August Jamaica falls within the island's summer and rainy season, so you can expect warm, humid weather with a chance of thunderstorms. Daytime temperatures Highs average around 89°F (32°C). It rarely falls below 87°F (31°C) or exceeds 91°F (33°C). Nighttime temperatures Lows average around 78°F (26°C). It rarely falls below 76°F (24°C) or exceeds 81°F (27°C). Humidity Expect high humidity levels throughout the day and night. The chance of muggy conditions is virtually constant during August, hovering around 100%.