2021 Hurricane Season Predictions

Hurricane season begins on June 1, 2021 and will last until 30 November. The predictions for 2021 will be refined as the season moves closer, and then throughout the summer months. For now let’s looks at some basic details about the anticipation for storm activity in the 2021 Hurricane Season.

Hurricane / Tropical Cyclone Names for 2021

Forecast for 2021 Hurricane Activity

Forecast Parameters	CSU Forecast for 2021	Average for 1981-2010
Named Storms	17	12.1
Named Storm Days	80	59.4
Hurricanes	8	6.4
Hurricane Days	35	24.2
Major Hurricanes	4	2.7
Major Hurricane Days	9	6.2
Accumulated Cyclone Energy+	150	106
+A measure of a named storm’s potential for wind and storm surge destruction defined as the sum of the square of a named storm’s maximum wind speed (in 104 knots2) for each 6-hour period of its existence. Data reference: University of Colorado

Preparing for Severe Storms

Hurricanes are a stressful and dangerous part of life in the southeastern United States. Storms can impact areas as far north as New York or Canada, but the most commonly affected regions are along the Florida coastlines, reaching upward to Virginia on the Atlantic and as far west as Texas on the Gulf of Mexico coast. Preparing your family and property for a storm is a practice that has proven effective in saving lives and preventing property damage where possible. Cyclone.City has numerous articles on this subject, that are free to use and share.

DESCRIPTION OF CLIMATE FACTORS INFLUENCING ATLANTIC HURRICANE ACTIVITY

The following information is provided courtesy of the University of Colorado’s ongoing research into seasonal hurricane forecasting

Forecast Factors

In 1984, Dr Bill Gray at Colorado State University documented that Atlantic hurricane activity responded to a variety of large-scale atmospheric and oceanic parameters spanning various portions of the globe. These large-scale factors interact with the global climate system in such a way that then alter the environment of the tropical Atlantic, where most major hurricanes develop and intensify. For example, hurricanes are more likely to develop when they traverse through an environment of low vertical wind shear (the change in wind direction and speed with height in the atmosphere), high sea surface temperatures and high mid-level moisture. Several parameters that have been documented to impact Atlantic hurricanes are discussed here in more detail.

Atlantic Ocean Thermodynamics

A warmer-than-normal tropical North Atlantic Ocean is known to typically create conditions more favorable for hurricane formation and intensification. In addition to enhancing latent and sensible heat fluxes that fuel tropical cyclones, a warmer tropical North Atlantic also drives lower pressures and reduced low-level trade winds, which also feed back to a more conducive environment for hurricanes.

It is important to note that the warming of the tropical North Atlantic Ocean also be measured relative to warming in other areas. One frequently utilized metric is relative sea surface temperature, which measures the difference between tropical North Atlantic Ocean sea surface temperatures and sea surface temperatures in the rest of the tropics (Vecchi et al. 2008). This index is important because it dictates where anomalous rising and sinking motion is likely to occur. When the tropical North Atlantic Ocean is anomalously warmer than the remainder of the tropics, anomalous rising motion is likely in this area, favoring enhanced tropical cyclone activity.

An additional index that is often utilized to assess the favorability of the tropical North Atlantic Ocean is the Atlantic Meridional Mode (AMM) (Kossin and Vimont 2007). The AMM assesses both the thermodynamic and dynamic state of the tropical North Atlantic Ocean through analysis of low-level winds as well as sea surface temperatures. A positive phase of the AMM is associated with a warmer tropical North Atlantic relative to the tropical South Atlantic, as well as with reduced trade winds in the tropical North Atlantic. Positive phases of the AMM are generally characterized by above-normal Atlantic hurricane activity.

El Niño Southern Oscillation

At the interannual timescale, the prime driver of Atlantic tropical cyclone variability is generally considered to be El Niño Southern Oscillation (ENSO). ENSO is driven by changes in ocean temperature in the tropical Pacific, where above average conditions (El Niño) in the Central and Eastern Pacific shift the convective activity in the tropical Pacific eastward, and modify the Walker cell throughout the tropics. The influence of ENSO on Atlantic tropical cyclone activity is well documented and is understood to occur mainly through local changes in vertical wind shear: during El Niño (La Niña) conditions, the eastward (westward) shift in convection in the tropical Pacific leads to anomalous upper-level westerlies (easterlies) over the Atlantic, which then increases (decreases) the vertical wind shear, thus decreasing (increasing) tropical cyclone activity.

Sahel Precipitation

Changes in convective precipitation over the Sahel region has been shown to impact zonal winds in the upper-troposphere, which in turn modulate vertical wind shear over the Main Development Region and influence the conditions of cyclogenesis over the tropical Atlantic. It is possible that changes in the nature of the African Easterly Waves coming off the African continent might also be playing a role. Years with higher Sahel rainfall tend to be associated with more active hurricane seasons. The influence of the Sahel precipitation is mostly felt when the thermodynamical conditions over the tropical Atlantic are not conducive to hurricane formation.

Saharan Dust

Dust outbreaks from West Africa impact tropical cyclone activity by reducing Atlantic tropical sea surface temperatures ahead of the hurricane season. Episodes of dust outbreak are also associated with extremely dry air coming from the Sahara, another factor detrimental to cyclone formation.