Atlantic hurricane season comes to a close

2015 turned out to be quite active despite a strong El Nino.

It is somewhat of a paradox that a strong El Nino, which we are now experiencing, tends to quell hurricane activity in the Atlantic Basin.

An El Nino, causes a warming of the surface waters of the Pacific Ocean. These warmer waters are the source area for typhoons. The warmer the waters, the greater the number and strength of these storms.

It is often reported that El Nino has a knock-on effect around the globe. One might suppose that some of those effects would be to increase the storm frequency in the Atlantic.

Yet an El Nino seems to have a dampening effect on Atlantic hurricanes.

This is primarily because it affects the behavior of winds through the atmosphere. Wind shear – the change of wind speed and direction with height – tends to increase, and this inhibits and disrupts hurricane formation. At least, that’s the theory.

In fact, the 2015 hurricane season, which runs from May 1 to November 30, turned out to be an almost ‘average’ season, albeit a somewhat contradictory one.

There were 11 named storms, four hurricanes and two major (Category 3, or above, on the five point Saffir-Simpson scale) hurricanes. This compares with the 1981-2010 average of 11.5 named storms, 6.1 hurricanes, and 2.6 major hurricanes.

As predicted, wind shear was strong throughout the season, but it did not extend as far east as usual.

The surface water temperatures of the eastern Atlantic, off the coast of West Africa, were near record-breaking levels. Consequently, much of storm activity began in the eastern or central part of the Basin.

Three storms were of particular note. The first was Hurricane Joaquin. Accumulated cyclone energy (ACE) is a measure of the total destructive power of a hurricane season.

Joaquin accounted for almost half of the season’s entire ACE, which, itself, was just 60 percent of the long-term average.

Joaquin was also memorable for being the strongest Atlantic hurricane since 2007, and it killed 35 people, and caused $100 million worth of damage across the Central Bahamas.

The deadliest storm of the season was Tropical Storm Erika, which hit the island of Dominica on August 27. 36 people died on the island and damage across the eastern Caribbean was estimated at $600 million.

The third noteworthy storm was Hurricane Fred. This was the first hurricane to hit the Cape Verde islands, off the coast of West Africa, since 1892.

It is also worth noting that, despite some record-breaking ocean temperatures in the Caribbean, no storms formed in the region.

No major hurricanes made landfall in the US for an unprecedented 10th consecutive season.

With the current El Nino expected to weaken in spring 2016, it is likely that next year’s season will see a return to “normal” activity.

Source: Al Jazeera


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