The La Nina climate pattern is strengthening, increasing the chance that an active Atlantic hurricane season could intensify. The update Thursday from the U.S. National Oceanographic and Atmospheric Administration (NOAA) come as residents of Texas are cleaning up from the heavy rains of Tropical Storm Hermine, and as Tropical Storm Igor is moving across the Atlantic Ocean. The La Nina climate phenomenon is marked by a cooling of the tropical Pacific Ocean and was reported to be developing a month ago. It cooled throughout August and appears likely to last at least through early 2011, NOAA said. "La Nina can contribute to increased Atlantic hurricane activity by decreasing the vertical wind shear over the Caribbean Sea and tropical Atlantic Ocean," NOAA said. Wind shear is a sharp difference in wind speed at different altitudes in the atmosphere. A strong wind shear reduces hurricanes by breaking up their ability to rise into the air, while less shear means they can climb and strengthen. La Nina's cooling of the tropical Pacific is the opposite phase of the El Nino event, which is marked by unusually warm tropical water in that region. Each can happen every few years, usually with neutral conditions in between. Both climate patterns can impact worldwide weather by changing the direction and strength of winds and altering air-pressure and rainfall patterns.
