Accuracy of Pressure-Wind Relationships and Dvorak Satellite Intensity Estimates for Tropical Cyclones Determined from Recent Reconnaissance-based "Best Track" Data
Daniel P. Brown, NOAA/NWS/NCEP/TPC, Miami, FL; and J. L. Franklin
For many tropical cyclones, the Dvorak technique is the only operational tool available to estimate the cyclone's intensity (minimum sea level pressure and maximum sustained wind speed). However, when concurrent reconnaissance aircraft data are available, there are often large differences between the Dvorak satellite-based estimates and those determined from the reconnaissance data. Apart from the inherent uncertainty in the technique, discrepancies can occur for many reasons, including uncertainty in the location of the cloud system center of a tropical cyclone, as well as the strict rules and constraints that exist in the Dvorak technique, mainly during initial development and weakening. Conventional wisdom has been that Dvorak intensity estimates are accurate to within half a T-number, or roughly 10-15 kt.
In 1997, reconnaissance aircraft began releasing GPS dropwindsondes into the eyewall or maximum wind band of tropical cyclones. These observations have improved our ability to estimate the maximum surface winds of a tropical cyclone, both by direct measurement and through more accurate interpretation of aircraft flight-level winds. As a result, it is likely that NHC "Best-Track" wind data since 1997 are more accurate than in prior years. Given our current methodology of estimating surface winds from reconnaissance data, two questions are of interest: 1) how accurate are Dvorak intensity estimates, and 2) are previously-determined pressure-wind relationships consistent with current best track data.
In this study, a subset of NHC best track pressure and wind pairs are identified for times when reconnaissance data were available during the period 1997-2001. This subset of the best track is then used to study the performance of satellite intensity estimates and to derive a new pressure-wind relationship for the Atlantic basin.
Session 11C, Tropical Cyclone Best Track
Wednesday, 1 May 2002, 4:00 PM-5:30 PM
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