The overall recent warming of the North Atlantic, particularly in the northeastern sector and the Atlantic Main Tropical Cyclone Development Region may be, in large part, due a combination of the Atlantic Multi-decadal Oscillation (AMO) being in its warm phase which raises the base sea surface temperatures in the North Atlantic and warming resulting from the recent reduced trade winds in the tropics.
Sea surface temperature (SST) anomalies in the Tropical North Atlantic have been increasing since April due mainly to a weakening and southward displacement of the Azores-Bermuda ridge. This weakening has reduced the trade winds.
The dominant cause of the warm SSTs is due to weather patterns that reduced surface wind speed, which reduced evaporative cooling, and less cloudiness.
Other factors such as CO2 emissions, lower amount of sulfate particles from cleaner shipping fuels, Hunga-Tonga eruption, and low levels of African dust likely only had a minor role.
Since late June, the Azores-Bermuda ridge has begun to restrengthen and SSTs have fallen, however, they remain warmer than normal.