Although it hedged its bets by using a wide range, the US National Oceanic and Atmospheric Administration Climate Prediction Center on Thursday forecast a busier than average 2010 Atlantic hurricane season.

The range of 14 to 23 named storms and 8 to 14 hurricanes represents above average activity even at the low end of the forecast range. 

“The 2010 Atlantic hurricane season outlook primarily reflects an expected set of conditions during peak months – August through October – of the season that is very conducive to increased Atlantic hurricane activity,” the outlook report stated.

If the hurricane season produces anywhere near the upper end of the range, coastal areas in the Atlantic basin could be in for a rough year.

“If this outlook holds true, this season could be one of the more active on record,” said Jane Lubchenco, under-secretary of commerce for oceans and atmosphere and NOAA administrator. “The greater likelihood of storms brings an increased risk of a landfall. In short, we urge everyone to be prepared.”

The low end of the range is very similar to the 7 April numbers issued from noted Colorado State University hurricane forecasters William Gray and Phil Klotzbach, who predicted 15 named storms and eight hurricanes.  Those numbers are expected to increase when the duo release an updated forecast next Wednesday.

“The numbers are going to go up quite high,” Mr. Gray said Wednesday. “This looks like a hell of a year.”

The Climate Prediction Center also forecast three to seven major hurricanes of Category 3 or higher, which means with sustained wind speeds of 111 miles per hour or above.  The 2005 hurricane season featured seven major hurricanes, a record four of which reached Category 5 strength with sustained winds of at least 156 mph.

Reasons

Part of the reason for the increasingly gloomy forecast is the sudden collapse of El Niño, which is an anomalous warming of sea surface temperatures in the equatorial Pacific Ocean. The phenomenon causes upper atmospheric wind shear in the Atlantic Basin, something that hinders hurricane formation and strengthening.  Last year’s mild hurricane season was largely attributed to El Niño. 

Although El Niño has been forecast to subside this year, it was not supposed to happen until late this summer, and then only transition into what is known as an El Niño neutral condition.  However, over the past couple of months, El Niño has faded quickly and is already transitioning into a neutral state.  Forecast models are increasingly predicting it will transition all the way into a La Niña state by the time the peak part of the Atlantic hurricane season arrives in mid-August. The Climate Prediction Center pointed out that La Niña contributes to reduced vertical shear over the western tropical Atlantic.  But even if the El Niño/Southern Oscillation neutral condition remains, the lack of inhibiting factors from El Niño can produce a very active Atlantic hurricane season when other conditions known to promote tropical cyclone formation are present.  

The record-breaking 2005 hurricane season, in which there were 28 storms and 15 hurricanes, had an El Niño that quickly collapsed and gave way to an El Niño/Southern Oscillation neutral condition during the hurricane season.

In addition to the collapse of El Niño, NOAA cited record-high sea surface temperatures in the area of the Atlantic Ocean where most tropical cyclones form, known as the Main Development Region.  Not only are the sea surface temperatures in the region at record highs now, they were also at record highs in March and April.  One of the causes of the higher sea surface temperatures is a pronounced weakening of north-easterly trade winds, a pattern which is generally expected to continue through the hurricane season.

A third factor cited by NOAA to support its busy hurricane season forecast was the continuation of a multi-decadal period of high activity in the Atlantic Basin. This period, which began in 1995, is expected to continue this year.

Chances

The Climate Prediction Center also forecast the hurricane season in terms of percentage chances. The outlook calls for an 85 per cent chance of a above-normal hurricane season in terms of activity, with a 10 per cent chance of a nearly normal season, and only a 5 per cent chance of a below normal season.

With respect to Accumulated Cyclone Energy, an index which accounts for intensity and duration of named storms and hurricanes, the outlook forecast a 70 per cent chance that the 2010 season would range between 155 per cent and 270 per cent of the median.  Any value above 175 per cent is considered and extremely active, or hyperactive, hurricane season.