Conditional instability and shear for six hurricanes over the Atlantic Ocean

One hundred and thirty Omega dropwindsondes deployed within 500-km radius o f the eye of six North Atlantic hurricanes are used to determine the magnit udes 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) decrease s to near neutral stability by 75 km from the eyewall. Vertical shears incr ease as radius decreases, but maximum shear values are only one-half of tho se found over land. Scatter for birth the conditional instability and the s hear is influenced chiefly by hurricane intensity, but proximity to reflect ivity features does modulate the pattern. The ratio of the conditional inst ability to the shear (bulk Richardson number) indicates that supercell form ation is favored within 250 km of the circulation center, but helicity valu es 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 vertic al profile of the horizontal wind in a hurricane at landfall.