Why is the 2024 Atlantic hurricane season unusually calm?

The tropics are unusually quiet right now, and there are a number of complex atmospheric and oceanic factors contributing to this. As the Atlantic hurricane season approaches its peak, the conditions that typically foster storm development are temporarily absent. Let’s take a deep dive into why we’re experiencing this quiet period and what to expect in the coming weeks.

1. Current Absence of Tropical Cyclones

There are currently no active tropical cyclones in the Atlantic basin. The absence of storms is notable, especially considering that early September is a time when tropical activity increases significantly. While the National Hurricane Center (NHC) is monitoring four areas of concern for potential development, none of these systems show strong potential for intensification in the near future.

Tracking of these systems reveals generally quiescent activity as none of them are expected to contribute significantly to the overall tropical cyclone energy, known as Total Cyclone Energy (ACE), during this quiescent period.

2. Adverse Atmospheric Conditions

One of the main reasons for the lack of storm activity is the unfavorable atmospheric conditions across much of the Atlantic. There are several factors currently working against storm development, including:

High Wind Shear: Wind shear, or the change in wind speed and direction with height, is currently very strong across large parts of the Atlantic. Wind shear can disrupt the structure of developing storms by tilting them away from the storm center or displacing storm activity. Without a vertically aligned system, a tropical cyclone cannot intensify.

Dry Air and Dust from the Sahara: The presence of dry air, commonly associated with the Saharan Air Layer (SAL), has also played a role in suppressing storm formation. The SAL brings warm, dry air from the Sahara Desert across the Atlantic, creating an environment hostile to the development of moisture-laden storms that fuel tropical cyclones. Without sufficient moisture in the atmosphere, these storms struggle to organize and strengthen.

Stable Atmospheric Conditions: In addition to dry air, stable atmospheric conditions limit thunderstorm formation, where warm air prevents cooler, moisture-laden air from rising. These stable layers inhibit the vertical development of clouds, reducing the potential for thunderstorms to cluster and form a tropical depression or storm.

3. Madden-Julian Oscillation (MJO) Phase

The Madden-Julian Oscillation (MJO), a large-scale tropical disturbance that can enhance or suppress hurricane activity, is currently in a phase that suppresses storm formation in the Atlantic. The MJO is an eastward-moving pulse of clouds and rain that circulates around the globe and influences weather patterns in the tropics.

Currently, the MJO is located over the Maritime Continent, away from the Atlantic basin, and is expected to continue to move into the Western Pacific. This phase of the MJO tends to be associated with increased convection in the Pacific Ocean and suppressed convection in the Atlantic, reducing the likelihood of tropical cyclone formation. However, later in September, the MJO is forecast to move into a more favorable position for Atlantic hurricane activity, potentially leading to an increase in storm development as the month progresses.

4. Global Model Forecasts and Seasonal Forecasts

Global weather models such as the ECMWF EPS (European Centre for Medium-Range Weather Forecasts) and GEFS (Global Ensemble Forecast System) ensembles provide insight into possible storm formation in the near future. The ECMWF model currently predicts the development of a strong African easterly wave over the next 8-9 days, which could potentially lead to storm formation as it moves off the African coast into the Atlantic.

However, GEFS forecast guidance is less aggressive on storm development and suggests that despite wave potential, strong wind shear will remain a limiting factor. The models also highlight that while conditions are currently unfavourable, they are expected to improve as September progresses, with wind shear forecast to weaken, creating a more favourable environment for storms.

Despite this lull, it is important to note that seasonal outlooks from several forecasting organizations, such as Colorado State University and the National Oceanic Atmospheric Administration, still predict an above-average hurricane season. The early part of the season was marked by multiple hurricanes through mid-August, and while activity has slowed, it is possible to see a resurgence later in the month or in October.

5. Climatic Perspective

Historically, the first two weeks of September mark the climatic peak of the Atlantic hurricane season, with most storms forming in the central and eastern tropical Atlantic. However, during this period we often observe brief quiet phases when environmental conditions align to temporarily suppress storm activity.

Looking at hurricane data since 1960, the current quiet period is not entirely unusual. Even during an active season, periods of subdued activity can occur, only to experience a sudden increase in storm formation when conditions become favorable again.

6. Outlook for the Coming Weeks

While the tropics are currently quiet, this lull is unlikely to last much longer. Forecasters expect conditions to become more favorable for storm formation by mid-September as wind shear weakens and the MJO enters a more supportive phase for Atlantic activity. Additionally, a sudden increase in storm formation is likely as the Atlantic enters its peak period.

Given that the atmosphere can change rapidly during hurricane season and multiple systems can develop rapidly after a calm period, caution is essential.

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