The 2018 Atlantic hurricane season that officially concluded Friday was a relatively calm one for the Caribbean, and for Virgin Islanders still rebuilding after the devastation of 2017’s pair of Cat 5 storms that’s good news.
While 2018’s season brought hurricanes Florence and Michael, which caused significant damage in the southeastern U.S., it mostly gave the territory a pass. Near misses by the few storms that came near brought heavy rain and flooding, but no storm actually hit the islands. High wind shear across the Caribbean kept the region quiet, according to the National Hurricane Center and Colorado State University’s Tropical Meteorology Project.
According to the NHC, the season produced a total of 15 named storms including eight hurricanes, of which two were “major” – category 3, 4 or 5. An average season has 12 named storms, six hurricanes, and three major hurricanes.
In a season-concluding report, the Colorado State team said the 2018 season proved to be slightly above average – and more active than had been predicted.
“The 2018 Atlantic hurricane season was above-average for numbers of named storms and hurricanes, and near-normal for the number of major hurricanes,” said Phil Klotzbach, lead author of the forecast.
And that activity came despite circumstances that typically should have limited it, the CSU report said.
While El Niño did not develop, vertical wind shear in the Caribbean was much stronger than normal. Typically, when vertical wind shear is above normal in the Caribbean, it tends to inhibit formation of hurricanes throughout the tropical Atlantic. In 2018, the Caribbean was very quiet for hurricane activity, but the eastern and central tropical Atlantic were quite active.
The tropical Atlantic was cooler than normal during the peak of the hurricane season. Anomalously cool sea surface temperatures tend to inhibit Atlantic hurricane formation through several mechanisms. Cool sea surface temperatures provide less fuel for developing tropical cyclones. They also tend to be associated with higher pressure and drier mid-level air, which also suppress hurricane activity.
The NHC noted that the 2018 hurricane season was the first since 2008 to have four named storms active at the same time (Florence, Helene, Isaac and Joyce). Hurricane Florence caused catastrophic flooding in portions of North and South Carolina. Several river forecast locations in the Carolinas approached or broke their record flood level in the days and weeks following the hurricane. It took two to three weeks for many river locations to fall below flood stage, and the final river crested one month after Florence made landfall.