Map from Google - Dubai

The climate of Dubai, the most populous of the United Arab Emirates, is subtropical desert, with very mild or pleasantly warm winters, and scorchingly hot summers, in which the combination of temperature and humidity makes the heat really oppressive. In fact, in summer the wind usually blows directly from the sea, bringing moisture from the Persian Gulf.

The average temperature goes from 18.5 °C (65 °F) in January, to 35.5 °C (96 °F) in August.
Here are the average temperatures.
Average temperatures - Dubai
DubaiJanFebMarAprMayJunJulAugSepOctNovDec
DubaiJFMAMJJASOND
Min (°C)141517202426283027231916
Max (°C)232427323738404138353126
Min (°F)575963687579828681736661
Max (°F)7375819099100104106100958879

Precipitation is poor, and amounts to 100 millimetres (4 inches) per year; most of the rainfall occurs from December to March or April. The rains usually occur in the form of showers, brief but intense. In summer it never rains.
Here is the average precipitation.
Average precipitation - Dubai
DubaiJanFebMarAprMayJunJulAugSepOctNovDecYear
DubaiJFMAMJJASONDY
Prec. (mm)1035251010000021598
Prec. (in)0.41.410.40000000.10.63.9
Days24420000000214

Every so often, during winter, from December to February, and more rarely in March, there can be some cool days, with lows around 10 °C (50 °F), and highs around 20 °C (68 °F).

However, when the southerly winds blow, in winter the temperature can get close to 30 °C (86 °F), while in spring and autumn, ie already in April and still in November, it can touch 40 °C (104 °F). In summer it goes obviously even worse: in July and August the temperature can touch 47/48 °C (117/118 °F). However, on the positive side, when the wind blows from the south, ie from the Arabian Desert, relative humidity decreases.

Wind is often lively. In winter and spring there may be strong winds, from February to April, but sometimes this can happen also in summer. The wind can raise storms of sand and dust.

The amount of sunshine in Dubai is great all year round: blue skies are the norm, however, from December to March some cloud banks can pass, which can sometimes produce some showers, while in summer there can be some cloudiness related to the monsoon of southern Arabia, which here produces very little effect.

Dubai

The sea in Dubai is warm enough for swimming all year round, although from January to March the water temperature drops to 23 °C (73 °F). In summer, the Persian Gulf is one of the warmest seas in the world, and exceeds 30 °C (86 °F) from June to October, so it allows long swims.
Here are the average sea temperatures.
Sea temperature - Dubai
DubaiJanFebMarAprMayJunJulAugSepOctNovDec
DubaiJFMAMJJASOND
Sea (°C)232323252931323332312825
Sea (°F)737373778488909190888277

When to go

The best time to visit Dubai goes from December to February, to avoid the heat that dominates for many months a year.
During summer, the heat is so intense that it can be uncomfortable even to stay under the umbrella. Usually in winter the air temperature allows to sunbathe, except in the coolest days. Hence, the best months for swimming and sun bathing are March and November, although in the first part of March, sometimes it can be cool or a little cold, in the evening and at night, and in any case in March the sea is less warm than in November. In April, some days are acceptable, at other times the temperature can already reach 40 °C (104 °F).
Fortunately, public buildings and hotels are equipped with air conditioning.