over the Western North Pacific for 2005
|
1. Introduction |
Issued on 24 June 2005 |
This is an update of the predictions of the annual number of tropical cyclones (TCs) affecting the western North Pacific (WNP) for 2005 that we issued on 27 April 2005. These updates are made based on new information for the months of April and May 2005. Details of the predictions methods can be found in Chan et al. (1998, 2001) and Liu and Chan (2003).
2. ENSO conditions in 2005
Most dynamical models, 10 out of 12, continue to predict ENSO-neutral conditions throughout much of 2005. No obvious precursors that were present in previous warm or cold events can be identified from the current atmospheric and oceanographic conditions. Thus, it is likely that 2005 should be ENSO-neutral. Because of the lack of an obvious forcing from ENSO, it is likely that TC activity will be mainly controlled by factors other than those from ENSO.
3. Predictions for 2005
As discussed in section 1 and Chan et al. (2001), the Apr and May predictors are included in our updated forecasts. It is noted that because NCEP changes the way the WP index is calculated (see http://www.cpc.noaa.gov/data/teledoc/telecontents.shtml), we decided to drop this index as one of the predictors until a more thorough study on the revised index has been completed.
For the total number of TCs, changes in the predictions from two parameters are found. The prediction from the index of the western extent of the subtropical high (HWNP) is 26 compared with 25 in the Apr forecast, which still gives below-normal TC activity (cf. Tables 1a and 1b). A greater increase, from 29 to 31 occurs based on the Nino4 predictor. The final predicted number is therefore increased from 28 to 29.
For the number of tropical storms and typhoons, only the prediction from the index of the strength of the India-Burma trough changes, increasing from 23 to 24. The final predicted number is therefore increased from 24 to 25.
No obvious change for the predicted number of typhoons. All predictors give essentially the same predictions as those from Apr. However, with the drop of the WP index as one of the predictors, the final predicted number becomes 16.
With these changes, the average predictions from all the potential predictors therefore call for a near-normal to slightly below-normal year for all TC categories for the entire WNP.
Summary of predictions
Entire western North Pacific |
|
All TC |
near normal to slightly below normal |
Tropical storms and typhoons |
near normal to slightly below normal |
Typhoons |
near normal to slightly below normal |
| Table 1. | Forecasts from various predictors and the weighted average of the forecasts issued in (a) April and (b) June. |
(a) April Forecast
|
Entire western North Pacific |
||||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||||
(b) June Forecast
|
Entire western North Pacific |
||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||
|
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, 131, 1650-1662. Abstract
