As is the case with many Caribbean islands, St. Lucia’s visitors should expect hot and humid weather conditions year round due to the island’s proximity to the equator. Fortunately, visitors will rarely feel uncomfortable as mild trade winds bring cool breezes off the water that offer some respite from the heat.
The average temperature in St. Lucia ranges from 70 degrees Fahrenheit to the upper 90s. Humidity on the island averages between 70 and 90 percent throughout the year. December through January are generally the coolest months with the temperatures being in the mid 70s to mid 80s in degrees Fahrenheit. The summer months of June through August are the hottest in St. Lucia where temperatures in the mid to upper 90s Fahrenheit are not uncommon.
Due to its location near the equator, St. Lucia does not have very well defined seasons. There is, however, a rainy season that generally falls between June and November. During this season, vacationers should be prepared for heavy, but sporadic showers that come on quickly. Visitors should not worry about traveling during the rainy season as the showers may come about rapidly, but blue skies are quick to follow.
…cool off on a hike…
Vacationers should be aware that there can be a great deal of variation in weather between the different regions of St. Lucia. If you are visiting one of the beaches around Castries orRodney Bay, expect temperatures to be high but not unbearable due to the cool breeze off the water. Visitors exploring one of the trails through the rain forest in the center of the island need to be prepared for some very hot and humid weather without any relief from the winds. Adventurous travelers can cool off on a hike to one of the Piton mountains, the distinguishing landscape feature of St. Lucia. Temperatures will drop significantly as the altitude increases and travelers may even want to bring along a light jacket to stay comfortable in the cool weather.
St. Lucia is located in the hurricane belt and it is possible for severe tropical storms to arise. The hurricane season is generally during the same time as the rainy season, June through November. Visitors should be cautious, but not deterred from visiting St. Lucia during this season. With advanced meteorological technology, storm prediction and detection will help prepare visitors and locals on the island for any potential danger. Visitors can take measures to protect themselves by researching weather conditions before traveling to St. Lucia and prepare accordingly.
(source: http://stlucia-guide.info/weather/)