Tropical Storm Hermine (1998) - Meteorological History

Meteorological History

On September 5, 1998, a tropical wave emerged from the west coast of Africa and entered the Atlantic Ocean. The wave was not associated with any thunderstorm activity until it reached the Windward Islands, when cloud and shower activity began to increase. Continuing westward, the disturbance approached the South American coastline and turned into the northwest Caribbean Sea. The wave interacted with an upper-level low-pressure system and another tropical wave that entered the region. At the time, a large monsoon-type flow prevailed over Central America, part of the Caribbean Sea, and the Gulf of Mexico. An area of low pressure developed over the northwestern Caribbean, and at about 1200 UTC on September 17, the system was sufficiently organized to be declared a tropical depression in the central Gulf of Mexico.

Initially, the cloud pattern associated with the system featured a tight and well-defined circulation, as well as clusters of deep convection south of the center. Due to the proximity of a large upper-level low-pressure area in the southern Gulf of Mexico, the surrounding environment did not favor intensification. Influenced by the low, the depression moved southward. The system completed a cyclonic loop in the central gulf, and by early on September 18 was drifting northward. As a result of wind shear, the center of circulation was separated from the deep convective activity. Early the next day, deep convection persisted in a small area northeast of the center. Forward motion was nearly stationary, with a gradual drift east-southeastward. Despite the wind shear, the depression attained tropical storm status at 1200 UTC; as such, it was named Hermine by the National Hurricane Center.

Shortly after being upgraded to a tropical storm, Hermine reached its peak intensity with maximum sustained winds of 45 mph (75 km/h). The tropical storm-force winds were confined to the eastern semicircle of the cyclone. Hermine tracked northward and approached the coast, where it nearly stalled. A continually weakening storm, it moved ashore near Cocodrie, Louisiana at 0500 UTC on September 20 with winds of 40 miles per hour (64 km/h), and then deteriorated into a tropical depression. On its landfall, associated rain bands were deemed "not very impressive", although there was a rapid increase in thunderstorm activity east of the center. The thunderstorms produced heavy rainfall in parts of southeastern Louisiana and southern Mississippi. The storm progressively weakened as the circulation moved northeastward, and dissipated at 1800 UTC. Initially, it was believed that Hermine's remnants contributed to the development of Hurricane Karl; however, this belief was not confirmed.