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HURRICANE SEASON OUTLOOK 2012

It's that time of year again...
 
Hurricane Season runs from June 1st to November 30th, however we've already had the first named storm of the season, with Alberto early this week. Despite the early named storm, most signs are pointing to a "Normal" hurricane season... in terms of the actual number of named storms and hurricanes in the Atlantic.
 
"Normal" is based on the 1981-2010 average of 12 named storms, of which 6 become hurricanes, of which 3 become major hurricanes. (Category 3 or higher) 
 
The National Hurricane Center released their forecast today, which was fairly close to the also widely respected Colorado State University outlook and the Tropical Storm Risk forecast, from the University College London.

HurricanesMay242.JPG
MAIN FACTORS FOR 2012

Sea Surface Temperatures
 
The first main factor that hurricane experts are looking at, is the sea surface temperatures in the MDR (Main Development Region) of the Atlantic ocean. Last year, sea surface temperatures were running well above normal in the MDR and that helped to fuel a very active hurricane season. However currently, temperatures are average or even slightly below average in that critical zone between 10N and 25N.

SST20122.PNG

Note the warmer than normal sea surface temperatures in Atlantic Canada, all thanks to our warm Spring. If this warmer than normal ocean temp trend continues, it could be a factor in August or September. If a storm rolls up the coast later this Summer and over warmer than normal ocean temps, the storm could stay 'fueled' for longer. This is something the Canadian Hurricane Centre talked about in their briefing today.

NOAA's long range forecast model (below) shows warmer than normal temps continuing into the late Summer and early Fall for Atlantic Canada. The model is also bringing sea surface temperatures back to slightly above normal in the Main Development Region for tropical storms.

SST2012.PNGAs NOAA points out in their outlook,  hurricane activity is very sensitive to sea surface temps in the tropical Atlantic and really can make the difference between a slightly above, or slightly below normal season. They also point out that forecasting sea surface temps so far in advance is tough and there is "considerable uncertainty". 
 
Tropical Multi-Decadal Signal
 
The main contributing factor for our chance of a completely average or even slightly above average year, is the continuation of the 'Tropical Multi-Decadal Signal'. This is our current pattern, which includes an enhanced African monsoon, has been in place since the mid 1990's and is credited with increasing Atlantic hurricane activity.

AMO2012.PNG
Developing El Nino?
 
The main contributing factor that could keep this a below average year, is the possibility of a developing El Nino. El Nino of course, is the name for the warming pattern that occurs in the equatorial Pacific Ocean. El Nino is the second largest driver of the world's weather, next only to seasonal warming and cooling, so it's no surprise it also has an influence on hurricane season. In 'most' years, when an El Nino develops in the Pacific Ocean, there is less hurricane activity in the Atlantic. The warming of the Pacific in an El Nino event creates an atmospheric circulation pattern that brings strong upper-level winds over the hurricane development area in the Atlantic. Those winds create high wind shear conditions, which hinder tropical storm development by blowing the tops off of brewing storms. As of now, forecast models are currently split between predicting normal Pacific Ocean temps, or an El Nino setup this Summer. However, if an El Nino does develop, that would likely help to keep numbers lower than average, especially later in the season.  
 
ElNino.PNG
So where does all of this leave us? Well, it seems likely that we won't have a well above average year, like last year, or a well below average year. Depending on exactly how things shape up, chances are the number of storms will fall right in that "normal" range.
 
Of course, as we all know, it only takes 1 storm to roll up the Eastern Seaboard and into Atlantic Canada and cause a headache. So it's important to remember, even though the number isn't expected to reach the 19 named storms we had last year, we could easily see a few tropical visitors again this year.

Atlantic Canada Watch
 
As we move into the Summer season, we'll also start to get a better handle on the atmospheric pattern shaping up across North America and whether it favours those tropical storms to stay to the South and track into the Caribbean & Southern U.S... or whether they swing North and head up the Eastern Seaboard. A huge influence on this, is the semi permanent High pressure area near Bermuda (called the Bermuda-Azores High) and how strong it is. If that High is weaker than normal, it's typically easier for storms to curve North and head in our direction. This graphic courtesy of http://blog.chron.com does a great job of showing the importance of the Bermuda High. 

BermudaHigh.jpg
Hurricane Season here in Atlantic Canada, typically ramps up in August & September and subsides in October. 

Of course, I have only grazed the surface and given you the 'Coles notes' version, of what these great Meteorologists, Climatologists and Forecasters have been researching for months. If you would like to read their entire reports, the links are below!



 
Ryan

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