2017 Atlantic Hurricane Season begins: What you need to know

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Monday, June 5, 2017, 1:47 PM - The 2017 Atlantic Hurricane Season is now underway, and forecasters are monitoring the potential for a more active than normal season ahead. An oncoming weak El Nino event in the equatorial Pacific may play a role in determining the overall number of storms, but factors closer to home will increase the risk for intense storms to threaten the North American coast this year.

The hurricane season officially runs from June 1 to November 30 – though this year got off to an early start when Tropical Storm Arlene formed in April. In a typical year, the frequency of storms begins to ramp up in late summer, reaching a peak around September 10. The number of storms decreases through the fall as Atlantic water temperatures cool, although a secondary peak does occur in October as lingering warm water near the North American coast provide a favorable environment for “home grown” systems.

An average Atlantic Hurricane Season produces 12 named storms, six of which go on to become hurricanes, reaching a wind speed of 119 km/h or greater. On average three of those become major hurricanes with winds of 178 km/h or greater.

The Climate Prediction Center – the long-term forecasting branch of the National Oceanic and Atmospheric Administration (NOAA) – released their official forecast for the season on May 25, predicting an above normal number of storms in 2017.

The NOAA forecast predicts 11-17 named storms this year, with 5-9 hurricanes and 2-4 major hurricanes.

The Colorado State University Tropical Meteorology Project team released an updated outlook for the 2017 hurricane season on June 1, which forecasts an above normal number of named storms (14), and a near normal number of hurricanes (6) with the potential for 2 major hurricanes. This is an increase from their most recent outlook in April, which forecast 11 named storms and 4 hurricanes.

But keep in mind that hurricane seasons are not all about the numbers. For example 1992 produced only 7 named storms, but among them was Hurricane Andrew – one of the strongest and costliest storms ever to affect the United States. So rather than focusing on the overall number of storms, it’s important to also consider the drivers than can affect the intensity of storms, or increase the chances of an impactful landfall.

The main factors that affect the number and strength of hurricanes in a season are wind shear and water temperature. This year is expected to see near to below normal amounts of wind shear in the Atlantic basin, which provides favorable conditions for storms to form. Although typically we associate oncoming El Nino events with strong wind shear – and thus fewer hurricanes – this year’s event is expected to be relatively weak, and so its effects are likely to be overwhelmed by other drivers.

There are also some preliminary indications that the dominant jet stream pattern over North America during the late summer and early fall will be one that heightens the threat for tropical cyclones to make landfall.

In addition, the ocean water temperature pattern increases the concern for impactful landfalls in 2017. Temperatures in the main development region of the Atlantic basin are near to above normal, providing ample fuel for storms to intensify. And perhaps more importantly, temperatures near the North American coast are above normal as well, which increases the potential for storms to form nearer to land – reducing the opportunities for them to recurve harmlessly out to sea.

Warmer than normal water just offshore also increases the threat for storms to maintain their intensity or even strengthen as they approach the coast.

Other variables also come into play, such as the amount of dry air over the Atlantic and the presence of Saharan dust. But all things taken into account, it appears that 2017 is likely to produce an active and potentially memorable hurricane season.