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May 25

The 2016 Atlantic Hurricane Season: How Will It Shape Up?

A week from today, commences the 2016 Atlantic Hurricane Season. In recent years, we’ve encountered historically low numbers in terms of named storms, hurricanes and major hurricanes across the Atlantic Basin and Gulf of Mexico as these regions have seen minimal tropical activity.  Early on, global model guidance has been hinting at the tale of a different story this year as they are suggesting an increase in tropical activity across these regions, with an increase in threat to US mainland impact as well. Guidance is pointing at numbers to be normal or even slightly above normal.

Seasonal forecasts are derived using an array of techniques, accounting for current weather patterns, ocean science, NWP (forecast modeling) and statistical analyses. This gives us a better understanding of how drivers, or weather patterns, can affect the development of tropical disturbances over a 6-month season. A lot must be taken into account as there are so many variables and factors that go into a 6-month period.

Since the start of 2016, one of the prime drivers behind global weather patterns had been an incredibly strong El Nino signal. This is marked by a warmer than average ocean temperatures across the equatorial Pacific. El Nino is called an “oscillation”, meaning this type of signal will dissipate and reemerge every few years, as it is cyclical in nature. As we journey into the early part of Summer, we are beginning to see the dissipation of the El Nino signal as water temperatures have begun to cool across the equatorial Pacific. This developing cold pool signals the commencement of a La Nina signal, the opposite phase of the cycle.

A La Nina signal, like an El Nino signal, has many effects on weather patterns across the globe, with pronounced effects across the Atlantic hurricane basin. The flow during a La Niña signal is supportive of weaker wind shear in the tropical Atlantic, due to weaker winds both aloft (higher in the atmosphere) and near the surface. This pattern encourages convergence, which produces rising air needed for tropical storm development. So in La Nina years we tend to see more active tropical seasons, as storms typically find a more favorable environment to develop and strengthen and become sustained. Over the last two years, dominated by a strong El Nino signal, we saw minimal activity across the Atlantic Basin and record activity across the Pacific Ocean, speaking truth to this pattern.

A second driver, and a major driver at that, are the ocean water temperatures across the North Atlantic. Like El Niño in the Pacific Ocean, Atlantic Ocean water temperatures have cycles which affect global weather patterns. One long-term cycle is known as the Atlantic Multi-decadal Oscillation (AMO). This signal moves very slowly, but we have been in a warm phase of the AMO for the last several decades. This has helped drive an increase in overall hurricane activity in the Atlantic over this time span. However current water temperature patterns in the North Atlantic are trending in the opposite direction as they are cooler than average. Whether this is just a temporary blip or signals a larger flip in the AMO cycle is not entirely known, but regardless this cold water will have impacts on the upcoming hurricane season.

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Though the North Atlantic may be colder than normal, there will still be abundant warm water in the tropics to fuel hurricanes this season. In particular the water in the Caribbean, the Gulf of Mexico, and near the Atlantic Coast of the US are forecast to be warmer than normal. This would raise the concern that storms, as they approach land, would more easily maintain their intensity or even strengthen before landfall.

The presence of warmer than average ocean waters near the US coast, along with weak shear, are the two main drivers behind what is likely to shape up to be an above-normal hurricane season over the next 6 months. One of the hindering factors we must account for as well is the colder water in the North Atlantic which should could stunt storm development across this region.

cdas-sflux_ssta_atl_1

The 2016 Atlantic Hurricane Season by the numbers…

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