October 2011 the globe's 8th warmest on record

October 2011 was the globe's 8th warmest October on record, according to the National Climatic Data Center (NCDC). NASA's Goddard Institute for Space Studies also rated October the 8th warmest on record. The top ten warmest Octobers since record keeping began in 1871 have all occurred since 1997. October 2011 global land temperatures were the 2nd warmest on record, and ocean temperatures were the 11th warmest on record. Global satellite-measured temperatures for the lowest 8 km of the atmosphere near average, the 19th or 12th warmest in the 34-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH).

Wunderground's weather historian, Christopher C. Burt, has a comprehensive post on the October 2011 Global Weather Extremes Summary.


Figure 1. Departure of temperature from average for October 2011. Image credit: National Climatic Data Center (NCDC).

A warm October with few extremes for the U.S.
In the contiguous U.S., where extreme weather has been the norm this year, October was remarkably normal. October 2011 ranked as the 33rd warmest October in the 117-year record. Extremes in temperature were hard to find, with no states recording a top-ten coldest or warmest October. Three states had a top-ten driest October--Louisiana, Missouri, and Iowa. Two states had a top-ten wettest October--New Hampshire and Massachusetts. Precipitation over Texas was near normal in October, making it the first month since February that was not a top-ten driest month for the state. Nevertheless, 90% of Texas remained under extreme to exceptional drought as of November 8, according to the U.S. Drought Monitor. The most significant weather event of the month in the U.S. was the October 29 - 30 Nor'easter that dumped up to 32" of snow on the Northeast, causing at least $3 billion in damage.

A weak La Niña continues
A weak La Niña event continues in the equatorial Pacific, where sea surface temperatures have ranged between 0.8 - 1.1°C below average during the first half of November. The impacts of a La Niña on U.S. weather are well-defined. It is likely that the drought in the South, especially Texas, will continue, along with above average temperatures. The Northwest can expect cooler than average temperatures, as well as the potential for another winter with a heavy snowpack across the western United States.

Arctic sea ice extent second lowest on record
Arctic sea ice extent was at its second lowest on record in October, behind 2007, according to the National Snow and Ice Data Center. October 2011 sea ice extent was 23.5% below the 1979 - 2000 average. Sea ice extent retreated to its lowest value on record during the second week of November, thanks in part to a powerful 943 mb blizzard that brought hurricane-force winds to the Chukchi Sea between Siberia and Russia, compacting and breaking up the sea ice there. Sea ice records date back to 1979.

Eastern Pacific hurricane season not over yet?
Both the tropical Atlantic and Eastern Pacific Oceans are quiet this week, and we are well past the date for the climatological formation of the season's last storm in both basins, particularly in the Eastern Pacific. A major reason for the lack of late-season activity in the Eastern Pacific is due to the cessation of African waves spawned by the African monsoon, which serve as low pressure "seeds" to get the atmosphere spinning and trigger formation of a tropical cyclone. However, the four top models for predicting formation of tropical storms unanimously agree that a tropical storm will form in the Eastern Pacific early next week, thanks to some unusual wave-like motions in the atmosphere that are generating low pressure systems over the Eastern Pacific, similar to African waves. The GFS model is forecasting that we will get not one, but two tropical storms forming in the Eastern Pacific over the next two weeks. Tropical storms are very rare in the Eastern Pacific this late in the year. Since 1949, here have been just three named storms that have formed after November 18. These three storms were an unnamed tropical storm on November 27, 1951; Tropical Storm Sharon on November 27, 1971; and Hurricane Winnie on December 5, 1983. None of these storms hit land, though the 1951 storm grazed the Baja. Next week's storm, if it forms, is expected to move west-northwest, parallel to the Mexican coast, but it is uncertain if it might pose a landfall threat or not.

Jeff Masters