October 1998 Central Texas Floods - Meteorological History

Meteorological History

On September 25, 1998 a tropical wave emerged off the coast of Africa, producing intermittent concentrated clusters of convective activity. The wave traversed the Atlantic Ocean and the Caribbean Sea before crossing Central America on October 5 or October 6. After several days, convection increased, and Dvorak classifications initiated. Satellite imagery indicated that the system dissipated on October 11, although an area of cloudiness persisted off the coast of Mexico. After four days, the system regenerated and under diffluent flow aloft, deep convection became more concentrated; it is estimated that a tropical depression formed at 0000 UTC on October 16, about 230 mi (370 km) west-southwest of Manzanillo, Mexico. Initially, due to disorganization, determining the forward movement of depression was difficult, although a few hours later it was estimated that the system was tracking to the north-northwest. With favorable conditions aloft, the deep convection became more concentrated, and 12 hours after first developing, the depression intensified into Tropical Storm Madeline about 170 miles (270 km) southwest of Cabo Corrientes.

During the afternoon, convective cloud tops warmed slightly although the storm continued to intensify. Soon after, thunderstorm activity became limited as Madeline remained generally stationary in movement. An approaching mid-level trough turned Madeline to the northeast. Banding features gradually improved in organization, and late on October 17 the storm attained hurricane status. However, satellite imagery indicated that convective activity was confined to the western portion of the storm, and at the same time an eye began to form. Early on October 18, data from a Reconnaissance aircraft flight into the storm found a minimum central pressure of 985 mbar (29.1 inHg), as the storm was drifting to the northeast at around 4 mph (6.4 km/h) near the western edge of a large-scale east–west ridge axis. The apparent eye became cloud-filled shortly thereafter, and a slight increase in temperature was discovered near the center. Despite this, upper-level outflow was favorable, leading to predictions of slight intensification.

Shortly thereafter, Madeline attained peak winds of 85 mph (140 km/h) about 95 miles (150 km) southwest of San Blas, Nayarit. The hurricane maintained peak winds for about 18 hours while curving again to the northwest. With evidence of southern wind shear, only a small area of deep thunderstorm activity existed on October 19, and the system began to appear ill-defined of satellite imagery. The hurricane quickly weakened into a tropical storm, and by later that day, the storm became void of convection due to strong wind shear. On October 19, the storm was downgraded to a tropical depression, leaving just a swirl of low clouds midway between the southern tip of Baja California and mainland Mexico. By 0600 UTC on October 20, the remnants of Madeline had completely dissipated.