Why does the UAE get so humid without rain? The science explained

Dubai: Few weather phenomena puzzle UAE residents more than summer humidity. Some days the air feels almost impossible to breathe; humidity readings climb above 90 per cent, yet the skies remain cloudless and not a drop of rain falls.

So where does all that moisture come from? Why doesn't it become rain? And what does a humidity reading of 60 per cent actually mean?

Meteorologists say the answer lies in how moisture moves through the atmosphere rather than how much of it is present.

"Humidity alone does not produce rain," Ibrahim Al Jarwan, Chairman of the Emirates Astronomical Society, and a member of the Arab Union for Astronomy and Space Sciences, told Gulf News.

Rain requires moist air to rise high into the atmosphere, cool and condense into clouds before droplets become heavy enough to fall. During much of the UAE's summer, those conditions are often absent.

Where does the humidity come from?

Contrary to what many people assume, the Arabian Gulf is not always the main source of the country's summer humidity.

According to Al Jarwan, the most significant increase in humidity from August onwards is driven by "Kous" winds carrying moisture from the Arabian Sea and the Gulf of Oman.

These south-easterly winds spread humid air across much of the country, pushing humidity levels above 90 per cent on some days.

The same weather pattern also helps generate towering convective clouds over the Hajar Mountains, sometimes bringing heavy thunderstorms to mountainous areas and the gravel plains stretching between Al Ain and Al Dhaid. It can also produce low clouds and light drizzle over parts of the east coast.

The Arabian Gulf still plays an important role, particularly along the coast. Warm sea temperatures cause large amounts of water to evaporate, adding moisture to the air over cities including Dubai, Abu Dhabi, Sharjah and Ajman. Humidity can also increase after rainfall, as water evaporates back into the atmosphere.

Why doesn't all that moisture become rain?

High humidity simply means there is plenty of water vapour in the air. Rain, however, requires something more: the air must rise.

When moist air rises, it cools. As temperatures fall, the air can no longer hold the same amount of water vapour, causing tiny droplets to form clouds.

During much of the UAE's summer, the atmosphere is relatively stable, limiting large-scale upward motion across much of the country. As a result, moisture remains trapped in the lower atmosphere, making conditions feel hot and oppressive without necessarily producing rainfall.

Rain is more likely where mountains force humid air upwards, explaining why summer thunderstorms are usually confined to eastern and mountainous parts of the UAE.

Why do Dubai and Abu Dhabi feel more humid than inland deserts?

One reason summer weather feels very different in Dubai and Abu Dhabi than it does in Al Ain or the Empty Quarter is their proximity to the sea.

Coastal cities sit next to large bodies of warm water that constantly release water vapour into the atmosphere through evaporation.

Even when moisture arriving from the Arabian Sea and Gulf of Oman is driving the UAE's broader humidity pattern, the Arabian Gulf remains an important local source of moisture for coastal areas.

As sea breezes develop, this moist marine air is carried inland, raising humidity levels along much of the UAE's coastline.

By contrast, inland desert areas are farther from these marine moisture sources. They often record higher daytime temperatures but lower humidity, which is why the heat in places such as Al Ain typically feels drier than in Dubai or Abu Dhabi.

The difference becomes even more noticeable after sunset. Coastal areas retain abundant moisture from the sea, while inland locations cool more rapidly overnight. This helps explain why inland regions frequently experience early morning fog, even though coastal cities generally remain more humid overall.

What exactly is humidity?

Humidity is simply the amount of water vapour present in the air. The figure shown in weather forecasts is usually relative humidity, which compares how much moisture the air currently contains with the maximum amount it could hold at its current temperature.

A reading of 60 per cent does not mean that 60 per cent of the air is made up of water.

Instead, it means the air is holding 60 per cent of the maximum water vapour it could contain at that particular temperature.

Meteorologists often compare it to a sponge. Warm air behaves like a larger sponge, capable of holding far more water than cold air.

That is why 60 per cent humidity at 40°C contains significantly more moisture than 60 per cent humidity at 20°C, even though the percentage is identical.

Why does 60 per cent humidity feel different in summer than in winter?

One of the biggest misconceptions is that 60 per cent humidity always feels the same. It doesn't.

Relative humidity is measured against the maximum amount of water vapour the air can hold at its current temperature.

Warm air can hold far more water vapour than cool air.

For example, air at 40°C can hold more than three times as much water vapour as air at 20°C before becoming saturated. That means a relative humidity reading of 60 per cent at 40°C contains substantially more moisture than 60 per cent at 20°C, even though the percentage is identical.

That is why a summer day in Dubai with temperatures above 40°C and humidity of around 60 per cent often feels far more oppressive than a winter day with the same humidity reading.

The extra moisture also makes it harder for sweat to evaporate from the skin, reducing the body's natural cooling mechanism and making conditions feel considerably hotter than the thermometer suggests.

Why does humidity rise at night?

One of the UAE's most noticeable weather patterns occurs after sunset.

As temperatures fall overnight, the amount of water vapour in the air changes very little. Cooler air, however, cannot hold as much moisture as warmer air, causing relative humidity to increase.

This is why humidity often reaches 90 to 100 per cent before sunrise.

If temperatures fall to the dew point, the temperature at which the air becomes saturated; water vapour begins condensing into tiny droplets. Depending on conditions, this produces dew on surfaces or fog close to the ground, particularly across inland areas where night-time cooling is faster than along the coast.

Al Jarwan said fog becomes increasingly common from mid-August onwards as humidity spreads deeper into inland areas during calm nights. While fog can occur at different times of the year, it is most frequent from mid-September to mid-November, with October among the peak months.

Why does the weather feel so uncomfortable?

Humidity affects how efficiently the body cools itself. Normally, sweat evaporates from the skin, removing heat from the body. But when humidity is high, evaporation slows dramatically.

The result is that people feel much hotter than the actual air temperature, even if the thermometer has not changed.

That is why August and September are widely regarded as the UAE's most uncomfortable months, combining extreme heat with exceptionally high humidity.