April’s Tropical Storm Arlene and June’s Tropical Storm Bret and Tropical Storm Cindy are included in the seasonal forecast numbers in the outlook.
The updated forecast is above the 30-year historical average (1981-2010) for the Atlantic Basin of 12 named storms, six hurricanes and three major hurricanes.
CSU’s latest forecast is a bit higher than the last update from June 1 that called for 14 named storms and six hurricanes. It’s significantly greater than the initial April forecast of 11 named storms and four hurricanes.
Warm water temperatures in the tropical and subtropical Atlantic Ocean along with the dwindling chance of El Niño’s development later this summer are the reasons why the forecast has steadily nudged upward.
“A warmer-than-normal tropical Atlantic is generally associated with lower surface pressures, increased mid-level moisture and weaker trade winds, creating a more conducive dynamic and thermodynamic environment for hurricane formation and intensification,” said the CSU team.
2017 Atlantic hurricane season names.
Widespread and hostile upper-level winds typically associated with El Niño will also be a no-show during the heart of the hurricane season ahead. That said, unfavorable winds aloft still occur at times each season in the Atlantic basin no matter whether El Niño is present or not.
CSU found six years since 1950 that most closely resemble what is expected in the atmosphere above and waters of the Atlantic basin during August-October 2017. Those years included 1953, 1969, 1979, 2004, 2006 and 2012. The average of those six seasons is very close to CSU forecast for 2017.
The Weather Company, an IBM business, updated its seasonal forecast in June and also expects a total of 15 named storms, eight hurricanes and three major hurricanes this season. This is an increase from its earlier forecasts as well, mainly due to the same factors stated in the CSU outlook.
The official Atlantic hurricane season begins June 1 and runs through Nov. 30. Occasionally, storms can form outside those months as happened this year with Tropical Storm Arlene. This also occurred last season with January’s Hurricane Alex and late May’s Tropical Storm Bonnie.