Hurricane Sergio (2006) - Meteorological History

Meteorological History

A tropical wave crossed Central America and entered the eastern Pacific Ocean on November 7. An area of convection along the wave tracked westward to the south of Central America and Mexico, and became more concentrated on November 12 while located about 400 miles (645 km) south of Acapulco. Later that day, Dvorak classification began on the disturbance, and the convection continued to organize. Early on November 13, the National Hurricane Center indicated the possibility of the system developing into a tropical depression. Thunderstorm activity briefly decreased, though late on November 13 the system acquired enough circulation and organized convection for it to be designated Tropical Depression Twenty-One-E while located about 460 miles (740 km) south of Manzanillo, Mexico. Operationally, the depression was not upgraded until eleven hours later.

Initially, the tropical depression tracked to the northwest, and was forecast to peak as a 50 mph (80 km/h) tropical storm while continuing on a northwest motion. Located within an area of weak wind shear, deep convection increased near the center, and banding features became more pronounced. Anticyclonic flow aloft and a moist troposphere allowed the depression to intensity into Tropical Storm Sergio on November 14. Shortly after becoming a tropical storm, Sergio turned to the southeast, believed to be due to the flow associated with a mid- to upper-level trough to its northeast. It steadily intensified, and Sergio attained hurricane status on November 15 while located about 420 miles (675 km) southwest of Acapulco. With a small, distinct eye located in the center of the deep convection, Sergio rapidly intensified to attain peak winds of 110 mph (175 km/h) about 6 hours after becoming a hurricane.

Upon reaching peak strength, forecasters at the National Hurricane Center predicted Hurricane Sergio to intensify further to reach winds of 120 mph (195 km/h). Shortly after peaking, the hurricane turned to the north and gradually weakened as wind shear from an upper-level trough to its northwest increased. By early on November 17, the low-cloud circulation became partially exposed on the west side of the deep convection, and it is estimated that Sergio weakened to a tropical storm later that day. A ridge to its north and northeast turned the storm to the northwest and later to the west as Sergio gradually weakened. Deep convection reformed near the center on November 18, resulting in a slight increase in winds, though vertical shear quickly weakened it again. Later that day, the storm made its closest approach to land, about 225 miles (360 km) southwest of Michoacán. Early on November 20 it degenerated into a tropical depression, and later that day Sergio dissipated about 360 miles (580 km) southwest of Manzanillo, Mexico, or about 320 miles (515 km) west-northwest of where it originally formed. The remnants of Sergio continued westward for about a day before the minimal amount of convection diminished.