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ENSO 2009-10: Chances of El Niño increased
Recent development of oceanic and atmospheric processes in the equatorial Pacific corresponds to a transitional phase to an El Niño event. SSTs in the equatorial Pacific Ocean continue to increase, with positive SST anomalies across much of the region. The upper ocean heat content also continues its upward trend. The Hawaiian index has dropped sharply in May, and the westerly winds intensified.All these increased the confidence factor that El Niño conditions are going to be present during the winter of 2010 (CF = 70). Most likely, however, it will be a weak El Niño event, similar to that of 1963-64.
Summer 2009 forecast for Europe
In the summer of 2009, temperatures over much of Europe are forecast to be above average. The CFs for above normal temperatures are higher for central Europe. In Scandinavia, summer temperatures will probably be near average, somewhat colder than normal on the north and warmer than normal on the south. In the eastern Mediterranean, summer temperatures are expected to be below the average for the past 20 years. Although much of Europe is likely to be warmer than average, no heat waves are expected. Precipitation is forecast to be close to average.
Summer 2009 forecast for North America
Warmer than normal temperatures are expected over much of the interior United States. A colder than normal summer is forecast for the Atlantic coastal areas of the United States, particularly the Northeast. Most of the contiguous United States is also expected to be dryer than normal. A slightly increased likelihood of wetter than normal conditions exists for the area west of the Great Lakes and the Southwest. Although the monsoon is expected to be wet, it may start later than normal this summer.
ENSO status and forecast for summer 2009 – winter 2010
The latest ENSO status is a transition from a weak-to-moderate La Niña event to a neutral state. There is much uncertainty, however, about where the ENSO cycle is heading. The signals are mixed, with some predictors indicating a possibility of an El Niño event later this year, while others suggesting that the La Niña event may linger even longer. Thus, a positive subsurface temperature anomaly in the western equatorial Pacific shifted eastward and closer to the surface, as prior to El Niño events. On the other hand, the Hawaiian index suggests that the chances of having an El Niño event during the winter of 2010 are quite slim. ENSO models show a wide range of outputs.
Review of winter 2009 in Europe
The winter of 2009 was noticebly colder than the previous two winters. Temperature anomalies were generally below average in western Europe and above average in eastern Europe. Particularly cold spell occurred in late December - early January. During that period a high pressure cell formed in the area north of the British Isles causing an advection of frigid Arctic air. Total amount of precipitation during the winter was below normal in northern Europe and above normal in the Mediterranean.
Review of winter 2009 in the North Atlantic
Although the North Atlantic Oscillation was in the neutral phase, the cyclonic activity over the ocean was enhanced. The storms were traveling along their more northern trajectories bringing warm Atlantic air to the Norwegian and Barents seas. The Northwest Atlantic was also warmer than normal this winter in terms of SST anomalies and close to normal in terms of sea-ice extent. While positive SST anomalies dominated north of 30N, the North Atlantic as a whole cooled down substantially. Still, it is probably too early to declare an end of the current positive phase of the Atlantic Multidecadal Oscillation.
Review of winter 2009 in North America
Atmospheric circulation over North America was characterized by a negative PNA index. Mean winter value of the index was the lowest since 1979. Winter temperatures for the contiguous United States and Canada were close to average. Anomalously warm temperatures were observed in the southern United States and anomalously cold temperatures in a band stretching from western Canada to the Midwestern United States. It was the fifth driest December-February period on record for the contiguous United States. Texas had its driest winter ever and the Southeast experienced its 10th driest winter. Despite the overall dryness, there were two major flooding events during the winter season.
Review of winter 2009 in the North Pacific
As predicted, the PDO index in the winter of 2009 was strongly negative. In accordance with the negative PDO phase, a pool of anomalously warm waters was observed in the east-central North Pacific, with negative SST anomalies to the north, east and south of it. The Aleutian low was extremely weak. Average sea level pressure over the North Pacific was the highest since 1907. This strongly suggests a possible climate regime shift in the basin.
