On the pressure-wind relationship in tropical cyclones

A new model for the determination of the pressure-wind relationship in tropical cyclones has been developed. The model is based on storm structure parameters such as central pressure, radius of outermost closed isobar, radius of 34 kt wind speed or maximum wind speed and the radius of maximum wind speed, which are provided operationally by tropical-cyclone advisories. For any pair of storm parameters (e.g. radius of outermost closed isobar and central pressure), the model computes a consistent set of all remaining storm parameters via the gradient wind equation and an artificial, analytical tangential wind profile. The model allows systematic insights in the general relationship between all storm parameters and their range of validity.

The new method has been tested successfully against storm structure information provided by operational tropical-cyclone advisories of the years 2000-2004. Statistical analysis of the model results and comparisons with the operational parameters show agreement in the general characteristics of storm parameter relationships, but also significant differences. For example, the model produces lower maximum wind speeds in the case of strong storms with low values of central pressure. For given radius of outermost closed isobar and central pressure, the mean differences between the model results and the observations amount to 3.5 m/s in maximum wind speed (9770 cases of tropical depressions and storms), 31 km in the radius of maximum wind speed and 47 km in the radius of 34 kt wind speed (5110 cases).

Besides direct application of the new model in an operational context to estimate (or possibly correct) storm structure parameters, it is planned to apply the method for the construction and implementation of more realistic storms in operational numerical prediction models such as the Australian Weather Bureau's Tropical-Cyclone Limited-Area Prediction System.