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A Record Minimum Sea Level Pressure Observed in Hurricane Gilbert

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  • 1 Hurricane Research Division, AOML/NOAA, Miami, Florida
  • | 2 Office of Aircraft Operations, NOAA, Miami, Florida
  • | 3 Colorado State University, Fort Collins, Colorado
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Abstract

On 13 September 1988, Hurricane Gilbert attained an extreme minimum sea level pressure, estimated to be 885 hPa from aircraft reconnaissance reports at the time. Postseason analysis indicates that the flight-level pressure, P, upon which this figure is based requires correction upward. In typhoons with sea level pressures <900 hPa, comparison between sea level pressures measured by dropsonde and those estimated by the same method used in Gilbert indicates that, in addition to the error in P, the estimation has a bias toward low pressure. Although the aircraft did not release a dropsonde in the eye at minimum pressure, it is possible to calculate hydrostatic sea level pressures by assuming a variety of plausible thermal structures below flight level. With corrected P, both the statistical extrapolation with its bias removed and the hydrostatic calculations show that a revised value of 888 ±2 hPa is closer to the true minimum sea level pressure. The standard deviation of the various approximations means that the probability is <3% that the actual minimum failed to reach a value below 892 hPa, the old record for a hurricane in the Atlantic Basin set by the Labor Day Hurricane of 1935.

Abstract

On 13 September 1988, Hurricane Gilbert attained an extreme minimum sea level pressure, estimated to be 885 hPa from aircraft reconnaissance reports at the time. Postseason analysis indicates that the flight-level pressure, P, upon which this figure is based requires correction upward. In typhoons with sea level pressures <900 hPa, comparison between sea level pressures measured by dropsonde and those estimated by the same method used in Gilbert indicates that, in addition to the error in P, the estimation has a bias toward low pressure. Although the aircraft did not release a dropsonde in the eye at minimum pressure, it is possible to calculate hydrostatic sea level pressures by assuming a variety of plausible thermal structures below flight level. With corrected P, both the statistical extrapolation with its bias removed and the hydrostatic calculations show that a revised value of 888 ±2 hPa is closer to the true minimum sea level pressure. The standard deviation of the various approximations means that the probability is <3% that the actual minimum failed to reach a value below 892 hPa, the old record for a hurricane in the Atlantic Basin set by the Labor Day Hurricane of 1935.

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