The Atlantic hurricane season begins June 1 and ends Nov. 30. Colorado State University expects 13 more named storms, six hurricanes and two major hurricanes, a slight reduction from its initial forecast. This is near the 30-year average for the number of hurricanes and tropical storms in the Atlantic Basin. Below-average sea-surface temperatures are expected to influence hurricane season.

The National Oceanic and Atmospheric Administration’s 2018 outlook, released May 24, calls for a 75 percent chance that the 2018 season will be near or above normal range.

An average season has about 12 named storms, 6 of which become hurricanes, and 3 of which become major hurricanes of Category 3 or above. The primary reason for the forecast change is the cooling of sea surface temperatures in the Tropical Atlantic Ocean according to Dr. Phil Klotzbach, a tropical scientist at CSU.

“Overall, the SST anomaly pattern now is less conducive for an active Atlantic hurricane season than was present in late March,” the CSU outlook said.

The cooler-than-average waters in the tropical Atlantic are being driven by northerly winds around the eastern periphery of a strong area of high pressure over the eastern and central Atlantic Ocean. On the western periphery of this high, southerly winds have led to above-average water temperatures off the U.S. East Coast. “If the tropical Atlantic were to remain anomalously cool or if El Niño were to develop unexpectedly, the seasonal forecast would be lowered with our July or August updates. However, if the tropical Atlantic were to anomalously warm and the tropical Pacific were to remain neutral, the seasonal forecast could be increased in future updates,” CSU concluded.