Storm Kristin was not exceptional from a meteorological cyclogenesis standpoint, but it clearly illustrates how the current climate context is making certain phenomena more frequent, persistent, and impactful. We are not witnessing something unprecedented, but rather weather systems that are becoming increasingly efficient at causing damage.
From a technical perspective, Kristin resulted from a weak to moderate, yet well-organized cyclogenesis, without meeting the criteria for explosive cyclogenesis, namely a rapid drop in central pressure over a 24-hour period. It was a shallow system, with no significant vertical development. Thus, the core issue is not the storm’s absolute intensity, but how a relatively common system managed to produce such significant surface impacts.
One of the most studied mechanisms in the context of climate change is the modification of the polar jet stream—a high-altitude band of strong winds that separates cold polar air from warmer mid-latitude air. The accelerated warming of the Arctic, driven by sea ice melt, is weakening this thermal gradient, leading to a more wavy, slower, and at times stationary jet stream. These meanders increase the likelihood of persistent weather patterns and stronger contrasts between air masses. The position of the Azores High is closely linked to this dynamic: when upper-level circulation changes, the high tends to shift southward or weaken, diminishing its usual role in deflecting Atlantic depressions. This combination creates a more favorable context for the prolonged presence of low-pressure systems over Portugal, increasing the frequency and persistence of rainfall and wind events.
The impact of these changes is not the creation of new types of storms, but rather the alteration of the conditions in which they develop. Familiar systems now evolve in environments more conducive to amplifying their impacts—whether through longer duration, less predictable trajectories, or interactions with increasingly contrasting air masses.
In Kristin’s case, the synoptic configuration combined a marked pressure gradient, an active cold front, and a vigorous atmospheric circulation associated with the advection of colder air at altitude. This combination strengthened wind and precipitation, especially in specific sectors of the depression. The strongest winds occurred in the southern and southwestern sectors, near the cold front and in the forward-right quadrant of the low-pressure center, where the pressure gradient was steepest. The system’s shallow structure contributed to wind concentration in specific areas, while local factors such as topography and wind exposure further modulated surface intensity.
None of this is anomalous when considered in isolation. What is changing is the frequency of these efficient atmospheric combinations. It cannot be claimed that Storm Kristin was caused by climate change. However, it is accurate to state that global warming is altering large-scale atmospheric circulation and increasing the likelihood of meteorological phenomena producing more severe impacts.
Climate change acts as an amplifier. It does not create the storm, but it sets the stage for relatively ordinary systems to evolve and generate significant effects. The climate signal is global and persistent; the meteorological phenomenon is local and immediate. Kristin’s efficiency was unique—and that uniqueness is what, in a changing climate context, becomes increasingly relevant.
Alexandra Monteiro, Alfredo Rocha, David Carvalho, Susana Pereira (Alphabetical order)
members of the Research Cluster 3, CESAM