An Evaluation of the Dvorak Technique for Estimating Tropical Cyclone Intensities from Satellite Imagery.

This paper investigates the accuracy of tropical cyclone intensity estimates as derived from the Dvorak technique. Estimates of current intensity and 24-hour forecast intensities were verified against JTWC official best track data. Results from a 396-case sample indicate overall absolute and bias errors of less than one CI number, even though forecast intensity errors were twice that of the current intensity estimates. Comparison of Dvorak and JTWC intensity errors indicate that they are essentially equal. The Dvorak 24-hour forecast intensities are also superior to all objective forecast aids available to the JTWC. Dvorak forecast data were also evaluated as a function of the tropical cyclones life cycle. Results show a tendency of the Dvorak technique to over-forecast developing and weakening trends. Verification of cases which included a PLUS or MINUS symbol indicated no improvement over cases with no symbols. However, the use of the symbols is believed to reduce forecast intensity error. Author