Kevin Myatt is The Roanoke Times' weather columnist.

kevin.myatt
@roanoke.com
981-3341

Weather with Kevin Myatt

Recent columns

• Winter trying again to show up with snow
• We got graupel, but not on official record
• Moisture could get caught up in cold blast
• Column archive

Read the Weather Journal blog

• Many looking past mild, quiet week toward possibly wild weekend
• Sprinkles or flurries possible Tuesday, but maybe something bigger for the weekend?
• For now, it looks like a quiet, mostly mild week ahead for SW Virginia
• Weather Journal blog

#swvawx on Twitter

@KevinMyattWx

• Follow Kevin on Twitter at @KevinMyattWx

The Atlantic hurricane season officially begins Friday, and the experts are expecting it to be an active one.

Didn't we hear this same thing about a year ago?

Yep. Almost exactly.

Before the 2006 season, the National Hurricane Center forecast 13-16 named storms, eight to 10 hurricanes and four to six major hurricanes. The Colorado State University team of Philip Klotzbach and William Gray -- the latter of whom which pioneered this kind of seasonal hurricane forecasting in the 1980s -- called for 17 named storms, nine hurricanes and five major hurricanes.

Compare that to what's listed in the accompanying box for the 2007 hurricane forecast, and you'll see it's almost identical.

The 2006 season underperformed by a wide margin. There were 10 named storms, five hurricanes and two major hurricanes. Essentially, that is an average Atlantic hurricane season.

After a total of eight hurricanes made landfall in the United States in 2004 and 2005, not one hurricane came ashore in the U.S. in 2006.

The surprisingly sudden emergence of El Nino is most widely cited as the reason the 2006 hurricane season underperformed. El Nino, the periodic warming of a streak of central Pacific waters, causes increased storminess over the Pacific. In turn, this leads to stronger high-level winds that shred developing tropical systems over the Atlantic, resulting in a weaker hurricane season.

The collapse of that El Nino during the late winter is one of the major reasons both the National Hurricane Center and the Colorado State team are projecting the 2007 season to be active.

It is almost unheard of for an El Nino to regenerate within a few months after the last one diminished, so the thinking is that near-normal Pacific sea surface temperatures or even below-normal temperatures -- termed La Nina -- will allow for greater tropical development in the Atlantic.

Hurricane seasonal forecasting is far from perfect, because there are innumerable factors that go into tropical storm development. So it is typical that these forecasts are retooled as the season progresses. The forecasts were downgraded last year, though they never caught up with really ended up happening.

I issue two cautions in considering the upcoming hurricane season.

First, please don't make one hurricane season a referendum on global warming, pro or con.

When the 2004 and 2005 hurricane seasons were so extreme for the U.S., many people pointed to global warming as a chief factor. When 2006 was such a flop, some skeptics pointed to it as evidence that global warming wasn't such a big deal.

The study of the relationship between hurricanes and global temperature is meaningful only over periods of several decades or longer.

There is much ongoing research on the subject, taking into account not only the observed increase in worldwide average temperature widely believed to be linked to human production of carbon dioxide, but also known natural oscillations in the frequency of hurricanes.

The formation of hurricanes is extremely complex. A warming climate may produce warmer sea temperatures that would fuel stronger hurricanes and at the same time cause strong upper-level winds that would retard hurricane development.

In any event, this is only one hurricane season, so short-term factors can easily overcome and render meaningless any long-term trends over the course of a few months.

Second, it's not only about the U.S.

These forecasts are not saying that three to five major hurricanes will hit the United States, but rather, that three to five major hurricanes are expected to form in the North Atlantic basin, which includes the entire Atlantic Ocean north of the equator, the Gulf of Mexico and the Caribbean Sea.

It is possible that this could be a highly active season without any major hurricanes coming ashore in the U.S. -- though, obviously, the more hurricanes that form, the more likely it is that some of them will strike.

Islands in the Caribbean are even more at risk in an active hurricane season than the U.S.

It would take only one especially deadly hurricane to make the 2007 season memorable even if the numbers underperform forecasts.

On the flip side, an active season in which most of the hurricanes spun harmlessly out to sea would be easily forgotten.