Tropical Storm Karina (2008) - Meteorological History

Meteorological History

Tropical Storm Karina originated from the southern portion of the tropical wave—a tropical wave is an elongated low pressure area embedded within the easterly trade winds—that also spawned Hurricane Gustav in the Caribbean Sea. The wave crossed Central America and entered the eastern Pacific basin on August 28. After two days, the wave spawned an area of low pressure south of Manzanillo, Mexico. The low was located beneath an area of moderate convection, but was nearing cooler waters and a moist, yet stable, air mass. By later that night, a low-level circulation developed partially underneath deep thunderstorm activity. In an area favorable for development, a tropical cyclone formation alert was issued on September 2. However, strong easterly shear separated the showers and thunderstorms from the center of circulation. Despite the shear, sufficient convection developed around the center; the National Hurricane Center (NHC) classified it a tropical depression at 0600 UTC, while centered about 390 miles (630 km) south of the southern tip of Baja California. The NHC initially did not recognize the system as a tropical depression and did not initiate advisories on it until several hours later. The depression quickly intensified into a tropical storm due to a brief relaxation of the wind shear and was given the name Karina while located about 25 mi (40 km) north of Socorro Island.

Karina was located to the south of a weakening mid-level ridge, leading to a relatively slow west-northwest movement at 9 mph (15 km/h). Upon becoming a tropical storm, Karina reached its peak with winds of 40 mph (65 km/h). There was uncertainty as to the intensity of the storm, as the Dvorak technique—a system used to estimate the intensity of a tropical cyclone—rendered an intensity of 50 mph (80 km/h); but because the center of the storm had just moved under the deep convection, the winds were held at minimal tropical storm intensity. That night, 12 hours after being declared a tropical storm, Karina was downgraded to a tropical depression. Strong easterly wind shear of at least 25 mph (40 km/h) tore away the deep convection that previously surrounded Karina. Karina was moving into a stable environment over cooling waters which would prevent convection from redeveloping, despite a forecast of lessening wind shear. The forward motion gradually decreased. By the morning of September 3, convection had been sheared 125 mi (200 km) from the center of circulation, leaving only a swirl of clouds. Karina degenerated into a remnant low-pressure area later that morning and the NHC issued their final advisory. The remnant low quickly dissipated that afternoon.