Do you need to know, when is the best time to go to Puerto Rico? Then you should take a look here, what weather you can expect there during the year.
The climate of Puerto Rico is tropical marine. You can expect warm or hot weather and little seasonal variations of temperature. Weather is usually significantly colder in mountains than on the lowlands. The rainy season is from April to November.
When speaking about the usual weather in this state, the information is relevant for example for these popular places: Aguadilla, Arecibo, Añasco, Caguas, Camuy, Carolina, Culebra, Dorado, Eastern Coast, El Yunque National Forest, Fajardo, Guánica, Isabela, La Montaña, La Parguera, Loiza, Luquillo, Mayagüez, Moca, Naguabo, Northern Coast, Ponce, Porta Caribe, Porta del Sol, Rincón, Rio Grande, San Germán, San Juan, Vieques.
Let's look now what weather you can expect here. (Warning: As we don't have reliable data for this country, we use data from nearby locations for these statistics.) The warmest month here is August, the average maximum temperature is 32.6 ℃ (90.68 ℉). The average minimum temperature in this month is 25.6 ℃ (78.08 ℉). The coldest month here is January, the average maximum temperature is 28.1 ℃ (82.58 ℉). The average minimum temperature in this month is 22.3 ℃ (72.14 ℉). The most rainy month here is November, the average number of rainy days is 20. The least rainy month here is March, the average number of rainy days is 12.2. 
When travelling to some places in Puerto Rico, always consider the altitude of the the place as well. The highest point here is Cerro de Punta (1338 m) and the lowest point is Caribbean Sea (0 m). So the differences in altitudes in this country are not negligible and you should expect the weather to be different in places in different altitudes. Keep in mind, that the temperature usually decreases by 1.2 - 1.9 ℃ (2.2 - 3.5 ℉) per 200 m (656 ft), depending on the other conditions. (And we should add, that in the very special condition named thermal inversion even the temperature may be higher in higher altitudes.)
Typical (usual) weather in Puerto Rico in January is this: The average highest temperature in Puerto Rico in January is 28.1 ℃ (82.58 ℉). The average lowest temperature is 22.3 ℃ (72.14 ℉). At the beginning of January you can expect higher temperatures, the average highest temperature is around 28.2 ℃ (82.76 ℉). At the end of January you can expect higher temperatures, the average highest temperature is around 28.85 ℃ (83.93 ℉). The average number of rainy days in January is 18. The average rainfall is 93.4 mm (look here, what this number means). When planning your travel, please, keep in mind, that actual weather may differ from these average values. The length of the day at the beginning of this month is approximately 11:02 (hours and minutes), in the middle of the month 11:08 and at the end of the month 11:18.This data is approximate because we do not have exact data for this country. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Puerto Rico in February is this: The average highest temperature in Puerto Rico in February is 29.6 ℃ (85.28 ℉). The average lowest temperature is 22.2 ℃ (71.96 ℉). At the beginning of February you can expect lower temperatures, the average highest temperature is around 28.85 ℃ (83.93 ℉). At the end of February you can expect higher temperatures, the average highest temperature is around 29.65 ℃ (85.37 ℉). The average number of rainy days in February is 13.7. The average rainfall is 59.5 mm (look here, what this number means). When planning your travel, please, keep in mind, that actual weather may differ from these average values. The length of the day at the beginning of this month is approximately 11:18 (hours and minutes), in the middle of the month 11:32 and at the end of the month 11:46.This data is approximate because we do not have exact data for this country. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Puerto Rico in March is this: The average highest temperature in Puerto Rico in March is 29.7 ℃ (85.46 ℉). The average lowest temperature is 23 ℃ (73.4 ℉). At the beginning of March you can expect lower temperatures, the average highest temperature is around 29.65 ℃ (85.37 ℉). At the end of March you can expect higher temperatures, the average highest temperature is around 30.15 ℃ (86.27 ℉). The average number of rainy days in March is 12.2. The average rainfall is 50 mm (look here, what this number means). When planning your travel, please, keep in mind, that actual weather may differ from these average values. The length of the day at the beginning of this month is approximately 11:46 (hours and minutes), in the middle of the month 12:02 and at the end of the month 12:18.This data is approximate because we do not have exact data for this country. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Puerto Rico in April is this: The average highest temperature in Puerto Rico in April is 30.6 ℃ (87.08 ℉). The average lowest temperature is 24.2 ℃ (75.56 ℉). At the beginning of April you can expect lower temperatures, the average highest temperature is around 30.15 ℃ (86.27 ℉). At the end of April you can expect higher temperatures, the average highest temperature is around 31 ℃ (87.8 ℉). The average number of rainy days in April is 13.1. The average rainfall is 117.4 mm (look here, what this number means). When planning your travel, please, keep in mind, that actual weather may differ from these average values. The length of the day at the beginning of this month is approximately 12:18 (hours and minutes), in the middle of the month 12:33 and at the end of the month 12:47.This data is approximate because we do not have exact data for this country. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Puerto Rico in May is this: The average highest temperature in Puerto Rico in May is 31.4 ℃ (88.52 ℉). The average lowest temperature is 24.7 ℃ (76.46 ℉). At the beginning of May you can expect lower temperatures, the average highest temperature is around 31 ℃ (87.8 ℉). At the end of May you can expect higher temperatures, the average highest temperature is around 31.75 ℃ (89.15 ℉). The average number of rainy days in May is 15.6. The average rainfall is 148.6 mm (look here, what this number means). When planning your travel, please, keep in mind, that actual weather may differ from these average values. The length of the day at the beginning of this month is approximately 12:47 (hours and minutes), in the middle of the month 12:59 and at the end of the month 13:08.This data is approximate because we do not have exact data for this country. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Puerto Rico in June is this: The average highest temperature in Puerto Rico in June is 32.1 ℃ (89.78 ℉). The average lowest temperature is 25.4 ℃ (77.72 ℉). At the beginning of June you can expect lower temperatures, the average highest temperature is around 31.75 ℃ (89.15 ℉). At the end of June you can expect lower temperatures, the average highest temperature is around 31.9 ℃ (89.42 ℉). The average number of rainy days in June is 14.2. The average rainfall is 110.2 mm (look here, what this number means). When planning your travel, please, keep in mind, that actual weather may differ from these average values. The length of the day at the beginning of this month is approximately 13:08 (hours and minutes), in the middle of the month 13:13 and at the end of the month 13:13.This data is approximate because we do not have exact data for this country. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Puerto Rico in July is this: The average highest temperature in Puerto Rico in July is 31.7 ℃ (89.06 ℉). The average lowest temperature is 25.5 ℃ (77.9 ℉). At the beginning of July you can expect higher temperatures, the average highest temperature is around 31.9 ℃ (89.42 ℉). At the end of July you can expect higher temperatures, the average highest temperature is around 32.15 ℃ (89.87 ℉). The average number of rainy days in July is 18.6. The average rainfall is 127.8 mm (look here, what this number means). When planning your travel, please, keep in mind, that actual weather may differ from these average values. The length of the day at the beginning of this month is approximately 13:13 (hours and minutes), in the middle of the month 13:08 and at the end of the month 12:59.This data is approximate because we do not have exact data for this country. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Puerto Rico in August is this: The average highest temperature in Puerto Rico in August is 32.6 ℃ (90.68 ℉). The average lowest temperature is 25.6 ℃ (78.08 ℉). At the beginning of August you can expect lower temperatures, the average highest temperature is around 32.15 ℃ (89.87 ℉). At the end of August you can expect lower temperatures, the average highest temperature is around 32.5 ℃ (90.5 ℉). The average number of rainy days in August is 18.3. The average rainfall is 141.1 mm (look here, what this number means). When planning your travel, please, keep in mind, that actual weather may differ from these average values. The length of the day at the beginning of this month is approximately 12:59 (hours and minutes), in the middle of the month 12:47 and at the end of the month 12:33.This data is approximate because we do not have exact data for this country. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Puerto Rico in September is this: The average highest temperature in Puerto Rico in September is 32.4 ℃ (90.32 ℉). The average lowest temperature is 25 ℃ (77 ℉). At the beginning of September you can expect higher temperatures, the average highest temperature is around 32.5 ℃ (90.5 ℉). At the end of September you can expect lower temperatures, the average highest temperature is around 31.7 ℃ (89.06 ℉). The average number of rainy days in September is 17.8. The average rainfall is 150 mm (look here, what this number means). When planning your travel, please, keep in mind, that actual weather may differ from these average values. The length of the day at the beginning of this month is approximately 12:33 (hours and minutes), in the middle of the month 12:18 and at the end of the month 12:02.This data is approximate because we do not have exact data for this country. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Puerto Rico in October is this: The average highest temperature in Puerto Rico in October is 31 ℃ (87.8 ℉). The average lowest temperature is 24.7 ℃ (76.46 ℉). At the beginning of October you can expect higher temperatures, the average highest temperature is around 31.7 ℃ (89.06 ℉). At the end of October you can expect lower temperatures, the average highest temperature is around 30.55 ℃ (86.99 ℉). The average number of rainy days in October is 17.8. The average rainfall is 142.6 mm (look here, what this number means). When planning your travel, please, keep in mind, that actual weather may differ from these average values. The length of the day at the beginning of this month is approximately 12:02 (hours and minutes), in the middle of the month 11:47 and at the end of the month 11:32.This data is approximate because we do not have exact data for this country. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Puerto Rico in November is this: The average highest temperature in Puerto Rico in November is 30.1 ℃ (86.18 ℉). The average lowest temperature is 24 ℃ (75.2 ℉). At the beginning of November you can expect higher temperatures, the average highest temperature is around 30.55 ℃ (86.99 ℉). At the end of November you can expect lower temperatures, the average highest temperature is around 29.2 ℃ (84.56 ℉). The average number of rainy days in November is 20. The average rainfall is 163.8 mm (look here, what this number means). When planning your travel, please, keep in mind, that actual weather may differ from these average values. The length of the day at the beginning of this month is approximately 11:32 (hours and minutes), in the middle of the month 11:19 and at the end of the month 11:08.This data is approximate because we do not have exact data for this country. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Puerto Rico in December is this: The average highest temperature in Puerto Rico in December is 28.3 ℃ (82.94 ℉). The average lowest temperature is 22.6 ℃ (72.68 ℉). At the beginning of December you can expect higher temperatures, the average highest temperature is around 29.2 ℃ (84.56 ℉). At the end of December you can expect lower temperatures, the average highest temperature is around 28.2 ℃ (82.76 ℉). The average number of rainy days in December is 19.5. The average rainfall is 129.3 mm (look here, what this number means). When planning your travel, please, keep in mind, that actual weather may differ from these average values. The length of the day at the beginning of this month is approximately 11:08 (hours and minutes), in the middle of the month 11:02 and at the end of the month 11:01.This data is approximate because we do not have exact data for this country. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.