October 25, 2006
El Niño Status and Forecast from CLIMAS
El Niño conditions have persisted in the tropical Pacific Ocean this fall and are expected to continue into spring 2007. Positive equatorial sea surface temperature (SST) anomalies greater than 1 degree Fahrenheit have been observed in most of the equatorial Pacific since early September, with departures exceeding 2 degrees F in the central Pacific. The latest SST departures in all of the Niño regions are currently greater than 1 degree F.
In September the Southern Oscillation Index (SOI) was negative for the fifth consecutive month, with the three–month running mean now at –1.0 for the second month in a row (Figure 11a). According to CPC, these collective oceanic and atmospheric anomalies are consistent with the early stages of warm-episode (El Niño) conditions in the tropical Pacific. Over the past several months most of the other ENSO model forecasts (not shown) have trended toward warmer conditions in the tropical Pacific and are favoring El Niño conditions through the winter into spring 2007.
The probabilistic forecast issued by the IRI is in agreement, predicting an approximately 80 percent chance of El Niño conditions through February 2007, followed by a gradual return to ENSO-neutral conditions late in the spring or early in the summer (Figure 11b). According to the CPC, typical El Niño effects are likely to develop over North America during the upcoming winter season, including warmer-than-average conditions over western and central Canada and over the northern and western United States; wetter-than-average conditions in the southern tier of states including the Southwest and parts of the U.S. Gulf Coast and Florida; and drier-than-average conditions in the Ohio Valley and the Pacific Northwest.
Long-lead precipitation outlooks from the NOAA-CPC call for increased chances of above-average precipitation in southern New Mexico and southeastern Arizona during November–January, and for wetter-than-average conditions to extend westward and northward during the winter and spring to include the entire Southwest during January–April (Figure 9a–d). The area of greatest probability of above-average precipitation (greater than 40 percent) is expected to be along the Mexican border, gradually moving from southern Texas in the fall towards the West to include much of southern New Mexico and southern Arizona during the winter and spring. Wetter-than-average conditions are also expected to prevail in Florida and parts of the Southeast through early spring. Below-average precipitation is expected in the Pacific Northwest and parts of the Midwest and Southeast during November–April.
© 2006 Arizona Board of Regents. CLIMAS is part of the Institute for the Study of Planet Earth at the University of Arizona.
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Document located at: http://www.ispe.arizona.edu/climas/forecasts/swforecasts.html