From the Christian Science Monitor (Pete Spotts) via Alaska Dispatch:
Over the past two hurricane seasons, La Niña has held sway – characterized by cooler than normal sea-surface temperatures in the eastern tropical Pacific and warmer than normal temperatures in the western tropical Pacific. These conditions flip-flop under El Niño. Each phase of this cycle alters wind patterns in ways that inhibit tropical-cyclone formation in the Atlantic during an El Niño and favor cyclone formation during a La Niña.
La Niña fizzled in April, leaving current conditions in a neutral phase some forecasters whimsically refer to as La Nada. Some models are forecasting the development of a weak El Niño between July and August, but for now it’s unclear whether it would last much beyond that.
Indeed, the season’s two early storms in May, Alberto and Beryl, highlight the influence wind conditions have. Both strengthened to tropical-storm levels over warm Gulf Stream waters off the coasts of Florida and the Carolinas. But they did so because the system of cloudiness they grew from traveled into a gap between two high-altitude rivers of air flowing west to east – the polar and subtropical jet streams, Dr. Masters explains on his Weather Underground blog.