Tropical Storm Barbara (2007) - Meteorological History

Meteorological History

A tropical wave moved off the coast of Africa on May 14, which is believed to have been the impetus to Barbara. The wave axis crossed Central America on May 25 and emerged into the eastern North Pacific Ocean the next day. Interacting with the Intertropical Convergence Zone, a broad surface low pressure area developed within the area on May 27, and as it drifted northward the system maintained limited and disorganized convection. On May 29, convection increased and became concentrated near the low pressure center, and banding features developed in its eastern semicircle as the circulation became better defined. It is estimated the system formed into Tropical Depression Two-E at 1800 UTC on May 29 about 115 miles (185 km) southeast of Puerto Escondido, Oaxaca. Upon becoming a tropical cyclone, the depression was stationary in an area with warm sea surface temperatures, very light wind shear, and favorable upper-level conditions.

In the hours after becoming a tropical cyclone, the deep convection associated with the depression decreased, though it again increased later in the day. A ragged rainband developed in the southeastern quadrant of the circulation, and based on increased Dvorak numbers and improved presentation on satellite imagery, the National Hurricane Center upgraded the depression to Tropical Storm Barbara on May 30 while it was located about 115 miles (185 km) south of Puerto Escondido. This marked only the third time on record that two storms formed in May in the basin, after 1956 and 1984. Initially, Barbara was forecast to intensify to attain hurricane status and reach winds of 85 mph (135 km/h).

The storm drifted southward and later eastward due to northerly flow behind a mid- to upper-level trough in the Gulf of Mexico. With well-defined outflow and warm sea surface temperatures, Barbara became better organized as tightly curved bands of convection developed near the center. However, by May 31, increased wind shear and less inflow deteriorated the definition of the circulation, causing the storm to weaken. By later that day, the system contained a very small circulation within a large-scale trough, and early on June 1 it was downgraded to tropical depression status. Later in the day, convective banding features re-developed, and after a QuikSCAT overpass indicated a well-defined circulation in the system, Barbara was again upgraded to tropical storm status. The storm reached peak winds of 50 mph (85 km/h) and turned to the northeast as it tracked through a break in a ridge extending from the southwest Gulf of Mexico. Banding features continued to organize, and shortly before moving ashore a low-level eye feature developed. At about 1300 UTC on June 2, Barbara made landfall just west of the border between Mexico and Guatemala. The center quickly deteriorated to tropical depression status over the mountainous terrain of extreme southeastern Chiapas, and Barbara dissipated within twelve hours of moving ashore.