The Azores High is a semipermanent area of high atmospheric pressure centered over the subtropical North Atlantic, typically near the Azores archipelago. It is one of the most important weather-shaping features in the Northern Hemisphere, steering storm tracks across Europe, driving the trade winds that push sailing ships and Saharan dust across the ocean, and determining whether Iberia and North Africa get rain or drought in a given season. Recent research has found that this high-pressure system has been expanding in ways not seen in at least a thousand years, with consequences that reach from Mediterranean agriculture to mountaintop cloud forests.
How the Azores High Forms
The Azores High exists because of the way Earth’s atmosphere circulates heat from the tropics toward the poles. Warm, moist air rises near the equator, flows poleward at high altitude, and then sinks back toward the surface in the subtropics, roughly between 25° and 35° latitude. That descending air compresses and warms as it drops, creating a broad dome of high pressure at the surface. The Azores High represents this descending branch of the large-scale tropical circulation over the North Atlantic, and increasing pressure within it is taken as evidence that this broader circulation pattern has been intensifying since the 1950s.1Theoretical and Applied Climatology. Changes in Hadley circulation, the Azores high and winter precipitation over tropical northeast Africa
Because the air inside the high is descending, it suppresses cloud formation and rainfall. That is why the subtropical Atlantic under the Azores High is often brilliantly clear. The high is not a static dome, though. It breathes with the seasons, shifts its center, and pulses in strength from week to week. Those fluctuations ripple outward and affect weather patterns across an enormous area, from the Sahel to Scandinavia.
Seasonal Migration and European Weather
In summer, the Azores High swells and shifts northward, sometimes extending ridges of high pressure deep into western Europe. When that happens, it blocks Atlantic storm systems from reaching the continent, producing the prolonged dry spells and heat that define Mediterranean summers. Southern Portugal, Spain, and Morocco all sit under its influence during these months, receiving essentially no rainfall. The high’s northward reach in summer is also why the British Isles and France can get extended warm, dry stretches, though they sit at the fringe of the system and are far more likely to see the blocking pattern break down.
In winter, the Azores High contracts and retreats southward, opening a corridor for Atlantic storms to barrel into western Europe. The strength and position of the high during winter months largely determines how much rain falls on the Iberian Peninsula, Morocco, and the broader western Mediterranean. A winter in which the high remains unusually strong or sits farther north than normal will shunt storms away from these regions, producing drought. A weaker or more southerly high lets storms through, bringing the rainfall that agriculture and reservoirs depend on.
This tug-of-war between the Azores High and the Icelandic Low, the semipermanent low-pressure center near Iceland, is the essence of the North Atlantic Oscillation, one of the most studied climate patterns on the planet. When the pressure difference between the two centers is large, westerly winds are strong, northern Europe gets more storms, and southern Europe tends to be drier. When the difference is small, the pattern reverses. The Azores High is, in effect, one half of the engine that drives European winter weather.
Trade Winds, Coastal Upwelling, and the Canary Current
The clockwise circulation of air around the Azores High generates the northeast trade winds that blow steadily across the tropical and subtropical Atlantic. These winds were the invisible highways of the Age of Sail, but they also drive critical ocean processes along the African coast. As air flows equatorward along northwest Africa, it pushes surface water offshore. Cold, nutrient-rich water rises from depth to replace it, a process called coastal upwelling. The persistence and strength of this upwelling off northwest Africa is directly linked to the Azores High, which provides the trade winds flowing along the coast.2Journal of Marine Systems. Recirculation of the Canary Current in fall 2014
The upwelling zone off Morocco, Mauritania, and Senegal is one of the most biologically productive stretches of ocean on Earth, supporting enormous fisheries. Because the Azores High is strongest and farthest north in summer, the upwelling-favorable winds around the Canary Islands blow hardest and most persistently during that season, though they persist year-round.3Journal of Marine Systems. Recirculation of the Canary Current in fall 2014 Any long-term shift in the strength or position of the Azores High would reshape these winds and, by extension, the fisheries and marine ecosystems that depend on the cold, upwelled water.
The same wind-driven circulation helps define the broader North Atlantic subtropical gyre, the massive clockwise loop of currents that includes the Gulf Stream flowing northward and the Canary Current flowing southward along Africa. The Azores High sits roughly at the center of this gyre’s atmospheric forcing. Changes in wind stress from the high can alter current speeds throughout the system.
Saharan Dust Crossing the Atlantic
Every year, hundreds of millions of tons of mineral dust lift off the Sahara and travel westward across the Atlantic, sometimes reaching the Caribbean and the Amazon basin. The Azores High plays a direct role in steering this dust. Research tracking dust transport into the Caribbean has identified two distinct routes: a northern mode, in which dust mobilized from the Sahara travels westward under the control of the Azores High, and a southern mode, in which intense dust clouds from the Sahel region travel over the Gulf of Guinea before curving toward the Caribbean.4Journal of Geophysical Research Atmospheres. Saharan mineral dust transport into the Caribbean: Observed atmospheric controls and trends
The northern route matters enormously for air quality across the Atlantic islands and the Caribbean during summer, when the Azores High is strongest and the easterly flow most persistent. Dust plumes riding this path can dim skies over Barbados and Puerto Rico, degrade air quality for people with respiratory conditions, and deposit iron and phosphorus into ocean waters, fertilizing phytoplankton but also potentially feeding harmful algal blooms. The high essentially acts as a conveyor belt: when it is strong and well-positioned, the belt runs faster and pushes more dust westward. When it weakens or shifts, dust transport along the northern route slackens.
Saharan dust reaching the Amazon is a different story, largely driven by the southern mode, but the northern transport path controlled by the Azores High is the dominant one for Caribbean islands and the southeastern United States. Understanding how the high’s strength and position change over time is therefore directly relevant to public health and marine ecology across a wide swath of the tropical Atlantic.
Unprecedented Expansion Under Climate Change
One of the most striking findings in recent climate research is that the Azores High has been growing in ways that have no precedent in at least the past 1,200 years. A study combining observations, climate model simulations, and precipitation proxy records from Portugal found that winters with an extremely large Azores High have become significantly more common since the start of the industrial era, around 1850. The expansion strengthened through the twentieth century, consistent with warming driven by greenhouse gas emissions.5Nature Geoscience. Twentieth-century Azores High expansion unprecedented in the past 1,200 years
The practical consequence is felt most sharply in the western Mediterranean. When the Azores High is anomalously large in winter, it blocks moisture-bearing Atlantic storms from reaching the Iberian Peninsula. The result is anomalously dry conditions across Portugal, Spain, and neighboring regions.6Nature Geoscience. Twentieth-century Azores High expansion unprecedented in the past 1,200 years This matters for agriculture, hydropower, wildfire risk, and municipal water supplies. Iberia already experiences recurring droughts, and climate projections suggest the Azores High is expected to become even more intense by the end of the century, particularly in winter, spring, and autumn.7Renewable Energy. Climate change impact in offshore energy resources along the Spanish coasts based on a high-resolution regionally coupled model
What makes this finding especially compelling is that the proxy evidence from Portuguese cave deposits and tree rings aligns with what the models predict. The medieval period, the Little Ice Age, and other pre-industrial climate fluctuations all fall within a range of Azores High variability that is distinctly smaller than what has been measured since the mid-nineteenth century. The system appears to have shifted into a regime that the region simply has not experienced in recorded climatic history.
Threatened Cloud Forests in Macaronesia
One of the more unexpected consequences of Azores High intensification involves the cloud forests of the Macaronesian islands, the archipelagos of the Azores, Madeira, and the Canary Islands scattered across the eastern North Atlantic. These forests depend on a distinctive meteorological setup. The trade winds carry moist marine air toward the islands, and as that air rises along mountain slopes, it cools and forms a persistent blanket of low clouds known as stratocumulus. Where these clouds intercept the mountain terrain, they create the cool, dripping conditions that sustain laurel forests and other moisture-dependent ecosystems found nowhere else.
The altitude at which those clouds form is governed by the trade wind inversion, a layer of warm, subsiding air that acts as a lid on the moist marine layer below. Fog interception by trees in these zones is a major component of the local water cycle, supplementing rainfall in a region where precipitation alone would not support such lush vegetation.8Journal of Hydrology. Fog mitigates the consequences of a profligate water use strategy in a Macaronesian cloud forest tree species
As the Azores High intensifies, it strengthens the subsidence that pushes down on the atmosphere over the eastern North Atlantic. Research has documented that cloud top heights in the region have been decreasing, measured using the trade wind inversion base as a proxy. This decrease is consistent with the observed increase in subsidence accompanying Azores High intensification. Among the consequences, one of the most direct is the effect on the altitudinal distribution of the cloud forests, which may be forced to shift to lower altitudes as the cloud immersion patterns that sustain them are disrupted.9Earth Systems and Environment. Sinking of the Eastern North Atlantic Stratocumulus: Implications for the Macaronesian Cloud Forest
This is not simply a matter of forests migrating downhill. Lower on the mountain slopes, the terrain may already be occupied by different vegetation, agriculture, or human settlement. The cloud forests could find themselves squeezed between a descending cloud ceiling above and incompatible land use below. Species adapted to the narrow band of cloud immersion, some of them endemic to a single island, face a habitat that is literally shrinking from above.
Offshore Wind Energy Along the Atlantic Coast
The same persistent winds that drive upwelling and dust transport also represent a massive energy resource. Along the coasts of western North Africa and the Iberian Peninsula, the Azores High generates steady, equatorward alongshore winds that are enhanced by the thermal contrast between the cool ocean and the hot landmass of the Sahara.10Environmental Research Letters. Climate change impact on Northwestern African offshore wind energy resources These winds are among the most reliable offshore wind resources in the world, and they are a key factor in the growing interest in offshore wind farms along the Moroccan and Mauritanian coasts.
Climate projections introduce both opportunity and uncertainty. If the Azores High intensifies as expected, wind speeds along these coasts could increase, potentially boosting energy production. But “more intense” does not always mean “more predictable.” Shifts in the seasonal pattern of the high could alter when peak wind resources are available, complicating grid planning. Research modeling climate change impacts on offshore energy resources along Spain’s coasts found that the wind pattern in winter, spring, and autumn is primarily shaped by the Azores High, and that the high is projected to strengthen considerably by the end of the century.11Renewable Energy. Climate change impact in offshore energy resources along the Spanish coasts based on a high-resolution regionally coupled model
For wind farm developers and national energy planners, the behavior of the Azores High over the coming decades is not an abstract climate question. It directly determines the bankability of offshore wind projects across a large portion of the eastern Atlantic. The same system that has been steering weather and ocean currents for millennia now also steers investment decisions worth billions of euros.
How Well Climate Models Capture the System
Given how many downstream effects hinge on the Azores High, getting it right in climate models is a serious concern. Researchers have developed simplified feedback schemes to evaluate how well global climate models simulate the atmosphere-ocean-land interactions that shape the Azores High during summer.12Atmospheric Science Letters. Using feedback from summer subtropical highs to evaluate climate models The basic idea is that the high does not just sit passively in the atmosphere. It interacts with sea surface temperatures, land surface heating, and moisture patterns in ways that create feedback loops: a stronger high drives stronger trade winds, which cool the ocean surface through upwelling and evaporation, which in turn can reinforce or weaken the high itself.
Models that fail to capture these feedbacks will get the Azores High wrong, and if they get the high wrong, they will misrepresent European precipitation, North African wind patterns, dust transport, upwelling strength, and cloud forest conditions all at once. The stakes for model accuracy are unusually high because the Azores High sits at a crossroads where atmospheric, oceanic, and terrestrial processes all intersect. A bias of even a few degrees in its average position or a few hectopascals in its central pressure can cascade through the entire North Atlantic climate system.
The challenge is that subtropical highs are notoriously difficult for models to pin down. They emerge from the interplay of large-scale dynamics and regional processes, including boundary layer turbulence, low cloud formation, and land-sea temperature contrasts. Different model families handle these processes with different assumptions, and the spread in their projections for the Azores High is wider than researchers would like. This is one reason why the proxy-based reconstruction showing unprecedented expansion carries so much weight: it provides an observational anchor against which models can be calibrated, rather than relying on models alone to tell us what the future holds.
The Azores High and Atlantic Hurricane Tracks
The Azores High also influences where tropical cyclones go once they form. Hurricanes that develop in the tropical Atlantic generally move westward, steered by the easterly flow on the southern flank of the high. As they travel across the ocean, their eventual track depends heavily on where the western edge of the Azores High sits. If the high extends far west and remains strong, hurricanes are more likely to recurve into the Gulf of Mexico or make landfall along the U.S. East Coast rather than curving harmlessly out into the open Atlantic.
During summers when the Azores High is particularly robust and displaced westward, the steering flow can funnel storms toward the Caribbean and the southeastern United States. When the high is weaker or positioned farther east, storms are more likely to turn northward earlier, potentially threatening the Azores themselves or curving into the mid-Atlantic without making landfall elsewhere. Seasonal hurricane forecasters monitor the expected strength and position of the Azores High as one of several key ingredients, alongside sea surface temperatures and wind shear, when issuing their outlooks each spring.
The relationship is not deterministic. Individual storms can behave unpredictably regardless of what the broad steering pattern suggests. But across an entire hurricane season, the average configuration of the Azores High is one of the strongest statistical predictors of where storms will track. In a warming climate, with the high expected to intensify and potentially shift its mean position, the implications for hurricane risk across the Atlantic basin remain an active and consequential area of research.