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The charts show the strike probability based on the number of members that predict a tropical cyclone, each member having equal weight. To be counted, the tropical cyclone centre must track within a 300km radius of the location within a time window of 48 hours. The charts are also useful during and after extratropical extra-tropical transition of these features as they move into mid-latitudes. However, the technique can sometimes incorrectly identify as a tropical cyclone a high-latitude circulation containing something of a warm core (e.g. a well occluded frontal depression with cooler air encircling some warm, moist air remnants near the centre). The result will be spurious probabilities of tropical storm strikes. Future improvements to the technique will will aim to remove this problem.
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Tropical cyclone, tropical storm, and hurricane strike probability charts are also available on ecCharts. These are an experimental product based upon identification of the warm-core circulation during the forecast period. They are useful during and after extratropical extra-tropical transition of these features as they move into mid-latitudes. ecCharts have the advantage that boundary layer (or any other) winds can be superimposed.
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