As predicted earlier this summer, La Nina appears to be taking shape. In fact, according to NOAA’s Climate Prediction Center,
Nearly all models predict La Niña to continue at least through early 2011 (Fig. 6). However, the models continue to disagree on the eventual strength of La Niña. Based on current observations and model guidance, we expect the SST anomalies in the Niño-3.4 region to either persist near the present strength, or to strengthen into the winter as is consistent with the historical evolution of La Niña. Thus, it is likely that the peak strength of this event will be at least moderate (3-month average between –1oC to –1.4oC in Niño-3.4) to strong (3-month average of –1.5oC or less in Niño-3.4).
Expected La Niña impacts during September-November 2010 include suppressed convection over the central tropical Pacific Ocean, and enhanced convection over Indonesia. The transition into the Northern Hemisphere Fall means that La Niña will begin to exert an increasing influence on the weather and climate of the United States. These impacts include an enhanced chance of above-average precipitation in the Pacific Northwest, and below-average precipitation in the Southwest and in portions of the middle and lower Mississippi Valley and Tennessee Valley. Also, La Niña can contribute to increased Atlantic hurricane activity by decreasing the vertical wind shear over the Caribbean Sea and tropical Atlantic Ocean (see the August 5th update of the NOAA Atlantic Seasonal Hurricane Outlook), and to suppressed hurricane activity across the central and eastern tropical North Pacific.
Northwest meteorologist Mark Nelson recently posted his take on winter on his weather blog. Nelson’s reseacrh shows that we have not had a moderate to strong La Nina event since 1988-89. More recent events have all been light to moderate.
Read more about what La Nina may have in store for your area here.