An extraordinary amount of heat has built up in the north Atlantic from the equator to 60ºN taking the average sea surface temperature of that whole region to a new record high of 25C or 77ºF. Multiple factors have been involved in this shocking build up in heat, and scientists are working to understand how they have interacted to cause such rapid heating of such a vast region, but underlying all of the factors is the build up of greenhouse gases in the atmosphere caused by the burning of fossil fuel. It’s not just protected locations in Florida bay that have seen temperatures exceeding 100ºF that have seen record warmth. Extreme high sea surface temperature anomalies extend from offshore of Portugal to the Labrador sea.
Through the month of July heat has continued to build up in the main development region for Atlantic basin hurricanes and the area of water with temperatures above 28.5C or 83.3ºF is now near the all time record high measured in September 2010. Because tropical and subtropical waters continue to heat up through the month of August into the middle of September, the main development region would be expected to be at record warmth at the peak of this hurricane season.
The figure below shows the monthly size of the Atlantic warm pool compared to the monthly average size for the years 1985 to the present.
Warm water has mixed well below the surface raising the ocean heat content, a measure of the heat available to support major hurricanes, to record high levels for the first of August.
Sea surface temperatures and atmospheric thermodynamics are already supportive of major hurricanes if tropical waves enter the main development region with favorable spin, low wind shear, and large moist air envelopes. July normally has a strong flow of dry dusty air off of the Sahara into the Atlantic suppressing tropical storm activity. By mid August the dry dusty flow diminishes and atmospheric conditions become more favorable for tropical storm formation. We’ll see what happens this year, but ocean conditions are already capable of supporting category 5 storms.
The latest run of the American CFS model is consistent with earlier runs of multiple American and European models in showing a pattern of above normal precipitation indicative of potential tropical storm activity extending from the Cape Verde Islands, to the main islands of the Caribbean, to the Florida Keys. Of course, if any storm gets into the steaming hot Gulf of Mexico, it means trouble.
There’s a larger than normal amount of uncertainty in this year’s Atlantic and eastern Pacific hurricane forecasts due to the interaction of El Niño and other climate related patterns such as the Pacific Decadal Oscillation (PDO) and the Atlantic Meridional Oscillation (AMO). The PDO has cooled the tropical eastern Pacific and the AMO has brought warm southerly winds across the tropical Atlantic warming the tropical and subtropical waters in the central Atlantic.
This is a unique situation and we are in uncharted waters. What we know for certain is that if any storm gets going with low shear surrounded by moist air, not Saharan air, it could rapidly intensify into a monster. Everyone living in the Caribbean, on the southeast coast of the Atlantic and the Gulf coast needs to be ready for extreme weather. Even the northeast could be impacted by major hurricanes this year.