Summer - festas, food and fireworks
Malta’s summers are sunny, hot and dry. You are most unlikely to get any rain and temperatures are generally in the high twenties, occasionally rising above 30ºC (86F). The sea gets warmer through the summer so it is at its warmest in late August/early September - but swimming is wonderful throughout the season and you will find the Maltese taking advantage all around the coast.
Summer is also festa time; each weekend throughout the summer one village or another (or maybe several) will host an exuberant celebration of their patron saint with the church lit up, the streets hung with bunting, processions, music, food and fireworks.
This is, of course, high season with the greatest numbers of tourists and the highest prices for accommodation.
Autumn - sunny and quieter than summer
It often remains hot and sunny through the autumn - I have sunbathed on October 30 on a wonderfully empty beach - but from mid-September there is a risk of winds and rain. Autumn is a good time for a trip combining sightseeing and the likelihood of sun. Walking, too, is very pleasant at this time of year, although this is also bird hunting season so in high coastal places you may come across men popping guns.
Winter - perfect for budget sightseeing
In winter it can still be warm and sunny (I’ve been too hot in a T-shirt in December). Even in January, the coldest month, average daytime temperatures are 9-14ºC. It can get chilly, though, especially when the wind blows.
This is the perfect time for sightseeing on a budget; accommodation costs can be less than half the August prices. Except, that is, over Christmas and New Year when Malta is covered in lights and nativity scenes and prices rise even though tourist numbers are still low.
Spring - wetter but green and beautiful
Spring is a little wetter and a lot greener than the rest of the year, and made colourful by wild flowers. Temperatures tend to be a bit lower than in the autumn too. This is the perfect time for walking and enjoying the landscape (especially on Gozo).