In like a lamb, out like a lamb

With the epic destruction wrought by Hurricane Katrina in 2005, US residents were preparing for the seemingly inevitable encore in 2006. Thankfully, it never came. With just 9 named storms and 5 hurricanes (below the seasonal average), Hurricane Season 2006 failed to live up to lofty expectations. One popular theory for the decline is the unexpected early onset of an El Nino event. The concept of "El Nino" sometimes leads to confusion among casual weather observers. After all, El Nino is associated with warming ocean temperatures. And we know that warmer water can provide more fuel for developing tropical systems. So why does El Nino often decrease the likelihood of East Coast storms? You must remember that a pronounced El Nino event can alter the pattern of wind/air flow near the tropics, increasing what is commonly referred to as "wind shear". This wind shear can tear (or "shear") apart developing hurricanes. In fact, there have been many examples of El Nino patterns coinciding with fluctuations in tropical activity. The early '90s saw increased frequency of "El Nino" events. The early '90s was also a quiet period for tropical activity in the Carolinas. Of course, there are many parameters other than El Nino that play a role in seasonal forecasting. Researchers at North Carolina State University constructed their own forecast this year, based heavily on sea surface temperature variation (from normal) in the Northern Atlantic and Southern Atlantic. Interestingly, the NCSU forecast was quite accurate. The team "officially" forecast 5-6 hurricanes for 2006. In reality, 5 formed, including "Ernesto" (a storm that caused problems in southeastern NC). Dr. Lian Xie, once a professor of mine, is a tropical forecaster with NCSU. Ironically, I was listening to one of his lectures back in 1996 as three storms were being tracked in the open Atlantic -- Edouard, Fran, and Gustav. I remember Dr. Xie predicting that Fran, not Edouard or Gustav, would be the storm that affected North Carolina (and we all know the true extent of Fran's impact). In fact, 1996 would go on to become one of the most costly years of tropical activity in the Carolinas- a far cry from our most recent "weak" season.