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Tuesday, August 10, 2010

Jeff Masters: July SSTs in the tropical Atlantic set a new record

July SSTs in the tropical Atlantic set a new record

by Jeff Masters, WunderBlog, August 9, 2010

Sea Surface Temperatures (SSTs) in the Atlantic's Main Development Region for hurricanes had their warmest July on record, according to an analysis I did of historical SST data from the UK Hadley Center. SST data goes back to 1850, though there is much missing data before 1910 and during WWI and WWII. SSTs in the Main Development Region (10° N to 20° N and 20° W to 80° W) were 1.33 °C above average during July, beating the previous record of 1.19 °C set in July 2005. July 2010 was the sixth straight record warm month in the tropical Atlantic, and had the third warmest anomaly of any month in history. The five warmest months in history for the tropical Atlantic have all occurred this year. As I explained in detail in a post on record February SSTs in the Atlantic, the Arctic Oscillation (AO) and its close cousin, the North Atlantic Oscillation (NAO), are largely to blame for the record SSTs, though global warming and Atlantic Multidecadal Oscillation (AMO) also play a role.

The magnitude of the anomaly has increased slightly since June, because trade winds over the tropical Atlantic were at below-normal speeds during July. These lower trade wind speeds were due to the fact that the Bermuda-Azores High had below-normal surface pressures over the past month. The Bermuda-Azores High and its associated trade winds are forecast to remain at below-average strength during the next two weeks, according to the latest runs of the GFS model. This means that Atlantic SST anomalies will continue to stay at record warm levels during the remainder of August, and probably during September as well. This should significantly increase the odds of getting major hurricanes in the Atlantic during the peak part of hurricane season, mid-August through mid-October.

Figure 2. The departure of sea surface temperature (SST) from average for August 9, 2010. Image credit: NOAA/NESDIS.


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