Ocean temperatures off the East Coast of the US are extraordinarily warm for this time of year. A region of water in the Gulf Stream 100 miles off Virginia Beach now features sea surface temperatures of 81 degrees Fahrenheit or 10 degrees (F) above average. To the south and east, in a stormy zone between Bermuda and the Bahamas, temperatures are around 77 degrees Fahrenheit or 4 degrees above average. Readings more typical of July and not at all usual for May in this region of the world ocean.
(Extremely warm sea surface temperatures ranging from 75 to 82 Fahrenheit off the US East Coast contain enough heat potential energy to support tropical storm and hurricane development during late May. Image source: Earth Nullschool.)
Ocean heat is a primary driver of tropical cyclone formation. And record warm 2016 land and ocean surfaces contributed to the January formation of hurricane Alex in the Northeastern Atlantic this year. An unprecedented January-forming hurricane that organized five months before the typical start of hurricane season on June 1. Now, a low pressure center swirling between the Bahamas and Bermuda on Thursday appears to be developing tropical or subtropical characteristics in what may become Bonnie — the second named tropical cyclone of 2016 — over the next few days.
Weather statements from the National Hurricane Center (NHC) at 2:55 PM Eastern Standard Time noted that conditions would become more favorable for tropical cyclone development over the next 24-48 hours. And the Center predicted that a tropical cyclone was 60 percent likely to form over the next two days and 70 percent likely to form over the coming five. The NHC also warned that all coastal interests from Georgia to North Carolina should monitor the progress of this developing low.
(An area of disturbed weather in the lower right hand portion of this image may form into tropical storm Bonnie over the next two to five days. Image source: The National Hurricane Center.)
Current satellite imagery indicates high, cold cloud tops associated with thunderstorm formation north of the low’s center of circulation. Forecast models indicate a west-northwest storm track that ultimately brings the low on shore near the North Carolina – South Carolina border on early Sunday morning. Models then predict that the low will stall out, hovering over the coastal Carolinas for the next 3-4 days.
If Bonnie does reach tropical storm strength it will only be the fifth time two tropical storm or hurricane strength cyclones have ever formed before June 1 since record keeping began in 1794. It’s also worth noting that the January formation of Hurricane Alex already makes the 2016 season one for the record books. Increasing ocean surface temperatures across almost all basins due to a fossil-fuel emissions based warming of the world is likely to result in a higher likelihood of such out-of-season storms all while increasing the potential maximum strength of the strongest storms. And recent events in the Pacific, Atlantic, and Indian oceans seem to bear out these predicted trends.