August 15th, 2012

Increased Storm Risk in West Atlantic and Gulf of Mexico

Posted at 1:00 AM ET

Increasingly unstable air, diminishing wind shear and water temperatures in excess of 27 degrees C will enable tropical cyclone development. The historical record shows a greater threat to land from storms originating in these areas.

From August through October, weather disturbances known as African Easterly Waves will leave the coast of Africa on a frequent basis. It is not unknown for these waves to remain intact as they cross the Atlantic, in a fairly weak state, developing into major hurricanes when they reach an enabling environment. Hurricane Andrew (1992) reminds us of this fact. Andrew was the first named storm in late August of 1992, during a very quiet season (7 named storms, 4 hurricanes, 1 major hurricane). The tragic and costly impacts of Andrew are well known.

The bottom line is that while tropical cyclone activity may be reduced, storms that develop in the West Atlantic and Gulf pose a higher threat to land, including the coastal United States and Canadian Maritimes.

We should not see a repeat of the 2004 or 2005 seasons in 2012. Conditions are simply not the same this year in the Atlantic. Yet 1992 reminds us that “it only takes one.” It is impossible to rule out the landfall of a major hurricane in the Atlantic basin for the 2012 season. As we enter the peak months, plans should remain in place to respond to the threat of a major hurricane for all areas of risk, including the Canadian Maritimes, Texas and all points in between.

Most sources, including the National Hurricane Center and Colorado State, have been predicting slightly below the ten year average of Atlantic tropical cyclone activity (and slightly above the long-term average). Prediction essentials include slow El-Niño onset and marginal ocean temperatures. The “much advertised” El-Niño onset in the Pacific has been slow, and its effects on suppressing Atlantic hurricane activity will be delayed. The effects will be further suppressed by the current phase of the Pacific Decadal Oscillation (another feature affecting hurricane activity). Atlantic sea-surface temperatures have been steadily increasing in recent weeks, and exceed 27 degrees C in the West Atlantic (particularly the Gulf of Mexico). Fortunately, Atlantic sea-surface temperatures are not excessively above 27oC, limiting available energy for tropical cyclone intensification.

The Season So Far

The early months of the 2012 season saw four named storms. Two formed in May, marking the first time this has happened since 1908.

June marked the earliest date on record for the occurrence of four named storms in the Atlantic basin. The weeks following June saw a period of welcome quiet, with no named storms and very little tropical activity.

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