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These plots are derived in a similar way to the equivalent plots used for the extended (monthly) time ranges.  The number of storms in the forecast ensemble are scaled multiplicatively so the model forecast climatology is realistic when compared to observations.  For the northern hemisphere basins, the scaling is based on a comparison of model with observations in a moving interval of the previous 10 years.  This helps ensure that low-frequency variability in tropical storm numbers is adequately represented.  For southern hemisphere basins, where such variability is not a problem and where sampling uncertainties are larger, the calibration uses the full period 1993 to the previous year.  The scaling in both cases is based on the mean of the central two quartiles of data, thus reducing the impact of extreme seasons on the calibration.  Observational data is taken from IBTrACS4, selecting the NHC and JTWC wind speed estimates to give consistency across basins. Forecasts are available for number of tropical storms, number of hurricanes/typhoons, and accumulated cyclone energy (ACE).  Storms are allocated to the basin in which they first form.  ACE is allocated to the basin in which the storm is present at each point of its trajectory.

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