Map from Google - Kuwait

Kuwait has a subtropical desert climate, with mild winters and very hot summers. The sun usually shines all year round.
Rainfall, slightly higher than 40 inches per year, occurs mainly from November to April, in the form of heavy showers, which can sometimes be so intense and concentrated as to cause flooding.
Here is the average precipitation in Kuwait City.
Average precipitation - Kuwait City
Kuwait CityJanFebMarAprMayJunJulAugSepOctNovDecYear
Kuwait CityJFMAMJJASONDY
Prec. (in)1.20.60.60.60.600000.20.815.5
Days65542000014532

Winter from December to February is mild: the average temperature in January is 55 degrees Fahrenheit. The nights are cool, on average about 46/48 °F, but sometimes the temperature can drop to 32 °F. The days are mild or pleasantly warm, around 65 °F in January and 68/70 °F in December and February, but with peaks of 81/86 °F when the wind blows from the south. In winter the sun often shines, but some cloudy days also possible, even with some rain.
In spring, the prevailing weather is nice and sunny; the temperature rises rapidly, and already in April highs are around 86 °F. The winds from the Arabian desert can raise the temperature and bring sandstorms: as early as April it can exceed 105 °F, and in May even 113 °F.
Summer in Kuwait is scorchingly hot and windy; the prevailing winds blow from the inland desert, therefore the influence of the sea is minimal. From June to August, the temperature is normally around 111/115 °F, and sometimes it remains around 85 °F even at night. High-temperature records are around 126/127 °F. The humidity is very low (it often falls below 10%), and combined with the wind, it can cause dehydration and heat strokes. Fortunately, public buildings and hotels are equipped with air conditioning.
The small island of Failaka is usually torrid as well as the mainland, because it receives winds from the continent, but sometimes it can be stifling, especially in September and October, in the days when the wind calms down a bit.
In autumn, it's still hot and sunny in October, while during the month of November the temperature drops below 85 °F.
Here are the average temperatures of Kuwait City.
Average temperatures - Kuwait City
Kuwait CityJanFebMarAprMayJunJulAugSepOctNovDec
Kuwait CityJFMAMJJASOND
Min (°F)464855667582868477685748
Max (°F)64707990102111115113108978168

The Persian Gulf in the northern part is very cool for swimming in winter, it becomes warm enough in May, while in summer it's very warm, exceeding 85 °F for a few months.
Sea temperature - Kuwait
KuwaitJanFebMarAprMayJunJulAugSepOctNovDec
KuwaitJFMAMJJASOND
Sea (°F)666364707984889088847972

Kuwait

When to go

The best time to visit Kuwait runs from mid-November to mid-March. In winter, from December to February it can sometimes get cold at night, and there can be some rain, but at least you avoid the scorching heat. On early November and at late March sometimes it can be hot. However, in Kuwait, the heat is almost always torrid and not humid, so it is more bearable than in other countries of the Persian Gulf; the important thing is to drink a lot and to be protected from the sun.

What to pack

In winter: spring/autumn clothes, t-shirt or shirt for warm days, sweater and warm jacket for the evening and cold days, scarf for the wind, possibly an umbrella.
In summer: lightweight, loose fitting clothes, made of natural fabric (cotton or linen), desert turban, sweater and scarf for air conditioned places. For women, it is best to avoid shorts and miniskirts outside tourist resorts.
For the reef, equipment for snorkeling, water shoes or rubber soled shoes.