Miami Beach has a genuinely pleasant climate for most of the year. November through April is the prime tourist season: warm (22–28°C), dry, with low humidity and reliably clear skies. This is when the beaches are most enjoyable, hotels are fullest, and prices highest. Art Basel Miami Beach in early December marks the absolute peak, when the entire hospitality infrastructure is under pressure.
June through September is the hot and humid season, with temperatures consistently above 30°C and afternoon thunderstorms almost daily. The humidity is heavy but the water is warm for swimming, and the crowds are smaller (and prices lower). Hurricane season runs June through November; direct strikes on Miami Beach are rare but not impossible, and most of the famous storms pass to the south or north. The shoulder months of October and May are often excellent: warm, cheaper, and less crowded than winter.