But the season normally is most active from August through October, which is why the National Oceanic and Atmospheric Administration offers a midseason update each year.

In May, Dr. Bell and his team forecast an above-normal season, with 11 to 17 named storms and as many as four major hurricanes. In a typical year, the Atlantic will have 12 named storms and three major hurricanes. The 2010 season was exceptional, with 12 hurricanes, including five major ones, among 19 storms.

Dr. Bell said that as the season has progressed, the forecast has become more confident, with a 60 percent likelihood that the season will be above normal, compared with 45 percent in May. The likelihood of a below-average season is now only 10 percent, down from 20 percent.

Dr. Bell said conditions that were predicted before the season have developed and are likely to persist. Those include warmer-than-average ocean temperatures, which add energy to storms, and weaker-than-average trade winds and wind shear. Adding to the confidence is that there is even less likelihood that El Niño will develop. El Niño can result in wind shear, which disrupts storms as they develop.