Shrouded in tropical rainforests and towering mountain ranges, Dominica is one of the most beautiful, natural islands in the Caribbean.
Because of its lush vegetation and high elevations, the Commonwealth of Dominica experiences some of the wettest weather in the Caribbean, creating a humid and tropical climate almost year-round. The variation in altitudes, along with the rain and heat, helps the island maintain diverse vegetation and plant life, including more than 1,000 species of flowering plants.
Average daytime temperatures on Dominica range from 75 degrees Fahrenheit up into the 80s. At nighttime, temperatures are a little cooler and drop about 10 degrees Fahrenheit. During the summer, island highs can reach way up into the 90s, with winter being only slightly cooler, averaging anywhere between 84 degrees Fahrenheit and 86 degrees Fahrenheit. The steamy temperatures are moderated by the cooling northeastern trade winds, which create a lovely island breeze providing relief from the sultry heat and humidity. December through May is the coolest and driest time of the year on the island and generally the best time to visit Dominica.
…the island does experience storm activity.
Seasons on the island aren’t determined so much by temperature as they are by rainfall. Dominica’s seasons are determined by the rainy and dry periods, though the island experiences wet weather consistently throughout the year. Cool rain showers occur almost every day, especially in Dominica’s heavily forested areas, but the dry season usually runs from January to May. The rainiest months are July through October, which are also the months that make up hurricane season.
Skies are usually more cloudy this time of year, and travelers can expect increased rainfall. Overall, Dominica gets about 350 inches of rain in the mountainous regions and about 40 inches on the western coast. Generally, visiting Dominica during the summer months is safe, but travelers should keep an eye on weather reports because the island does experience storm activity. And no matter what time of year you visit the island, always have a plan in case unexpected bad weather rears up.
Because different regions of the island differ in temperature as well as rainfall, vacationers should plan accordingly while visiting Dominica. If you intend to hike the trails of Dominica’s rainforests and mountainsides, be prepared for rain, which falls almost every day in the rainforest. It is a good idea to bring a rain jacket and other breathable rain gear in case of an unexpected shower or storm. Densely forested regions and high altitudes also tend to be cooler than coastal areas of the island, which are mostly hot and humid but tempered by sea breezes, so don’t forget to bring a jacket when exploring the mountains and forests.
(source: http://dominica-guide.info/weather/)