Your 2014 Brazil World Cup Weather Guide

Brazilian fansWith less than two weeks to go to the start of the tournament maybe it’s time to look at how the weather may affect the players, especially those from more temperate climes. Much has been said about the effect that high temperatures and humidity will have, but in some cases it may not be as bad as some might think, especially for evening kick-offs. Still, it is a handy excuse to have at the ready if the result of the match goes the wrong way!

Brazil is a huge country, and therefore climate varies from region to region. The host city nearest to the equator is Manaus (3 ° South, altitude 80 metres, in the rainforest), and is the location of England’s first match against Italy on June 14th (1800 local time). The city furthest south is Porto Alegre (30 ° South, altitude 3 metres) and hosts France-Honduras as its first match on June 15th (16:00 local time). In between these two latitudes there are ten more cities, some at altitude, others along the coast. All cities are 4 hours behind Irish time (3 behind GMT), except Manaus, which is 5 hours behind (4 behind GMT).

Cities

First, let’s look at humidity. Air contains water in the form of a gas (vapour). The amount of this vapour varies widely from place to place and season to season, with higher values obviously occuring in equatorial regions. Warm air can hold a lot more vapour than cold air. Dewpoint (°C) is the temperature to which air of a certain water vapour-loading needs to be cooled for condensation of the vapour to liquid water to occur (fog, cloud, etc.). The more humid the air, the higher the dewpoint, and vice versa. Dewpoint can tell us the exact amount of water vapour in the air, the Mixing ratio, which is expressed as grams of water vapour per kg of air (g/kg). In standard conditions, a dewpoint of 24 °C gives a mixing ratio of 18.8 g/kg, whereas 10 °C gives just 7.6 g/kg (see below).

Dewpoint and Mixing Ratio
Dewpoint and corresponding Mixing Ratio, at sea level.

Dewpoint is always reported along with temperature in weather reports, and this allows the Relative Humidity to be calculated. Relative Humidity (expressed as a percentage) is the amount of water vapour contained in the air compared to the maximum amount possible for that temperature. Relative humidity of 100% means that the air is saturated and can hold no more vapour, so any cooling or addition of vapour to it will lead to condensation. Air of any temperature can have a R.H. of 100%, be it at -30 or +30 °C, but people usually only refer to high R.H. levels when talking about hot air, as this is where the humidity is felt the most.

The human body’s temperature is around 37 °C, with a skin-temperature of around 33 °C. The body regulates its temperature through an ingenious system of sweat glands on the skin. When these glands secrete sweat onto the surface of the skin, the energy required to evaporate this sweat is taken from the skin, cooling it slightly. If the air is dry, this evaporation process is very efficient, but in humid air it is much less so because the air is already close to saturation.

Let’s look at Manaus, as it is the focus of England’s preparations. It is a list of the daily reports from the airport for June-July last year. Clicking on each day will show the individual 6-hourly reports, with the dewpoint shown as Td. We can see that the weather is very stable from day to day, typical of an Equatorial climate. The temperature and humidity do not show much variation, with maximum temperatures always around 30-32 °C and dewpoint temperatures always around 23-24 °C. The only real variable is the cloud cover and precipitation, which can range from partly cloudy to torrential downpours.

For Manaus at its hottest part of the day (say 32 °C and dewpoint 24 °C) the relative humidity is around 62% (see this handy calculator). At its coolest part of the day (around dawn, temperature and dewpoint 24 °C) the relative humidity is obviously around 100%. I have heard some media outlets saying that afternoon matches would be played in 100% R.H., which is obviously incorrect, as for that to occur we would need a dewpoint of 32 °C, something that is extremely rare in equatorial regions. With England’s first match at 1800 local time (2300 UTC), the temperature should be around 27 °C and 83% R.H. Still pretty muggy but not quite as bad as some might think.

Porto Alegre shows a different story, with maximum temperatures varying from the teens to upper 20s and dewpoints in the teens. This should pose no problem for most teams as it is typical of the climate of most Eurpoean countries at this time of the year. Curitiba and São Paulo, just north of Porto Alegre, show a cooler climate, being at over 900 m and 800 m, respectively. Farther east, Rio de Janeiro reaches the high 20s but dewpoints remain below 20 °C.

Along the northeast and east coast are the cities of Fortaleza, Recife, Natal and Salvador. Although farther north, their proximity to the Atlantic Ocean means that the sea breeze limits maximum temperatures to around 25-30 °C and dewpoints around 20 °C or below.

The remaining three cities of Cuiabá, Brasília and Belo Horizonte are located inland and at varying altitudes. Cuiabá, in the far west of the country, is at an altitude of around 190 metres, and temperatures and dewpoints rise to the low 30s and low 20s, respectively. Located much higher, Belo Horizonte (830 m) and Brasília (1060 m) offer some refreshing respite, with temperatures in the 20s and dewpoints in the teens. Evenings get cooler, especially in Brasília.

Of course it’s one thing taking values from an official weather station, which is well ventilated, but it’s another thing being enclosed inside a packed stadium. For the evening kick-offs it’s not much of an issue, but as some games kick off at 1300 local time, temperature will be a factor. Obviously this is where some nationalities will have an advantage, and with England’s final group game against Costa Rica at 1300 in Belo Horizonte, how much of the scoreline will conditions dictate? We’ll just have to sweat it out and see.

Full list of fixtures.

Latest satellite animation.

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