Page History

...

These parameters are calculated over the same weekly periods as the other monthly forecast products and are averaged over an ocean basin.  The tropical cyclone identifying algorithms are algorithms are the same as are used for the medium range tropical cyclone activity products.  Evaluation of TC tracks for the Extended range ENS is computed at 6hr intervals in the same way as medium range ENS and the outputs are consistent.

Fig8.2.7-1: To view tropical storm frequency.

...

A further normalisation sets the climatological value (orange) equal to 1.   The forecast value (green) indicates above average (value greater than 1) or below average (value less than 1) Accumulated Cyclone Energy respectively.

...

This product shows a grid point chart of tropical storm strike probability (probability of a tropical storm passing within 300km), calculated over weekly periods.  The charts are based on the number of extended range ensemble members that predict a tropical cyclone, each member having equal weight.  This provides a quick assessment of high-risk areas allowing for some uncertainty in the exact timing or position.  The strike probabilities are generated for three storm categories; tropical depressions (winds >8 m/s), tropical storms (winds >17 m/s) and hurricanes/typhoons (winds >32 m/s).

Three parameters are available:

These charts show the evolution of existing and potential tropical cyclone activity.

• Strike probability chartRaw strike probability.  This is the probability (in %) that a tropical cyclone will pass within a 300 km radius from a given location and within the 7-day time window.   The charts are based on the number of extended range ensemble members that predict a tropical cyclone, each member having equal weight.   It is similar to the tropical cyclone activity charts produced for the medium-range forecasts.  
• Probability anomaly chart.  This shows whether the strike probabilities are higher (red shading) or lower (blue shading) than probabilities within a 20-year model climatology within the same 7-day time window.  They are computed by subtracting the model climatological probabilities from the real-time forecast probabilities.  Mean anomalies of probability are shown by the scale.
• Model extended range climate range climate charts (ER-M-climate) charts show  show weekly mean strike probabilities (in %) within the same 7-day time window.

...

Fig8.2.7-6: Weekly mean tropical storm strike probability of the extended range forecast.  Colours give probability in percentages.

Fig8.2.7-7: Weekly mean tropical storm strike probability deduced from the extended range re-forecasts, for the same week as Fig8.2.7-6.  Colours give probability in percentages.

 Fig8.2.7-8: Weekly mean anomaly of tropical storm strike probability for the same week as Fig8.2.7-6.  Colours give indication of more likely (positive probabilities, red to brown/black), or less likely (negative probabilities, cyan to blue/black) than shown in the extended range re-forecasts.

OpenChart  display

Tropical Storm Probabilities - Extended range forecast

These charts show the evolution of existing and potential tropical cyclone activity.

• Strike probability is the probability (in %) that a tropical cyclone will pass within a 300 km radius from a given location and within the 7-day time window.   The charts are based on the number of extended range ensemble members that predict a tropical cyclone, each member having equal weight. 
• Probability anomaly charts show whether the strike probabilities are higher (red shading) or lower (blue shading) than probabilities within a 20-year model climatology within the same 7-day time window.  They are computed by subtracting the model climatological probabilities from the real-time forecast probabilities.  Mean anomalies of probability are shown by the scale.
• Model extended range climate charts (ER-M-climate) show weekly mean strike probabilities (in %) within the same 7-day time window.

Tropical Storm Frequency - Extended range forecast

These charts show: 

...

.