EL NIÑO/SOUTHERN OSCILLATION (ENSO) DISCUSSION 12/9/04

[CaptinCrunch]

EL NIÑO/SOUTHERN OSCILLATION (ENSO)
DIAGNOSTIC DISCUSSION

issued by
CLIMATE PREDICTION CENTER/NCEP
December 9, 2004

Synopsis: Weak warm-episode (El Niño) conditions are expected to continue into early 2005.

Positive sea surface temperature (SST) anomalies greater than +0.5°C (~1°F) persisted across most of the central and western equatorial Pacific during November 2004 (Fig. 1). By early December, positive equatorial SST anomalies greater than +1°C (~2°F) were found from 160°E eastward to 155°W and locally in areas between 155°W and the South American coast (Fig. 2). The pattern of anomalous warmth in the equatorial Pacific in recent months and the most recent 5-month running mean value of the Southern Oscillation Index (-0.6) indicate that a weak warm (El Niño) episode has developed.

Since late 2003 MJO activity has resulted in week-to-week and month-to-month variability in many atmospheric and oceanic indices. In the past few months the warmth in the central equatorial Pacific has supported eastward shifts of enhanced convection associated with the convectively active phase of the Madden-Julian Oscillation (MJO) across the western equatorial Pacific. This activity has been associated with periods of weaker-than-average easterlies that initiated eastward-propagating oceanic Kelvin waves. This intraseasonal variability has been superposed on 1) an upward trend in SST anomalies east of the date line (Fig. 3) and 2) a gradual increase and eastward shift in the upper-ocean heat content anomalies during the last year (Fig. 4). Based on the recent evolution of oceanic and atmospheric conditions and on a majority of the statistical and coupled model forecasts, it seems most likely that weak warm episode (El Niño) conditions will persist through early 2005. However, there is considerable uncertainty concerning future developments in the extreme eastern equatorial Pacific (the classical El Niño region).

Expected global impacts include drier-than-average conditions over Indonesia (through early 2005), northern and northeastern Australia (December 2004-February 2005), and southeastern Africa (December 2004-March 2005). If the warming in the tropical Pacific strengthens and spreads eastward to the South American coast, then wetter-than-average conditions would be expected in coastal sections of Ecuador and northern Peru during the first few months of 2005, and drier-than-average conditions would be expected to develop in the eastern Amazon late this year and spread to Northeast Brazil during February through April 2005.

El Niño wintertime impacts over the United States vary considerably depending on the character (distribution and intensity) of the warming in the tropical Pacific. Composite impacts for selected ranges of the ONI for El Niño episodes since 1950 (Fig. 5) show that the spatial extent of warmer-than-average (wetter-than-average) conditions increases across the northern (southern) United States, as the strength of El Niño increases. The current warming in the tropical Pacific is expected to continue through the upcoming winter, with models indicating an ONI in the range of +0.5ºC to +1.2ºC. Thus, the winter outlook for the United States (Fig. 6) is a blend of the composite impacts for comparable historical El Niño episodes and the effects of long-term trends. Warmer-than-average conditions are expected in the West and in the northern Plains, while cooler and wetter-than-average conditions are expected for portions of the South and Southeast.

[Suncat]

December has been warm and wet for the the Triangle area of NC so far. It's hard to get into the Christmas spirit when the outside temperatures are in the 50's A little cold weather would be nice...and some snow would be nicer (hold the ice)

[gboudx]

To some people, the 50's would be considered "cold".

[HURRICANELONNY]

As soon as they talk about the variables for a weak El Nino the SOI jumps positive. I don't see a true El Nino this year so who knows what the weather will be in each sector of the country. I remember they (NWS) called for cooler and wetter for South Florida this year. I can't remember the last time it rained here besides a quick shower. Have to wait and see how it pans out this year...