On 07SEP95, Hurricane Luis intensified from about 100 kt winds and 940 mb minimum sea-level pressure (MSLP) to 120 kt and 935 mb MSLP as it moved northwestward away from the Lesser Antilles. During the course of the day (UT) an outer concentric eyewall formed surrounding the original eyewall at 50 nmi radius. Early on 08SEP95, the new eyewall became the dominant feature and the maximum winds decreased to about 100 kt again. Natural eyewall cycles such as Luis' are virtually identical to the expected result of the STORMFURY modification experiments carried out in the 1960s. Two radar composites transmitted in real time from a NOAA research aircraft to forecasters at the National Hurricane Center shows Luis' well defined outer eyewall surrounding the dissipating partial inner eyewall at 1633-1658 UT and at 1906-1932 UT. More profound weakening through a similar eyewall replacement was the most important factor in avoiding a major disaster when Hurricane Opal approached the Gulf Coast after attaining a MSLP of 916 hPa overnight 03-04OCT95.