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Conditional Instability and Shear for Six Hurricanes over the Atlantic Ocean

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  • 1 Department of Meteorology, University of Hawaii, Honolulu, Hawaii
  • | 2 NOAA/AOML/Hurricane Research Division, Miami, Florida
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Abstract

One hundred and thirty Omega dropwindsondes deployed within 500-km radius of the eye of six North Atlantic hurricanes are used to determine the magnitudes and trends in convective available potential energy, and 10–1500-m and 0–6-km shear of the horizontal wind as a function of radius, quadrant, and hurricane intensity.

The moist convective instability found at large radii (400–500 km) decreases to near neutral stability by 75 km from the eyewall. Vertical shears increase as radius decreases, but maximum shear values are only one-half of those found over land. Scatter for both the conditional instability and the shear is influenced chiefly by hurricane intensity, but proximity to reflectivity features does modulate the pattern. The ratio of the conditional instability to the shear (bulk Richardson number) indicates that supercell formation is favored within 250 km of the circulation center, but helicity values are below the threshold to support strong waterspouts.

The difference between these oceanic observations and those made over land by other researchers is evidence for significant modification of the vertical profile of the horizontal wind in a hurricane at landfall.

* Current affiliation: National Hurricane Center, NWS, NOAA, Miami, Florida.

Corresponding author address: G. M. Barnes, Dept. of Meteorology, University of Hawaii, 2525 Correa Road, Honolulu, HI 96822.

Email: garyb@soest.hawaii.edu

Abstract

One hundred and thirty Omega dropwindsondes deployed within 500-km radius of the eye of six North Atlantic hurricanes are used to determine the magnitudes and trends in convective available potential energy, and 10–1500-m and 0–6-km shear of the horizontal wind as a function of radius, quadrant, and hurricane intensity.

The moist convective instability found at large radii (400–500 km) decreases to near neutral stability by 75 km from the eyewall. Vertical shears increase as radius decreases, but maximum shear values are only one-half of those found over land. Scatter for both the conditional instability and the shear is influenced chiefly by hurricane intensity, but proximity to reflectivity features does modulate the pattern. The ratio of the conditional instability to the shear (bulk Richardson number) indicates that supercell formation is favored within 250 km of the circulation center, but helicity values are below the threshold to support strong waterspouts.

The difference between these oceanic observations and those made over land by other researchers is evidence for significant modification of the vertical profile of the horizontal wind in a hurricane at landfall.

* Current affiliation: National Hurricane Center, NWS, NOAA, Miami, Florida.

Corresponding author address: G. M. Barnes, Dept. of Meteorology, University of Hawaii, 2525 Correa Road, Honolulu, HI 96822.

Email: garyb@soest.hawaii.edu

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