Map from Google - Malta

Malta's climate is typically Mediterranean, with mild, rainy winters and hot, sunny summers.

Winter from December to February is mild: the average daily temperature in December is 57 °F, while that of January and February is 54 °F, and the daily temperature range is limited. Cold days are rare, and at most there may be some days with highs below 50 °F, but it never snows nor freezes. In this season, sunny periods are frequent, although there are even periods of a few days of bad weather, with rain and wind.

In spring, the temperature rises gradually: the average maximum is around 62 °F in March, 66 °F in April and 74 °F in May. The rains become less and less frequent, and as early as April they begin to be rare. The sun shines more and more unchallenged.

Summer, from June to August, is hot and sunny, with highs around 87 °F, but the heat is tempered by sea breezes.

In autumn, the temperature is initially high and then gradually decreases. In September the weather is still summer like, especially in the first half; usually at the end of the month there can be the first disturbances, accompanied by thunderstorms. In October, the temperature is still pleasant, with highs around 75/77 °F.
Here are the average temperatures.
Average temperatures - Valletta
Min (°F)484850545964707268635752
Max (°F)596163667382888882756863

Rainfall in Malta is not abundant: it slightly exceeds 20 inches per year. The rains follow the typical Mediterranean pattern, so they are concentrated in the period from October to March, while in the other months they are scarce, and in summer it almost never rains. Here is the average precipitation.
Average precipitation - Valletta
Prec. (in)

Sometimes the Maltese archipelago can be affected by the Sirocco, a hot dry wind blowing from the Saharan desert, often accompanied by dust or sand. When this wind blows, more frequently in spring and autumn, the temperature may rise by several degrees. On the contrary, in summer the Sirocco is usually brought by the African anticyclone, and blows weaker, in periods lasting a few days of very hot and sunny weather, with maximum temperatures about 100/105 °F.

La Valletta

The sea temperature is about 70 °F in June (therefore still a bit cool), 75 °F in July, 79 °F in August, and 77 °F in September.
Sea temperature - Valletta
Sea (°F)616159616470757977737064

When to go

The islands of the archipelago, with their characteristic towns, villages and ports, can be explored preferably in April, May and the first half of October.

For a beach vacation, the summer is the best season, from June to September.

What to pack

In winter: spring/autumn clothes, sweater, jacket, raincoat or umbrella.
In summer: light clothing, sunscreen, sun hat, light sweatshirt for the evening, light scarf for the sea breeze.