Beginning on November 16, Hurricane Lenny underwent a 24-hour period of rapid deepening, reaching major hurricane status about south of the Mona Passage. It developed well-defined banding features, good outflow, and a circular eye that was visible from the radar in San Juan, Puerto Rico. The hurricane continued to become better organized, with an eye in diameter surrounded by a closed eyewall. Around 1200 UTC on November 17, Lenny intensified into a Category 4 hurricane while approaching the islands of the northeastern Caribbean. It was the fifth storm of such intensity in the year, setting the record for most Category 4 hurricanes in a season. The hurricane then made its closest approach to Puerto Rico, passing about southeast of Maunabo. Shortly thereafter, Lenny attained peak winds of while passing south of the island of Saint Croix in the United States Virgin Islands. This made it the fourth-strongest hurricane on record to form during the month of November. Hurricane Hunters reported Lenny's peak winds in the southeastern portion of the hurricane; the group also reported a minimum pressure of 933 mbar, a drop of 34 mbar in 24 hours. In addition, a dropsonde recorded winds of while descending to the surface, the highest dropsonde wind speed recording in a hurricane at the time.