Synopsis: La Niña is favored to develop during September - October 2016, with about a 55-60% chance of La Niña during the fall and winter 2016-17.
ENSO-neutral conditions were observed during the past month, as indicated by near-to-below average surface temperatures (SST) across the eastern equatorial Pacific Ocean. While the Niño-4 region was slightly above average, the other Niño indices were either slightly below average or near zero during June. Below-average subsurface temperatures continued and extended to the surface in parts of the central and eastern equatorial Pacific. Atmospheric anomalies over the tropical Pacific Ocean also indicated ENSO-neutral conditions. The traditional Southern Oscillation index was slightly positive while the equatorial Southern Oscillation index was near zero. The upper and lower-level winds were both near average across most of the tropical Pacific. Convection was slightly suppressed over portions of the western tropical Pacific and enhanced over part of Indonesia. Collectively, these atmospheric and oceanic anomalies reflect ENSO-neutral conditions.
Many models favor La Niña (3-month average Niño-3.4 index less than or equal to -0.5°C) by the end of the Northern Hemisphere summer, continuing during fall and lasting into winter. Statistical models predict a later onset time (i.e., mid-fall) than dynamical models, and also predict a relatively weaker event. The forecaster consensus is somewhat of a compromise between the two model types, favoring La Niña onset during the September-October season, and predicting a weak event (Niño-3.4 index between -0.5°C and -1.0°C), if an event were to form. Overall, ENSO-neutral conditions currently prevail and La Niña is favored to develop by September - October 2016, with about a 55-60% chance of La Niña during the fall and winter 2016-17.
Most landmasses will experience average wind conditions for the month.
Much of the northern half of the northern hemisphere should be above normal while the mid-latitudes and tropics should be slightly below normal and the southern latitudes near normal except much of Australia and New Zealand and southern South America and Southern Africa should be below normal.
Much of Central North America and South America are forecast as usually low while similar conditions prevail in much of Africa and China and Central Asia. Warm episodes are limited to Western Europe, the eastern Arctic, and the eastern South Pacific and insular SE Asia and southwestern USA and the Pacific from east to west from Hawaii south to near the equator.
In the western hemisphere low precipitation events are forecast for the SE Florida and around the Gulf states of the USA and southeastern Caribbean and northern South America. Higher than normal rainfall events area also expected in Argentina and Bolivia. Usual high is forecast for Hawaii to very unusually high just to the south of Hawaii.
In SE Asia and unusually low rainfall is forecast through the western island portion of the region and southern China. Also in the Central Pacific both above and below the equator and also in northern Indonesia unusually high rainfall is expected.
Extreme rainfall events are possible in Ethiopia and also in the interior of West Africa (Mali, Burkina Faso and Nigeria) and eastern Saudi Arabia and Kuwait and southern Iraq as well as eastern Iran and western Afghanistan across to far western China. Through much of Europe and continental north Asia usual normal to usual high conditions prevail with extreme rainfall possible in northern Spain and southern France.
Warmer than normal conditions prevail in the western North Atlantic and near normal conditions elsewhere. In the South Atlantic warmer than normal conditions prevail except along the coast of southern Brazil and Argentina that are cooler than normal.
The Northern Pacific is near normal with ENSO neutral conditions prevailing with cooler to near normal waters in the eastern tropical Pacific. The far northern Pacific should be considerably warmer than normal as well as the Arctic sea. The South Pacific is warmer than normal off the South American coast and also in the western South Pacific near Australia and New Zealand while the central South Pacific is near normal.
The Indian Ocean is warmer than normal from north to south in the eastern region near Indonesia, and normal to cooler than normal South of India and Sri Lanka with cooler than normal water off the coast of Africa and also off the coast of southwestern Australia.
North and South America near normal with slightly wetter conditions in Central North America and also northwest South America and part of western Mexico and northern Brazil into Suriname and Guyana.
Southeast Asia looks near normal north of the Equator and wetter than normal south of Equator while India is normal to slightly drier than normal. Much of Bangladesh and western Myanmar is likely to be wetter than normal and most of southern China wetter than normal and north Asia near normal to slightly wetter than normal.
Much of Africa should be near normal except from Cameroon and to the west that should be wetter than normal. The Middle East and western central Asia should be near normal. Europe should be near normal.
Much of North America, the Caribbean, and Central and northern South America should be warmer than normal except for western Mexico that should be cooler than normal. Argentina and Southern Brazil should be cooler than normal.
New Zealand the eastern third and northern part of Australia should be warmer than normal and southwestern and central Australia cooler than normal and all of east and Southeast Asia should be warmer than normal with India and eastern Pakistan near normal. Southwest India should be warmer than normal as well as western China and Tibet.
Central Africa should be cooler than normal and Southern Africa warmer than normal. The Middle East and Iran and Afghanistan should be cooler than normal. Northern Asia to the Arctic should be considerably warmer than normal. Most of Europe should be near normal.