August 2012: Earth's 4th warmest August on record

August 2012 was the globe's 4th warmest August on record, according to the National Oceanic and Atmospheric Administration's National Climatic Data Center (NCDC). NASA rated August 2012 the 6th warmest on record. August 2012 global land temperatures were the 2nd warmest on record, and global ocean temperatures were the 5th warmest on record. August 2012 was the 330th consecutive month with global temperatures warmer than the 20th century average; the last time global temperatures were below average was February 1985. Global satellite-measured temperatures in August for the lowest 8 km of the atmosphere were 3rd warmest in the 34-year record, according to the University of Alabama Huntsville (UAH). Wunderground's weather historian, Christopher C. Burt, has a comprehensive post on the notable weather events of August in his August 2012 Global Weather Extremes Summary.

Figure 1. Departure of temperature from average for August 2012. Most areas of the world experienced much higher-than-average monthly temperatures, including much of Canada, Southeast Europe, and Western Asia. Central Russia was much cooler than average. Image credit: National Climatic Data Center (NCDC) .

El Niño watch continues
Sea surface temperatures were at 0.5°C above average as of September 17 in the equatorial Pacific off the coast of South America, and have been near or above the 0.5°C above average--the threshold needed for a weak El Niño event--since the beginning of July. However, winds, pressures, and cloud cover over the region have not responded in the fashion typically associated with an El Niño, and NOAA's Climate Prediction Center (CPC) classified conditions as being neutral in their September 6 El Niño discussion. They continued their El Niño watch, and gave a 69% chance that an El Niño event will be in place by the end of September. El Niño conditions tend to decrease Atlantic hurricane activity, by increasing wind shear over the tropical Atlantic. Wind shear has been close to average over the tropical Atlantic since the beginning of hurricane season in June. However, the past few runs of the GFS model have predicted a significant rise in wind shear over the Caribbean and tropical Atlantic by early October, which may represent El Niño finally beginning to kick in and affect the atmospheric circulation over the Atlantic.


Figure 2. Arctic sea ice extent as of September 18, 2012 (black line) compared to the previous record low years, in millions of square kilometers. This year's extent is far below any previous year, and is close to its minimum for the year. Satellite measurements of ice extent began in 1979. Image credit: Danish Meteorological Institute.

Arctic sea ice falls to all-time record low during August
August 2012 Arctic sea ice extent reached its lowest August extent in the 35-year satellite record, according to the National Snow and Ice Data Center (NSIDC). The new sea ice record was set on August 26, a full three weeks before the usual end of the melting season. Every major scientific institution that tracks Arctic sea ice agrees that new records for low ice area, extent, and volume have been set (see the comprehensive collection of sea ice graphs here.) Satellite records of sea ice extent date back to 1979, though a 2011 study by Kinnard et al. shows that the Arctic hasn't seen a melt like this for at least 1,450 years (see a more detailed article on this over at skepticalscience.com.) The latest September 18, 2012 extent of 3.5 million square kilometers is approximately a 50% reduction in the area of Arctic covered by sea ice, compared to the average from 1979 - 2000. The amount of open ocean exposed this September compared to September 1980 is about 43% of the size of the contiguous United States. The ice extent is close to its minimum for the year, and should start in increase within the next week or two, but that open water over the Arctic will provide a significant amount of heat and moisture to the atmosphere over the next few months that will significantly alter weather patterns. One possible impact may be an increase in the intensity and duration of extreme weather events during fall and winter.


Video 1. This animation shows the 2012 time-series of ice extent using sea ice concentration data from the DMSP SSMI/S satellite sensor. The black area represents the daily average (median) sea ice extent over the 1979-2000 time period. Layered over top of that are the daily satellite measurements from January 1 – September 14, 2012. A rapid melt begins in July, whereby the 2012 ice extents fall far below the historical average. Source: NOAA's Environmental Visualization Laboratory.

Nadine approaching the Azores
Long-lived Tropical Storm Nadine is headed northeastwards on a track that will bring the storm close to the Azores Islands on Wednesday and Thursday. A tropical storm watch has been posted for the islands of Flores and Corvo in the northwestern Azores. Steering currents for Nadine are expected to weaken on Wednesday, and the storm will move slowly and erratically for many days in the Central Atlantic late this week and early next week. On Friday, Nadine will become tangled up with an upper-level low pressure system, and the storm may partially or fully convert to an extratropical storm. By this weekend, the GFS and ECMWF models predict Nadine will move southwestward over warmer waters, and it could become fully tropical again.

Elsewhere in the Atlantic, thunderstorm activity associated with a tropical wave that moved through the Lesser Antilles Islands yesterday (92L) has diminished, and this wave is no longer a threat to develop. None of the reliable computers models is showing development of a new tropical cyclone in the Atlantic through September 24.

Jeff Masters