To borrow and mangle a quote from Groundhog Day, "Well, it's hurricane season...again." Beginning June 1, anyone who lives along the Gulf of Mexico, Caribbean Sea or Atlantic Ocean starts to cast a wary eye on the tropics. As the temperatures warm up through summer, so does most of the Atlantic Basin, generating the energy necessary to produce tropical storms and hurricanes. But there are many factors that influence the development of those storms, which leads to unpredictability. Still, every year, forecasters trot out their preseason predictions.
Before getting too deep into those, it's important to note the factors that go into the development of hurricanes. If you live on the Gulf Coast, it is information worth knowing.
Hurricanes are formed when warm, moist air destabilizes the atmosphere and creates a small low-pressure area. This happens over the tropical waters of both the Atlantic and the Pacific. In the case of the Atlantic, that begins to occur in June and lasts until around October, though the season stretches out until December 1.
The primary factors influencing the development of storms include sea surface temperatures, upper level winds and wind shear, dry air, interaction with land and, believe it or not, Saharan dust.
In short, tropical storms need warm water below them and light winds as well as moist, unstable air above. The deeper the warm ocean temperatures go, the better. The more calm the winds, the better. The more unstable the air, the better. Storms also weaken over land, so any interference with land masses, particularly mountainous areas, can degrade or even dissipate storms. Finally, dust that blows off the coast of Africa from the Sahara Desert can block sunlight, cooling the air and preventing the development of storms.
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We also happen to be in the middle of a period of increased hurricane activity that began in 1995 referred to as the Atlantic Multi-decadal Oscillation (AMO). This is an atmospheric cycle that leads to increased hurricane activity. It lasts for 25-40 years or more, so we have a ways to go before that changes. The good news for 2014 is that predictions are calling for a below-average year for storms. The average number is around ten, but that increases to around 12 during the AMO. This year, most forecasts, including the most prominent from both the National Hurricane Center and Colorado State University, are calling for between eight and 12 named storms, with three to six becoming hurricanes and one or two major hurricanes (category three or above).
The main reasons cited for the low predictive numbers include below-average sea surface temperatures across the Atlantic and the presence of wind shear caused by what is turning into a fairly strong El Niño event.
El Niño is a weather phenomenon that results in concentrated heat in the eastern equatorial region of the Pacific Ocean. The increase in heat content in the ocean generates winds that blow east across Central America and across the Atlantic Basin. These winds tend to inhibit the growth of hurricanes. Most observers are predicting a particularly strong El Niño event that should sustain itself through the heart of the Atlantic hurricane season (August and September).
That doesn't mean there isn't cause for concern. It only takes one storm to have a devastating impact on the Houston area. Numerous hurricanes have struck the U.S. coastline during El Niño years, so it is important to be prepared. Fortunately, forecasts are calling for the most likely landfalls of storms this year to be from the mid Gulf Coast eastward, but no one will care about the forecasts if we are staring down a major hurricane in August, so it's a good time to start paying attention.