There’s been a lot of attention this spring and summer on the cool Atlantic and rightly so. According to Colorado State University’s index, the mean July 2018 AMO (Atlantic Multidecadal Oscillation) was at it’s lowest value since 1950.
The imbalance of warm Pacific, cool Atlantic through the tropics has led to stronger than normal easterly trades and so the Atlantic struggles to heat due to continued upwelling caused by the easterlies which draws cooler subsurface water up.
Let’s not forget the very cold water over the North Atlantic. It’s the combination of the cool north and tropical basin which has driven the AMO overall to the lowest July value since 1950.
It should be of no surprise that with stronger easterlies comes greater and much more frequent outbreaks of Saharan dust out over the Atlantic. The dust and increased shear has meant the hurricane season has been practically nonexistent within the MDR (main development region) this year so far.
Despite a cool tropics, the waters are still warm enough but the overall ocean-atmosphere environment is not as conducive.
We must pay close attention to the very warm waters in close to the US including the very warm waters extending from central Atlantic ( in between the cool) which extends back to the US. This area bares close watching as we enter the heart of the hurricane season.
July relative sea surface temperature (SST) (tropical Atlantic minus global tropical SST) was the coldest July value on record (since 1948). A cold Atlantic vs. the rest of the global tropics typically reduces Atlantic #hurricane activity. pic.twitter.com/5vHstgLmm5
— Philip Klotzbach (@philklotzbach) August 3, 2018
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