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Dropwindsonde Observations of the Environmental Flow of Hurricane Josephine (1984): Relationships to Vortex Motion

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  • 1 NOAA/AOML/Hurricane Research Division, Miami, Florida
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Abstract

Omega dropwindsonde (ODW) observations from three synoptic-flow experiments in environment of Hurricane Josephine have been analyzed in a research mode using an objective analysis procedure. The nominal times of the analyses are 0000 UTC 10, 11, and 12 October 1984. The filtered, three-dimensional analyses have been used as a basis for several diagnostic and prognostic calculations relating to the motion of the hurricane.

Examination of Josephine's environment revealed a strong variability of the flow with distance from the storm center and with pressure. Josephine moved at right angles to the azimuthally averaged wind at 500 mb; the vortex motion was more consistent with the flow near 700 mb. Forecasts made with a barotropic forecast model showed a high sensitivity of the forecast track to the vertical layer used in the initial analysis. These results demonstrate the potential value of vertical sounding information from the ODWs, and show that single-level midtropospheric information is not always representative of a hurricane's environment flow.

On each of the three days, the motion of Josephine deviated significantly from its environmental “steering,” as measured by an azimuthal average of the 300–850 mb mean flow over the 5°–7° radial band. This deviation from steering (the so-called “propagation” vector) was oriented with components parallel and to the left of the gradient of absolute vorticity in the asymmetric wind field. The magnitude of the propagation was proportional to the strength of the absolute vorticity gradient. These results are consistent with many barotropic modeling studies.

Abstract

Omega dropwindsonde (ODW) observations from three synoptic-flow experiments in environment of Hurricane Josephine have been analyzed in a research mode using an objective analysis procedure. The nominal times of the analyses are 0000 UTC 10, 11, and 12 October 1984. The filtered, three-dimensional analyses have been used as a basis for several diagnostic and prognostic calculations relating to the motion of the hurricane.

Examination of Josephine's environment revealed a strong variability of the flow with distance from the storm center and with pressure. Josephine moved at right angles to the azimuthally averaged wind at 500 mb; the vortex motion was more consistent with the flow near 700 mb. Forecasts made with a barotropic forecast model showed a high sensitivity of the forecast track to the vertical layer used in the initial analysis. These results demonstrate the potential value of vertical sounding information from the ODWs, and show that single-level midtropospheric information is not always representative of a hurricane's environment flow.

On each of the three days, the motion of Josephine deviated significantly from its environmental “steering,” as measured by an azimuthal average of the 300–850 mb mean flow over the 5°–7° radial band. This deviation from steering (the so-called “propagation” vector) was oriented with components parallel and to the left of the gradient of absolute vorticity in the asymmetric wind field. The magnitude of the propagation was proportional to the strength of the absolute vorticity gradient. These results are consistent with many barotropic modeling studies.

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