Outlook: Why the weather is going crazy in the 2023 season
It all began many weeks ago: It is 2 April 2023 and after a long and wet period, a high pressure system called "Nadine" appears on the weather charts. It moves from the Azores towards the European mainland. Just one day later, a so-called high pressure bridge forms between the Azores high and a newly formed Scandinavian high. This formation blocks the Atlantic low-pressure motorway. As a result, the phalanx of alternating weather systems that are otherwise common in our latitudes is suddenly interrupted. This is not an everyday occurrence. However, what is happening in the atmosphere at this time is not particularly unusual either. But that is about to change.
In April, nobody suspects that this newly formed high-pressure situation will remain more or less pronounced for many weeks, well into June. Many parts of Europe come under the influence of lower air pressure in April or May, along with the associated precipitation. At the same time, however, an often strong high has been permanently present on European weather maps since then.
Air masses arrive unchecked
Its position varies, which in turn has an impact on the weather parameters. Its position over the British Isles shifts air masses from the far north to the North Sea and Baltic Sea regions. As winds in the northern hemisphere rotate clockwise around a high, these air masses come unchecked from the regions around northern Norway and Svalbard. This means that the air flowing over the North Sea cools down so much, especially at night, that sea or high fog forms, which is only gradually lifted by the sun the following afternoon.
This means that temperatures on the North Frisian Islands only reach a maximum of twelve degrees Celsius. On the other hand, Denmark and Schleswig-Holstein serve as a heat buffer for the Baltic Sea. Even if the water temperatures are initially similar, the air coming from Norway is heated so much over the already warm land that fog forms much less frequently on the Baltic Sea.
The sun comes out much earlier here and the air temperatures climb well above 20 degrees in some places - while the sailors on Sylt are sitting in thick jackets in the cockpit at the same time.
Consequential weather change
As already mentioned, the high pressure system does not stay in one place; it sometimes moves over to Scandinavia. In the past few weeks, the seas bordering northern Germany have suddenly moved to the southern side of the pressure pattern. As a result, the wind shifts back to an easterly direction. This means that the heat barrier for the Baltic Sea is no longer in effect and is now affecting the Elbe and North Sea instead. The onshore wind cools the coastal regions between Rügen and Flensburg, whereas sailors in the North Sea area are exposed to the warmer air masses from the land and suddenly start sweating on board on a downwind course at up to 28 degrees.
This interplay of wind and air masses reflects the oscillation of the high. After the Scandinavian high, the Azores high often pushes directly back over the British Isles and forms a new system there, which then moves back over northern Europe. The effects are increasingly far-reaching from week to week and can be felt as far away as Central Europe. This is because the highs continue to expand with the seasonal warming of the northern hemisphere. Rain and lows, which occasionally show up again, become rarer. In many regions, there is a lack of precipitation for weeks until mid-June.
The crux: In contrast to the weather situation, the wind conditions are anything but permanent, i.e. constant. It's not just the wind direction that changes as the high moves. The pressure contrasts also increase and then decrease again. For example, one day in the western Baltic Sea there is only a light sea breeze of 3 Beaufort under the coast, while further out there is even a calm. And the next day, a harbour day is suddenly due, as 5 to 6, in gusts 7 to 8 Beaufort blow from the east.
All this, mind you, in pleasant temperatures and a bright blue sky! The abrupt change in weather or wind is not visibly announced. Only those who consult the weather maps know that the change in the position of the high will also result in a change in the wind. Even if the influence of the high on the atmosphere remains.
The effect of the sea breeze
Often there are additional lows that make their way from the Mediterranean to Poland and additionally fuel the opposing pressures of the easterly wind. If the effect of the sea wind is then added to the already strong wind, it is above all the strong gusts that push the sails properly without the usual cumulus clouds being visible. Invisible bubbles of warm air rise over the land. The resulting "air holes" are suddenly filled from the sea, so that it is always a little gustier for a short time.
Keyword Mediterranean: It also shows where the low-pressure areas are currently located. Because they haven't gone, they've just moved elsewhere. Such systems are also characterised by the fact that they usually have a cold body, i.e. they bring in cooler air masses from high altitudes. The huge and persistent high over the northern part of Europe has consequently deflected lower air pressure into the Mediterranean. And it is precisely there that we have higher temperatures on the ground and in the water due to the higher solar radiation.
If a depression forms here and brings cold air from higher up, both air masses exchange. The cold air is heavier and wants to go down. The warm air on the ground, which can absorb even more moisture, is displaced upwards. And it does so abruptly on the spot. This is how the mighty cumulonimbus clouds with heavy rain and thunderstorms form.
Hardly any pressure contrasts to be found
As we can almost speak of a low-pressure trough over the entire Mediterranean in recent weeks, there are hardly any pressure contrasts to be found here. For this reason, there are also no high-altitude winds to carry the thunderstorm cells away. They remain stationary and unfold their full potential at one point. The extra water vapour in the air is released abruptly. This explains the flooding in Italy, Mallorca and Barcelona, to name just a few of the regions affected by bad weather.
As the sun is also a key driver for this, heating up the air masses in the lower layers, you can set the clock for when thunderstorms will form again. Every day, the thunderstorm radar sees hardly anything conspicuous in the morning, but in the afternoon it is suddenly filled with lightning. This situation was repeated day after day. Mostly over land, rarely over water. Only a few cells drifted out to sea.
At least there has been some dynamism over Morocco recently: stronger lows may form at times near the Atlas Mountains, which will not only make the weather between the Balearic Islands and Zadar a little more extreme than it already is due to the local cells caused by the diurnal cycle. These lows also find their way as far as Poland. But it won't go any further, as the highs are still blocking the way here. However, it is precisely these lows that cause the easterly wind in the Baltic Sea to rise to 5 or 6 Beaufort.
The circle is complete, or ...
So you might think that the weather has come full circle. But let's take another look at the Atlantic. Our high pressure situation usually originates from the Azores High. Due to the routings of many sailors who have travelled and are still travelling back to Europe from the Caribbean, the picture here is also very different at times: the high is often very extended and for a very long time. For a few days, you can only see one huge area of high pressure across the entire North Atlantic. Not a low far and wide. They do exist, they are usually quite intense, and the Azores and Canary Islands in particular have been hit harder. However, their number is significantly lower than in previous years.
As a result, there is a lack of wind to propel the sailors on their way home and also to circulate the seas and bring up fresher deep water. Especially along the trade winds, the water temperatures are now much higher than usual at this time of year.
In addition to the African coast, this can also be seen massively off the British coast. This is not surprising, as there was a frequent and long-lasting high here. The sun was able to warm the water completely undisturbed. Off the African coast and also on the open Atlantic, however, other effects are also assumed: Either the trade winds are also weak due to the strongly extended high. Or the lows over Morocco have disturbed the trade wind field off the coast in such a way that the winds have cancelled each other out and, as a result, water mixing in the Atlantic has also been prevented.
An additional warming effect can be the lack of Saharan dust. If the lows are not as strong and their path has changed, the trade winds are also weakened. This raises less dust, which is then carried out into the Atlantic. This dust acts as a natural shade provider. It does not allow as much sunlight through and thus ensures that the Atlantic does not overheat. Commercial shipping and the lower quantities of sulphur in fuel in recent years could also be another cause. If there are no sulphur particles in the atmosphere, which is to be welcomed from an ecological point of view, these molecules are no longer available to provide shade. More sunlight makes it through the layers of air to the water to warm it up.
Finally, the impending El Niño phenomenon may also have an impact on the weather and thus the temperature situation in the Atlantic. However, it is not entirely clear how large these effects are. Other effects are also just hypotheses to explain where this historically large increase in sea temperatures, especially in the Atlantic, comes from.
What will the weather be like during the season?
But how will the season continue if the weather patterns turn out to be so different from what we know from the past? Let's start with a somewhat simpler forecast: We are gradually entering the hurricane season. There will be hurricanes, and the first suspected zones have already been labelled by the NOAA (National Oceanic and Atmospheric Administration) at the level of Cape Verde. A few weeks ago, the NOAA also published forecasts predicting a moderate hurricane year, with only 12 to 17 such hurricanes. This also includes tropical storms that do not reach hurricane force with wind speeds of more than 188 km/h.
The number of genuine hurricanes should probably remain below ten. This sounds plausible, because in a year in which an El Niño builds up, slightly less hurricane activity can usually be expected. The wind circulation in the Pacific, where El Niño occurs, usually ensures stronger trade winds along the tropics and subtropics in the Atlantic. However, excessively high winds are counterproductive for the formation of a hurricane. During the initial swirling, they would prevent shearing and turning.
Example: Simply pull the plug in a full bathtub or sink, wait until the obligatory swirl forms and then blow vigorously into it. The vortex should dissolve.
It is therefore assumed that the number of tropical cyclones is normally high. Should any form, however, the higher water temperatures will come into play. Higher temperatures also mean more moisture in the atmosphere and therefore more energy available. The cyclones are therefore likely to increase significantly in intensity.
What this means for the North Sea and Baltic Sea
So what does this have to do with the weather systems over the North Sea and Baltic Sea and the forecast for the rest of the season? Quite a lot, actually. If hurricanes form, they usually follow the high winds and turn northwards near the Caribbean or the USA as soon as the Azores High becomes weak enough to allow this. If the storms are now stronger, this could have an impact as soon as they enter the extratropical low pressure zone of the mid-latitudes.
It is not uncommon to find names such as ex-"Sandy" or ex-"Mitch" on a weather map. These are tropical storms that hit Europe as normal lows. They are often the ones that end a previously long-lasting high pressure situation to herald a more changeable phase with more lows.
This year, however, it is to be feared that the tropical storms will maintain their strength for longer and hit Europe with considerably higher wind speeds. They draw their vital energy from the higher water temperatures. This explains why weakened hurricanes often intensify again in the very warm Gulf of Mexico.
Energetic weather
With the current deviations in water values around the British Isles, there is an increased risk that storms could pick up more energy there. There are therefore two potential scenarios for the rest of the season: either we see a persistent strong high in the haze around the North Sea and Baltic Sea, supported by the regular encroachment of the Azores High. So everything will stay the same. The wind will often be light. Only along the coasts will thermals provide sailable winds. Air and water temperatures will continue to rise. However, there will always be phases of low pressure in between, which will lose strength under the influence of the high pressure.
Only small disturbances originating from the lows will cause the odd heavy summer shower paired with thunderstorms. Low pressure systems that find their way northwards from the Mediterranean could then cause the often easterly gradient wind to increase again for a while.
Or a fundamental change in the weather is set in motion by a tropical storm. Due to the time of year, the strongest temperature differences between our latitudes and the Arctic are shifted further north. This is where we find our jet stream, which controls the underlying lows.
So, especially at the moment, with the very high temperatures extending far to the north, an initial spark is needed all the more. For example, in the form of a hurricane on the Atlantic! However, it is very uncertain whether and when this will come and change the situation.
This means that the first option is more likely: that the massive high over large parts of Europe will continue to be fuelled and continue to determine the weather patterns. Land and water masses will continue to heat up.
Sounds like a great season for sailors, just like in 2018, but on the other hand, this will increase the rain deficit in many parts of Europe. What's more, water temperatures of 24 degrees and above in the Baltic Sea, as in the Mediterranean, are not good for the ecosystems in the north.
You almost have to hope that a large low pressure complex will soon form near Iceland or even a hurricane, which will find its way to Europe in a weakened state and change this unusually stagnant high pressure situation back to one with westerly winds and rain. Even if the joy of sunny sailing days suffers a little as a result.
Sebastian Wache
