Hurricane Prediction for 2006 is Above Normal Compared to the Long-term Average

Hurricanes need both warm sea surface temperatures and calm winds to develop. Warm water provides both heat and humidity needed for storm formation. Strong winds would tear a developing storm apart, while calm winds allow a hurricane to build. At the beginning of the season, June 1, sea surface temperatures were warmer than normal, and winds were calm.

Even so, this is not quite as hurricane-friendly as last year when sea surface temperatures were 2 degrees warmer than they are at the opening of the 2006 season. The warm temperatures in 2005 allowed a record seven storms to form by the end of July, one of which, Hurricane Emily shown in pic, set records when it became the first category 5 hurricane to occur in July. All other Atlantic storms of that strength have developed later in the season.

In June of this year, the National Hurricane Center predicted a very active hurricane season with 13 to 16 named storms, 4 to 6 of which could become major hurricanes. However, earlier this month, forecasters at the National Oceanic and Atmospheric Administration (NOAA) revised downward slightly their early-season predictions of the 2006 Atlantic hurricane season. Citing atmospheric and oceanic conditions less conducive to hurricane formation than they initially expected and the fact that the transition away from La Niña-like rainfall patterns occurred more quickly than expected, the National Hurricane Center decreased its predictions of named storms (12-15 instead of 13-16), hurricanes (7-9 instead of 8-10), and major hurricanes (3-4 instead of 4-6). The revised prediction is still above-normal compared to the long-term average.

The satellite images to the right show sea surface temperatures hurricane-ready, warmer than 28 degrees celsius. You can see from the images that the expanse of hurricane-ready water between Africa and the Gulf of Mexico grew over the two-week period. The color of the Gulf of Mexico became a deeper red, as well; any storms steered into the region would find ample warm water to keep them going. According to NOAA, although sea surface temperatures in the tropical Atlantic did not warm as much as originally forecasted, they are nevertheless still above long-term average conditions, which will likely contribute to above-average hurricane activity from August-October.

Among the other factors that NOAA expects to contribute to hurricane activity over the remainder of the 2006 season is a hurricane-favorable configuration of the African easterly jet, a strong easterly wind in the middle levels of the atmosphere over West Africa. Waves of turbulence spin off this jet and head westward over the Atlantic; some of these easterly waves spawn hurricanes. Hurricanes that arise from African easterly waves are sometimes called “Cape Verde storms.”

Hurricanes that form in the Atlantic tend to circle the Bermuda High, a semi-permanent high-pressure system that sits over the Central Atlantic. In 2004 and 2005, the Bermuda High expanded to the south and west, pushing storms into the Gulf of Mexico and Florida. But as of May 31, 2006, the Bermuda High remained small and in a position that would steer storms up the East Coast of the United States or out into the Atlantic.

Why do surfers care about hurricanes?

...because hurricanes are capable of producing large waves of a good period (13-14 secs) if a variety of conditions are right. In general this means that the storm needs to be headed right towards you, with maximum winds over a multi-day period. Unlike winter storms the Fetch area is normally small, with winds greater than 30 knots rarely extending out more than 250 miles from the center of circulation, the 'eye'. But if the storm is headed right at you with a constant heading over several days, it is possible to develop a good amount of 'virtual' fetch, effectively increasing the fetch area and improving the chances for a longer period swell (14-17 secs). Bit of a dicey situation!

All well and good if you live in the Tropics I hear you say, but actually tropical storms produce swells in the north too. Normally hurricanes in the northern hemisphere track around the edges of large summer high pressure systems that develop in the central Atlantic, aka the Bermuda High I mentioned earlier. In the north Atlantic, as tropical storms approach the western most point of these oceans, if they don’t hit land or die out, they turn towards the north.

This year the Bermuda High is small and in a position to steer the storms north, rather than towards the land in the Gulf of Mexico or Florida. So, as the storms progress northward, and eventually northeastward, they loose their tropical characteristics. They move over colder waters off the north Atlantic and transform from being warm core to cold core, and turn extra-tropical. Extra-tropical systems generally will increase in size and fetch area, though winds will back off a bit. Regardless, they can in-turn take tracks towards Europe or Canada, producing nearly winter like storm surf in the early fall. Let's hope they come our way - bring on those September sessions!

Info and pics taken from http://earthobservatory.nasa.gov
More info on hurricanes and surf at http://www.stormsurf.com/page2/tutorials/hurricane.shtml