Each spring there are numerous government and private organizations that undertake the task of predicting the North Atlantic Hurricane season. This year, the 2021 North Atlantic hurricane forecasts are calling for another above-normal hurricane season with between 12 and 20 named storms.
What factors influence the hurricane season?
There are several large-scale atmospheric systems that tend to enhance the Atlantic hurricane season such as low vertical wind shear, high sea surface temperatures and high mid-level moisture.
Warmer than normal ocean temperatures are favorable for hurricane formation and intensification. A warmer Tropical North Atlantic also can create lower air pressures and reduced trade winds which enhance tropical development.
Another factor is the El Nino Southern Oscillation (ENSO).
ENSO is driven by changes in ocean temperature in the tropical Pacific, where warmer than average conditions (El Niño) in the Central and Eastern Pacific tend to increase vertical wind shear over the tropical North Atlantic and thus dampen tropical cyclone development. During the cooler La Niña phase, vertical wind shear over the tropical North Atlantic is reduced which tends to favor tropical cyclone development.
Changes in precipitation patterns over the Sahel region of North Africa can also affect vertical wind shear over the Atlantic hurricane producing area. Years with higher Sahel rainfall have been associated with more active hurricane seasons. Also, episodes of dust from the Sahara tend to reduce Atlantic sea surface temperature and are also associated with very dry air, both factors tend to reduce activity.
Below is a summary of the various 2021 Tropical Cyclone Forecasts for the North Atlantic:
In addition, Colorado State University also provides a forecast by county for Tropical Cyclone Impact (defined as one or more storms within 50 miles of location)