Friday, August 10, 2012

Tropical Storm Helene (2012)

Storm Active: August 9-11, 17-18

On August 5, a tropical wave and associated low pressure system moved off of Africa. It exhibited small areas of thunderstorm activity and increased in organization over the following days as it moved west over the tropical Atlantic.

During the afternoon of August 9, convection became concentrated at the center of the system, and it became Tropical Depression Seven. From its genesis, the system interacted with dry air, and this inhibited development of shower activity north of the center later that day and into August 10. The persistent ridge over the north Atlantic caused Seven to track westward rapidly.

By August 11, the system was moving so rapidly that an organized center of circulation no longer existed in conjunction with the system. It was thus downgraded to a tropical wave. The wave continued to move into the Caribbean, producing some heavy rain around the Windward Islands. Convection increased as the wave approached central America, but land prevented redevelopment.

By August 14, the remnants of Seven had moved over land, but the system took a turn to the northwest, ultimately allowing it to emerge into the Bay of Campeche on August 16. Convection increased in association with the system, and a center of circulation became defined on August 17, causing the system to be upgraded to Tropical Storm Helene, already at its peak intensity of 45 mph winds and a minimum pressure of 1004 mb.

The system moved northwest towards the coast of Mexico, and weakened upon interaction with land. Convection remained scant, and the center was hard to identify on satellite imagery during the morning of August 18. The cyclone made landfall during the late morning hours in Mexico, bringing heavy rainfall to some inland areas.

The cyclone weakened to a tropical depression that evening, and dissipated completely late that night, its circulation destroyed by the mountains of Mexico. Overall, the impact of the system was heavy rain, particularly in Trinidad and Tobago (as a tropical wave), and the coast of the Bay of Campeche.

Helene at peak intensity after reforming in the Bay of Campeche.

Track of Helene, including its path through the Caribbean as a non-tropical system (non-tropical points indicated by triangles).

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