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Predicted tropical storm frequency

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 the same as are used for the medium range tropical cyclone activity products.  

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1. On Charts page, enter Tropical Storm Frequency
2. Click on Tropical Storm Frequency diagram - Extended Range
   
3. As desired select other base times, or Accumulated Cyclone Energy or Tropical Storm Frequency from drop down menu.

Predicted accumulated cyclone energy (ACE)

Accumulated cyclone energy is the sum of the squares of the estimated maximum sustained velocity of every active tropical storm at six-hour intervals.

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Fig8.2.6-2: The Accumulated Cyclone Energy (ACE) product takes into account number, strength, and duration of all the tropical storms forecast by the extended ensemble during the weekly period within each arbitrarily defined ocean basin, and totals their energy.  This value is compared with a similarly derived ACE from the extended range for the same week to determine the significance level for the given basin.  If this is greater than 90% the basin is shaded.  Green bars represent the forecast and orange bars the real climatology - these can be directly compared.

Tropical storm strike probabilities

This product shows a grid point chart of tropical storm strike probability (probability of a tropical storm passing within 300km), calculated over weekly periods.  It is similar to the tropical cyclone activity charts produced for the medium-range forecasts. 

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 Fig8.2.6-6: Weekly mean anomaly of tropical storm strike probability for the same week as Fig8.2.6-4.  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: 

• Tropical storm weekly mean frequency.  The frequency is derived by comparing the ensemble members probability with that of the 20-year model climatology probabilities within the same 7-day time window.
• Tropical storm weekly mean accumulated cyclone energy (ACE).  This is calculated by summing the square of the estimated maximum sustained velocity of every active tropical storm at six-hour intervals.  The ACE of a time period is the sum of the ACEs for each storm and takes into account the number, strength, and duration of all the tropical storms within the 7-day time window.