Synopsis: La Niña is favored to develop (~70% chance) during the Northern Hemisphere fall 2016 and slightly favored to persist (~55% chance) during winter 2016-17.
ENSO-Neutral conditions were observed during September, with negative sea surface temperatures (SSTs) anomalies expanding across the eastern equatorial Pacific Ocean by early October. All of the Niño regions cooled considerably during late September and early October, with the latest weekly value of Niño-3.4 index at -0.9°C. Subsurface temperature anomalies also decreased toward the end of the month, reflecting the strengthening of below-average temperatures at depth in the east-central equatorial Pacific. Atmospheric anomalies across the equatorial Pacific edged toward La Niña during September, with a stronger tendency toward La Niña late in the month. The traditional Southern Oscillation index and the equatorial Southern Oscillation index were positive. The lower-level winds were near average across most of the basin during the month, but enhanced easterlies were becoming more persistent west of the International Date Line. Upper-level winds were anomalously westerly near and just east of the International Date Line. Convection was weakly suppressed over the central tropical Pacific and was more enhanced over Indonesia compared to last month. Overall, the combined ocean and atmosphere system reflects ENSO-Neutral during September, but are more clearly trending toward La Niña conditions.
The multi-model averages favor borderline Neutral-La Niña conditions (3-month average Niño-3.4 index less than or equal to -0.5°C) persisting during the Northern Hemisphere fall and continuing into the winter. Because of the recent cooling in the Niño-3.4 region and signs of renewed atmospheric coupling, the forecaster consensus now favors the formation of a weak La Niña in the near term, becoming less confident that La Niña will persist through the winter. In summary, La Niña is favored to develop (~70% chance) during the Northern Hemisphere fall 2016 and slightly favored to persist (~55%% chance) during winter 2016-17.
Most landmasses will experience average wind conditions except for eastern South America and New Zealand and Tasmania and the eastern Caribbean that should all have lower than normal winds over the month. Also Northeast African parts of East Africa should have lower than normal winds for the month as well as the southern parts of West African countries.
Much of the northern half of the northern hemisphere should be below normal while the mid-latitudes and tropics should be slightly below normal and the southern latitudes near normal except much of Australia and eastern Brazil that should be below normal along with most of north and west Africa and also parts of southern Africa. New Zealand and southern South America and Southern Africa should be near 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.