Reexamination of Tropical Cyclone Wind–Pressure Relationships

Abstract

Tropical cyclone wind-pressure relationships are reexamined using 15 yr of minimum sea level pressure estimates, numerical analysis fields, and best-track intensities. Minimum sea level pressure is estimated from aircraft reconnaissance or measured from dropwindsondes, and maximum wind speeds are interpolated from best-track maximum 1-min wind speed estimates. The aircraft data were collected primarily in the Atlantic but also include eastern and central North Pacific cases. Global numerical analyses were used to estimate tropical cyclone size and environmental pressure associated with each observation. Using this dataset (3801 points), the influences of latitude, tropical cyclone size, environmental pressure, and intensification trend on the tropical cyclone wind-pressure relationships were examined. Findings suggest that latitude, size, and environmental pressure, which all can be quantified in an operational and postanalysis setting, are related to predictable changes in the wind-pressure relationships. These factors can be combined into equations that estimate winds given pressure and estimate pressure given winds with greater accuracy than current methodologies. In independent testing during the 2005 hurricane season (524 cases), these new wind-pressure relationships resulted in mean absolute errors of 5.3 hPa and 6.2 kt compared with the 7.7 hPa and 9.0 kt that resulted from using the standard Atlantic Dvorak wind-pressure relationship. These new wind-pressure relationships are then used to evaluate several operational windpressure relationships. These intercomparisons have led to several recommendations for operational tropical cyclone centers and those interested in reanalyzing past tropical cyclone events.

Climatological aspects of South Pacific tropical cyclones, based on analysis of the RSMC-Nadi (Fiji) regional archive

“…Later, however, an updated methodology for enhanced infrared satellite images (Dvorak 1984) became preferred. This changeover in operational procedure for cyclone intensity estimation was critical because the wind -pressure conversions are quite different for intense tropical cyclones (Table 3), with the earlier Dvorak (1975) method likely being the more correct (Knaff & Zehr 2007). Unfortunately, however, no documentation exists at RSMC-Nadi for fixing the time when the changeover occurred, although the swap was probably implemented after Dvorak himself personally visited the FMS in Fiji in the late 1980s to explain his techniques to regional forecasters (A. Waqaicelua pers.…”

Adapting the Knaff and Zehr wind-pressure relationship for operational use in Tropical Cyclone Warning Centres

“…With such scatter it should come as no surprise that WPRs based upon more limited datasets would arrive at different WPR formulations. The challenge to formulate a new approach to the WPR issue was undertaken by Knaff and Zehr (2007) (hereafter K&Z). They used sixteen years of information (1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004) in the North Atlantic and Central and East Pacific basins including aircraft reconnaissance data, National Hurricane Center's best track estimates and numerical weather prediction (NWP) analysis fields from the National Centers for Environmental Prediction (NCEP).…”

“…The approach of Knaff and Zehr (2007) to account for the scatter in this dataset using the additional parameters of environmental pressure, storm motion, latitude and size represents the most complete WPR devised thus far. Their equation has been modified to be expressed in terms of the radius of gales, POCI (for environmental pressure) and as a ten-minute mean wind speed.…”

Moisture transport by Atlantic tropical cyclones onto the North American continent

“…There is no simple relationship between the size and central minimal pressure of TCs (Emanuel 2005;Knaff and Zehr 2007;Ren et al 2007), therefore we did not attempt to predict the wind radii to extend Schemes 2-4 back in time. Analysis using Scheme 1 is extended back to 1980.…”