Storm & Security

SPECIAL / REPORT | by Howard Shingle | The Heat Is On Experts warn of above average to 'very active' remainder of 2013 hurricane season. The most active part of the Atlantic hurricane season is now—historically, August through October. As coastal communities and mitigation professionals prepare for increasing storm activity, updated forecasts emphasize the 2013 season is on track to be above normal. When NOAA issued its updated outlook in early August it noted the season is shaping up to be above normal with the possibility that it could become "very active." By mid-August, the season had already produced five named storms. "Our confidence for an above-normal season is still high because the predicted atmospheric and oceanic conditions that are favorable for storm development have materialized," said Gerry Bell, Ph.D., lead seasonal hurricane forecaster at NOAA's Climate Prediction Center, a division of the National Weather Service. "Also, two of the named storms to date formed in the deep tropical Atlantic, which historically is an indicator of an active season." The conditions that Bell speaks of include aboveaverage Atlantic sea surface temperatures and a stronger rainy season in West Africa, which produces wind patterns that help turn storm systems there into tropical storms and hurricanes. By early August, these conditions were similar to those that have produced many active Atlantic hurricane seasons since 1995, he added. On May 24, just before the start of the Atlantic hurricane season, most of the ocean energy available for hurricanes was confined to the northern Caribbean Sea, which is typical for that time of the year. The map shows that conditions prior to June were generally not conducive to tropical storms and hurricanes in much of the Atlantic basin. In contrast, the fiery orange hues in the map of August 4 show the hurricane-fueling warmth had expanded significantly, extending east across the Caribbean Sea and tropical Atlantic Ocean, north into the Gulf of Mexico, and even into the Gulf Stream Current just off the southeast coast of the United States. As the summer progressed, warm waters expanded far enough eastward into the Atlantic during June and July to help generate two named storms, Chantal and Dorian, in the deep tropical Atlantic. Named storms forming in this region as early as June and July historically indicate an active season. By August, all of these indications of an above-normal hurricane season—early summer storms generated in the deep tropical Atlantic, above-average Atlantic sea surface temperatures, and a strong rainy season in West Africa—remained. Turning Up the Heat One of the most important climate factors behind the expected active season is heat. These two maps presented here show the tropical cyclone heat potential of the tropical Atlantic Ocean ramping up between May 24 and August 4. This "hurricane heat potential" depends not just on the surface temperature, but also on the depth of the warm water. Yellow and orange colors indicate places where the amount of heat in the water column is enough to significantly impact the intensity of hurricanes, provided that atmospheric conditions are also favorable. Blue colors show where there was no hurricane heat potential; water temperatures were below 80°F—the minimum temperature needed to sustain hurricanes. May 24 August 4 PEOPLE IN THE KNOW 2013 / STORM & SECURITY PROTECTION 11

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