How does El Nino affect climate in the West?
Winter versus summer The most unambiguous signal is seen in the winter half-year, typically from October through March or April. A weaker signal may be seen in some parts of the West in summer or early autumn. Most of this discussion concentrates on winter. Tropical storms Eastern Pacific autumn tropical storms, west of Mexico, appear to be less frequent in El Nino years, a tendency which is well established in the Atlantic. However, those tropical storms that do occur have a greater than usual tendency to recurve into Mexico or the southwest U.S. Higher than usual water temperatures off the Mexican coast in El Nino years can help maintain their strength, or cause them to be stronger than they would otherwise be. Hurricanes need water temperatures of about 27 C (81 F) or more to sustain themselves. Winter circulation During El Nino years, the storm track more frequently splits into two preferred branches. The Aleutian Low, in the Gulf of Alaska, is deeper than usual, and one branch of
