Hurricanes Tracking Hurricanes

Hurricanes Tracking Hurricanes

Every few years, two or three successive hurricanes will follow similar paths, making similar landfalls. Why do these storms seem to follow paths of previous hurricanes?

In 1999, three hurricanes struck the North Carolina coastal plain with similar paths of devastation, the last one was Floyd, the worst of the three. In 2004, Florida was battered by four hurricanes, three of which hit the Florida peninsula with similar landfalls and trajectories. Hurricane Jeanne hit on September 24, 2004, arguably was the most devastating of the three.

Steering currents force hurricanes to follow similar paths. These steering currents may include the subtropical jet stream and high-pressure cells. A particular influence is the Bermuda high-pressure cell, found in the summer and early fall over the Atlantic Ocean east of the Carolinas.

Many hurricanes that threaten the U.S. east coast originate as clusters of thunderstorms over West Africa. Over the ocean these features slowly change into low-pressure cells circulating counterclockwise as they move westward in the Trade Winds. About half way across the Atlantic, they begin to move over warmer water and soon become tropical storms. Once they approach the Caribbean islands or enter the Caribbean or Gulf, they begin to “feed” on the very warm tropical waters. At this point they can become full-fledged hurricanes with sustained winds of 74 mph or more. Generally, once hurricanes threaten the U.S. Gulf or Atlantic coastline, they bear off? to the north and east.

As a rule of thumb, high-pressure cells, which rotate clockwise in the Northern Hemisphere, block the movements of hurricanes, forcing them to follow paths that skirt around the highs. The Bermuda high tends to block hurricanes from moving directly northward, forcing the storms to follow the western perimeter of the high-pressure cell. This path tends to be along the east coast of the United States.

Winds associated with cold fronts can also assume the role of steering currents. During the fall of the year, cold fronts backed by cooler Canadian air can invade the eastern United States. When these fronts swing across the eastern United States from northwest to southeast, they may further divert a hurricane to the northeast and east.

Finally, a more southerly route of the west-to-east flowing subtropical jet stream can divert hurricanes quickly off to the east.

Of the three primary steering currents, the Bermuda high is perhaps the most influential in causing hurricanes to take similar tracks along the east coast. As hurricanes skirt around the western side of the Bermuda high, the storms tend to follow the same general paths, particularly if the Bermuda high is strong and stable.

Likewise, three of the four Florida hurricanes followed somewhat similar tracks through the Florida peninsula, but all four were strongly influenced by the Bermuda high. Hurricanes Charley, Francis and Jeanne tracked northward across the peninsula, while Ivan took a somewhat different track.Examples of the North Carolina hurricanes were Dennis, Floyd and Irene in succession between September 5, 1999, and October 18, 1999. The Bermuda high shoved all three hurricanes westward from the Atlantic Ocean into the eastern coastal plain.

Erratic Hurricane Ivan, which entered the Gulf of Mexico and made landfall just east of Mobile Bay, then became a tropical storm that skirted all the way around a high-pressure center over the southeastern United States. In a most unorthodox geographic pattern, as a tropical storm, it moved southward between that high and the Bermuda high, crossed the Florida peninsula once more, crossed the Gulf of Mexico and made landfall in Texas. Such an unusual hurricane/tropical storm track has happened only a few times in recorded history.

Hurricanes and tropical storms that follow tracks of previous storms are generally explained by larger patterns of high pressure and the jet stream. Just as lightning can strike more than once in the same place, so too can hurricanes.

Leave a Reply

Your email address will not be published. Required fields are marked *