NOAA predicts somewhat subdued Atlantic hurricane season for 2014; developing El Nino to blame
The U.S. National Oceanic and Atmospheric Administration issued its 2014 Atlantic Hurricane Season Outlook today, and it's looking like it will be a somewhat quiet one compared to normal, with up to 13 named storms, between three and six of which will develop into hurricanes, and perhaps one or two of those reaching category 3 or higher (with wind speeds of 178 kilometres per hour or higher).
The average number of named storms seen during the Atlantic Hurricane Season is around 12, with roughly half of those becoming hurricanes and half again becoming major hurricanes. So, this puts the forecast for the 2014 season at near-normal to below-normal.
The main reason for this more subdued forecast, according to the experts, is the El Nino that appears to be developing in the equatorial Pacific Ocean. This weather pattern, which sees the Pacific trade winds diminish for months at a time, allowing warm waters near northeastern Australia to 'slosh back' towards northwestern South America, typically causes the opposite effect in the Atlantic trade winds. It's this increase in the Atlantic trade winds that's expected to give a more subdued season this year.
It may seem counter-intuitive that an increase in wind speed would hurt hurricane formation, given that they, themselves, are swirling vortexes of extremely powerful winds. However, the way a hurricane develops and strengthens depends on how efficiently it can move heat absorbed from the surface of the ocean into its upper layers.
If wind speeds at the bottom and top of the storm are roughly the same (the 'wind shear' is low), the cloud layers and the storm's eye are oriented almost vertically from ocean surface to the top of the troposphere, like they are in the video above. The heat can rise straight upward through the cloud layers, reaching the most area of the storm possible while the sinking air in the eye can flow straight back down to the water's surface. If the shear is high, the top layers of the storm are blown by stronger winds than those at the surface, and the storm gets tilted. This means that the rising heat doesn't reach as much of the storm, and it even cuts off the flow of sinking air in the eye a certain ways up, reducing the overall strength of the storm. Also, the stronger winds higher up stretch the storm out, and a wider storm is a weaker storm.
Last year, the initial forecast for the Atlantic hurricane season was calling for an active to extremely-active season, but things obviously didn't play out that way. There a total of 14 named storms, which was a little above average. However, only two developed into hurricanes, Humberto and Ingrid, in early to mid-September, and they were only Category 1 storms. Humberto simply kicked off just west of Africa and meandered through the eastern Atlantic before dying. Ingrid, on the other hand, made landfall in Mexico just a day after Hurricane Manuel hit from the Pacific side. The combined effects of both storms touched off flooding and landslides, claiming nearly 200 lives and causing 75 billion pesos in damages.
Why was there such a disparity between the initial forecast and what really happened last year? Although all the conditions were there at the start for a very active season to develop, according to a post-season analysis, the weather patterns pushed a lot of dry air over the Atlantic once the season started - from further north over the Central Atlantic, from over northern Africa, and from over northeastern South America. This dry air suppressed the whole cycle of hurricane formation, producing mostly weak storms.
Even though this season is forecast to be a fairly subdued one, at least compared to more active years (like 2010 and 2011), emergency management officials still advise everyone in areas that could be impacted by these storms to be ready.
"It only takes one hurricane or tropical storm making landfall to have disastrous impacts on our communities," Joe Nimmich, FEMA associate administrator for Response and Recovery, said in the NOAA press release.
In their effort to provide more information about the potential impacts of these storms, the U.S. National Hurricane Center is putting out some new tools for this year - including experimental maps to inform the public about potential storm surge flooding that may occur in their area. They also report an improvement in their Hurricane Weather Research and Forecasting model, which will allow them to give better estimates of the track and wind speeds of storms through their life-cycle.