Just before the start of the 2013 Atlantic hurricane season, U.S. forecasters were calling for an 'active to extremely active' season. Now, with just over a month left until the season is over, it's starting to look like the the season is a dud and the forecast is a bust.
The initial forecast was for something similar to the 2010 hurricane season, with between 13 and 20 'named' storms, 7 to 11 hurricanes and 3 to 5 major hurricanes. So far, the season hasn't even lived up to the minimum of that prediction, only producing a dozen 'named' storms and two hurricanes — Humberto in the eastern Atlantic in early September and Ingrid in the Gulf of Mexico in mid-September.
The last year that saw numbers that low was the 'below-average' 2009 hurricane season. There's still over five weeks left to go before it officially ends on November 30th, and we could see more storms before then. However, there would have to be a major and unprecedented outbreak of hurricanes to make up the difference between what was forecast and what actually happened.
So, why was this year's forecast so off compared to recent years? The factors for a strong season were certainly there, with warmer-than-normal ocean waters in the Atlantic and light trade winds. Also, El Niño, which is notorious for tramping down a hurricane season, wasn't active in the south Pacific, so we should have seen a lot of activity. However, according to Andrew Freeman, of Climate Central, three factors came into play after the start of the season that made it very hard for hurricanes to form.
The first was a pattern of sinking air across the Atlantic, which cut down on the amount of rising air that was available to develop into storms. The second was repeated shots of dry, dust-filled air from over the Sahara Desert. It's normally these winds from over the desert that push the storms across the Atlantic, but combined with the sinking air, it just served to suppress storms even further. Third, the differences in wind speed and direction between the ocean surface and the air high up was greater than usual, and this was basically tearing storms apart before they could form. Factors like these aren't easy to predict, though.
According to Freeman, they don't go into the forecast models right now, but researchers are looking into whether they can be predicted for future forecasts.
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One fear is that this 'busted' forecast will hurt the credibility of future forecasts. Even though weather forecasts are usually right, they're rarely remembered for being right. It's the relatively few incorrect ones that stick in peoples' minds. With this season performing so far below the predicted levels, it may lead some (or perhaps many) to reject the forecasts in years to come, even though they actually improve with greater computing power and more data being included.
One positive thing to take away from this season, so far at least, is that it has had relatively little impact on people's lives. Lives have been lost and damage has occurred, but nowhere close to what happened in 2010. There's still over a month to go in the season, and nature rarely holds to our schedules, so more storms could form, even into December. However, hopefully the season will just end quietly, we can count ourselves lucky, and move on to improving forecasts for the years to come.
(Image courtesy: NOAA/NASA)
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