Colorado State University hurricane researchers have revised their early-April forecast and are now predicting a near-average Atlantic hurricane season, which officially runs from today to Nov. 30.
Fourteen named storms – including the first, Subtropical Storm Alberto, which formed in May – are predicted this year. Of those, the forecast team expects six to become hurricanes and two to reach major hurricane strength (Saffir/Simpson category 3-4-5) with sustained winds of 111 mph or greater.
In explaining the downgraded forecast, the CSU Tropical Meteorology Project team states that a weak La Niña this past winter has dissipated. It is possible a weak El Niño will develop by the peak of the Atlantic hurricane season (August-October), but the team thinks that neutral ENSO (El Niño-Southern Oscillation) conditions are more likely this year. El Niño tends to increase upper-level westerly winds across the Caribbean into the tropical Atlantic, tearing apart hurricanes as they start to form.
The tropical Atlantic has cooled unusually over the past two months and is now colder than normal, the forecast team reports. In addition to providing less fuel for tropical cyclone formation and intensification, cooler tropical Atlantic sea surface temperatures are associated with a more stable atmosphere and drier air, both of which suppress organized thunderstorm activity necessary for hurricane development. According to the team, the far North Atlantic also remains colder than normal, which may indicate a negative phase of the Atlantic Multi-decadal Oscillation.
The team bases its forecasts on more than 60 years of historical data that include Atlantic sea surface temperatures, sea level pressures, vertical wind shear levels (the change in wind direction and speed with height in the atmosphere), El Niño (warming of waters in the central and eastern tropical Pacific), and other factors.
The researchers predict that 2018 hurricane activity will be about 100 percent of the average season. By comparison, the extremely active 2017 season was about 245 percent of the average season. More forecast updates will be issued by the CSU team on July 2 and Aug. 2.