El Ni�o is fading

El Ni�o has peaked and is likely to slowly decline over the coming months, according to the latest forecasts issued by NOAA and the Australian Bureau of Meteorology. The strength of an El Ni�o is gauged by how warm the Equatorial Pacific waters off the coast of South America get. These Sea Surface Temperatures (SSTs) peaked at 1.2 �C above average in late November, and stayed high through December, as a surge of westerly winds pushed warm water to the coast of South America. The winds at the surface have turned more easterly in the past two weeks, which has allowed the SSTs to cool dramatically (Figure 1). It is still possible that one more surge in westerly winds might reinforce the warm waters at the South American coast, but the consensus of the El Ni�o computer forecast models is that this El Ni�o is all done. This is the usual time of year that El Ni�o begins to fail, and we can expect a slow return to neutral conditions over the next six months. By August, expect SSTs off the coast of Peru to drop below 0.5 �C above average, the threshold for an El Ni�o. The way SSTs have dropped in the past week, the demise of El Ni�o could come much sooner, perhaps by June. In any case, El Ni�o will probably not die fast enough to significantly alter the weather patterns we've seen this winter. Expect continued above normal temperatures in North America and Europe, dry conditions in Australia and Indonesia, and wet weather in Peru and southern Brazil for the next two months.


Figure 1. Departure of Sea Surface Temperature (SST) from average for the week centered on December 27, 2006 (top) and January 3, 2007 (bottom). Images taken from a 12-week SST animation courtesy of NOAA's Climate Prediction Center.

The demise of El Ni�o is bad news for those affected by the Atlantic hurricane season. El Ni�o conditions substantially dampen hurricane activity in the Atlantic, and the return to El Ni�o-neutral conditions by August could make for an active hurricane season. The pre-season Atlantic hurricane season forecast for 2007 issued by Bill Gray's team at Colorado State anticipated the demise of El Ni�o for 2007. The forecast calls for 14 named storms, 7 hurricanes, and 3 intense hurricanes (an average season has 10 named storms, 6 hurricanes, and 2 intense hurricanes). An above normal chance of a major hurricane hitting the U.S. is seen, both along the East Coast (40% chance, 31% chance is normal) and the Gulf Coast (40% chance, 30% chance is average). The good news for those of you affected by Atlantic hurricanes is that tropical Atlantic SSTs have decreased substantially during the past few months. These SSTs were about 1.0 �C above normal in October, but have fallen to about 0.5 �C above normal. Comparison of the SSTs this winter in December vs. last winter (Figure 2) shows that temperatures are 0 - 0.5 �C warmer in the Caribbean this winter, but about 0.5 �C cooler between Africa and the Lesser Antilles. That's still plenty of extra heat to fuel the hurricanes of 2007, but the downward trend in SSTs over the Atlantic this winter is encouraging.

Figure 2. The difference in Sea Surface Temperature (SST) from December 2006 to December 2005. Blue and purple colors denote where it is colder this winter than last winter. Image credit: NOAA.

Snow in New York City!
Well, it wasn't much. A few flurries whitened the skies over New York City on Wednesday January 10, bringing an official trace of snow to the city. It was the first trace of snow this winter for the city, breaking the record set in 1877-1878, when the first trace arrived on January 4. New York City's first chance at accumulating snow doesn't appear likely to happen until January 22, at the earliest.

Jeff Masters