Hurricane Lenny - Meteorological History

Meteorological History

Hurricane Lenny began as a low-pressure area that was first observed in the southwestern Caribbean Sea on November 8. It developed an area of convection but remained poorly defined for the next few days. Thunderstorms spread across the region, producing heavy rainfall in portions of Mexico and Central America. On November 13, the system became better organized; a Hurricane Hunters flight later that day discovered a surface circulation and winds of about 35 mph (55 km/h). The data indicated the development of Tropical Depression Sixteen at 1800 UTC, about 175 mi (280 km) south of the Cayman Islands. The depression's convection was fairly disorganized, and the National Hurricane Center (NHC) did not anticipate any strengthening for three days. For much of its existence, the tropical cyclone maintained a track from west to east across the Caribbean Sea, which was unprecedented in the Atlantic hurricane database. The path resulted from its movement along the southern end of a trough over the western Atlantic Ocean.

After its formation, the depression gradually became better organized; the NHC upgraded it to Tropical Storm Lenny on November 14, based on reports from the Hurricane Hunters. When it was first upgraded to a tropical storm, the cyclone already had winds of 65 mph (100 km/h) and a developing eye feature. At 0000 UTC on November 15, Lenny attained hurricane status about 175 mi (280 km) southwest of Kingston, Jamaica. The quick intensification was unexpected and occurred after a large area of convection blossomed over the center. At the same time, Lenny developed an anticyclone aloft, which provided favorable conditions for the hurricane's development. After moving east-southeastward during its initial development stages, the hurricane turned more to the east on November 15. The Hurricane Hunters reported winds of 100 mph (160 km/h), which indicated that Lenny had become a Category 2 on the Saffir-Simpson Hurricane Scale. However, the cloud pattern subsequently became less organized as the eye disappeared, and Lenny's winds weakened to 85 mph (140 km/h) while the hurricane passed south of Hispaniola. The NHC noted the deterioration could have been due to a disruption of the storm's small inner core by "subtle environmental changes". After the sudden weakening, the Hurricane Hunters reported the eye had reformed and that the hurricane's winds had reached 100 mph (160 km/h). At the time, a ridge was expected to build to Lenny's east and turn the storm northeastward into Puerto Rico 24 hours later.

Beginning on November 16, Hurricane Lenny underwent a 24-hour period of rapid deepening, reaching major hurricane status about 165 mi (265 km) 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 29 mi (46 km) 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 75 mi (121 km) southeast of Maunabo. Shortly thereafter, Lenny attained peak winds of 155 mph (250 km/h) while passing 21 mi (33 km) south of the island of Saint Croix in the United States Virgin Islands. This made it the second-strongest hurricane on record to form during the month of November. At the time, Lenny was also one of only four November major hurricanes, but it was later joined by Hurricane Michelle in 2001 and Hurricane Paloma in 2008. 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 210 mph (339 km/h) while descending to the surface, the highest dropsonde wind speed recording in a hurricane at the time.

Around the time it peaked in intensity, Lenny's forward speed decreased in response to light steering currents between two ridges. Despite favorable conditions for strengthening, the hurricane weakened as it turned to an eastward drift, possibly due to the upwelling of cooler waters. Late on November 18, Lenny's eye moved over Saint Martin with winds of 125 mph (205 km/h). After continued weakening, the hurricane struck Anguilla and Saint Barthélemy the next day. It turned southeastward while still drifting, bringing heavy rainfall and strong winds to the islands across the northeastern Caribbean. Late on November 19, Lenny weakened to tropical storm intensity after increased wind shear exposed the cyclone's center from the deepest convection. Early on November 20, the storm made landfall on Anguilla, although by then the center had become difficult to locate. Later that day, the cyclone exited the Caribbean, continuing its southeast track. On November 21, Lenny turned to the northeast and weakened to a tropical depression. The deep convection was located at least 100 mi (160 km) east of the increasingly elongated center. Lenny turned to the east for the final time early on November 22, dissipating the next day about 690 mi (1110 km) east of the Lesser Antilles.