GENEVA, Sept. 25 (Xinhua) -- A weak El Nino may develop in September and October and last into the northern hemisphere winter, the World Meteorological Organization said in its latest update on Tuesday.
During July and August, the tropical Pacific sea surface temperature increased and exceeded weak El Nino thresholds, but atmospheric characteristics of El Nino, such as sea level pressure, trade winds and cloudiness, have not yet developed, according to the update.
Therefore, the ocean-atmosphere system as a whole is considered to be currently in a neutral state but is "more likely than not" to respond in due course in a manner consistent with an El Nino, it said.
It also said continuation of neutral conditions could not be ruled out.
WMO pointed out that El Nino and La Nina are not the only factors that drive global climate patterns. Conditions in the tropical Indian and Atlantic oceans, for instance, also have an important influence on surrounding continental climate patterns.
The El Nino phenomenon is due to large-scale interactions between the ocean and the atmosphere. It is characterized by unusually warm ocean surface temperature in the central and eastern tropical Pacific, in contrast to the unusually cool ocean surface temperature witnessed in the same region during La Nina events.
Both El Nino and La Nina have a large influence on weather and climate around the globe.