Malta has a Mediterranean climate. This means mild winters and warm or hot summers. Rain falls mostly in winter.
Most visitors mostly enjoy Malta's climate but often complain about the very hot summer (+35°C in July and August), the hot humid month of September and the cold humid months of December to February. Although the weather is generally very mild, if you are fussy then 6 months of the year might not suit you!
Malta enjoys over 3000 hours of sunshine a year making it one of the sunniest in Europe. For comparison, London has 37 sunshine hours in December whereas Malta has 161!
The sea is generally very enjoyable with temperatures ranging from 15-26°C