Do you need to know, when is the best time to go to Dominican Republic? Then you should take a look here, what weather you can expect there during the year.
The climate of Dominican Republic is tropical maritime. You can expect only little seasonal variation of temperature, but there is seasonal variation in rainfall. Hot wether is often moderated by winds and it is cooler in higher elevations. The rain season for the northern coast is from November to January, for the rest of the country the rain season is from May to November. 
When speaking about the usual weather in this state, the information is relevant for example for these popular places: Bahia de las Aguilas, Barahona, Bavaro, Bayahibe, Bonao, Cabarete, Eastern Cibao, Eastern Dominican Republic, Fondo Grande, Greater Santo Domingo, Higüey, Jarabacoa, Juan Dolio, La Romana, Las Galeras, Las Terrenas, Miches, Pedro Sánchez, Playa Bonita, Polo, Puerto Plata, Punta Cana, Rio San Juan, San Pedro de Macoris, Santa Barbara de Samana, Santiago de los Caballeros, Santo Domingo, Sosúa, Southern Dominican Republic, Western Cibao.
Let's look now what weather you can expect in the area around the capital and in many other cities. The warmest month here is August, the average maximum temperature is 32.1 ℃ (89.78 ℉). The average minimum temperature in this month is 23.2 ℃ (73.76 ℉). The coldest month here is January, the average maximum temperature is 28.7 ℃ (83.66 ℉). The average minimum temperature in this month is 20.3 ℃ (68.54 ℉). The most rainy month here is October, the average number of rainy days is 12.8. The least rainy month here is February, the average number of rainy days is 6.2. 
When travelling to some places in Dominican Republic, always consider the altitude of the the place as well. The highest point here is Pico Duarte (3098 m) and the lowest point is Lago Enriquillo (-46 m). So there are huge differences in altitudes in this country and the weather is very different in them therefore. 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 Dominican Republic in January is this: The average highest temperature in Dominican Republic in January is 28.7 ℃ (83.66 ℉). The average lowest temperature is 20.3 ℃ (68.54 ℉). At the beginning of January you can expect higher temperatures, the average highest temperature is around 29.2 ℃ (84.56 ℉). At the end of January you can expect higher temperatures, the average highest temperature is around 29 ℃ (84.2 ℉). The average number of rainy days in January is 7.7. The average rainfall is 62.9 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.These numbers above are valid primarily for the capital and the area around it. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Dominican Republic in February is this: The average highest temperature in Dominican Republic in February is 29.3 ℃ (84.74 ℉). The average lowest temperature is 19.6 ℃ (67.28 ℉). At the beginning of February you can expect lower temperatures, the average highest temperature is around 29 ℃ (84.2 ℉). At the end of February you can expect lower temperatures, the average highest temperature is around 29.2 ℃ (84.56 ℉). The average number of rainy days in February is 6.2. The average rainfall is 57.1 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 11:18 (hours and minutes), in the middle of the month 11:31 and at the end of the month 11:46.These numbers above are valid primarily for the capital and the area around it. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Dominican Republic in March is this: The average highest temperature in Dominican Republic in March is 29.1 ℃ (84.38 ℉). The average lowest temperature is 20 ℃ (68 ℉). At the beginning of March you can expect higher temperatures, the average highest temperature is around 29.2 ℃ (84.56 ℉). At the end of March you can expect higher temperatures, the average highest temperature is around 29.7 ℃ (85.46 ℉). The average number of rainy days in March is 6.3. The average rainfall is 52.9 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.These numbers above are valid primarily for the capital and the area around it. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Dominican Republic in April is this: The average highest temperature in Dominican Republic in April is 30.3 ℃ (86.54 ℉). The average lowest temperature is 21.4 ℃ (70.52 ℉). At the beginning of April you can expect lower temperatures, the average highest temperature is around 29.7 ℃ (85.46 ℉). At the end of April you can expect lower temperatures, the average highest temperature is around 30.1 ℃ (86.18 ℉). The average number of rainy days in April is 6.9. The average rainfall is 73.5 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 12:18 (hours and minutes), in the middle of the month 12:33 and at the end of the month 12:47.These numbers above are valid primarily for the capital and the area around it. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Dominican Republic in May is this: The average highest temperature in Dominican Republic in May is 29.9 ℃ (85.82 ℉). The average lowest temperature is 22.7 ℃ (72.86 ℉). At the beginning of May you can expect higher temperatures, the average highest temperature is around 30.1 ℃ (86.18 ℉). At the end of May you can expect higher temperatures, the average highest temperature is around 30.25 ℃ (86.45 ℉). The average number of rainy days in May is 11.5. The average rainfall is 191.1 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 12:47 (hours and minutes), in the middle of the month 13:00 and at the end of the month 13:09.These numbers above are valid primarily for the capital and the area around it. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Dominican Republic in June is this: The average highest temperature in Dominican Republic in June is 30.6 ℃ (87.08 ℉). The average lowest temperature is 23.3 ℃ (73.94 ℉). At the beginning of June you can expect lower temperatures, the average highest temperature is around 30.25 ℃ (86.45 ℉). At the end of June you can expect higher temperatures, the average highest temperature is around 31 ℃ (87.8 ℉). The average number of rainy days in June is 10.1. The average rainfall is 136.9 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 13:09 (hours and minutes), in the middle of the month 13:13 and at the end of the month 13:13.These numbers above are valid primarily for the capital and the area around it. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Dominican Republic in July is this: The average highest temperature in Dominican Republic in July is 31.4 ℃ (88.52 ℉). The average lowest temperature is 23.4 ℃ (74.12 ℉). At the beginning of July you can expect lower temperatures, the average highest temperature is around 31 ℃ (87.8 ℉). At the end of July you can expect higher temperatures, the average highest temperature is around 31.75 ℃ (89.15 ℉). The average number of rainy days in July is 11.5. The average rainfall is 146.2 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 13:13 (hours and minutes), in the middle of the month 13:08 and at the end of the month 12:59.These numbers above are valid primarily for the capital and the area around it. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Dominican Republic in August is this: The average highest temperature in Dominican Republic in August is 32.1 ℃ (89.78 ℉). The average lowest temperature is 23.2 ℃ (73.76 ℉). At the beginning of August you can expect lower temperatures, the average highest temperature is around 31.75 ℃ (89.15 ℉). At the end of August you can expect lower temperatures, the average highest temperature is around 31.8 ℃ (89.24 ℉). The average number of rainy days in August is 12.3. The average rainfall is 180.1 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.These numbers above are valid primarily for the capital and the area around it. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Dominican Republic in September is this: The average highest temperature in Dominican Republic in September is 31.5 ℃ (88.7 ℉). The average lowest temperature is 23.1 ℃ (73.58 ℉). At the beginning of September you can expect higher temperatures, the average highest temperature is around 31.8 ℃ (89.24 ℉). At the end of September you can expect lower temperatures, the average highest temperature is around 31.3 ℃ (88.34 ℉). The average number of rainy days in September is 11.6. The average rainfall is 177.2 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 12:33 (hours and minutes), in the middle of the month 12:18 and at the end of the month 12:02.These numbers above are valid primarily for the capital and the area around it. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Dominican Republic in October is this: The average highest temperature in Dominican Republic in October is 31.1 ℃ (87.98 ℉). The average lowest temperature is 23.1 ℃ (73.58 ℉). At the beginning of October you can expect higher temperatures, the average highest temperature is around 31.3 ℃ (88.34 ℉). At the end of October you can expect lower temperatures, the average highest temperature is around 31.05 ℃ (87.89 ℉). The average number of rainy days in October is 12.8. The average rainfall is 191.2 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 12:02 (hours and minutes), in the middle of the month 11:47 and at the end of the month 11:32.These numbers above are valid primarily for the capital and the area around it. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Dominican Republic in November is this: The average highest temperature in Dominican Republic in November is 31 ℃ (87.8 ℉). The average lowest temperature is 21.4 ℃ (70.52 ℉). At the beginning of November you can expect higher temperatures, the average highest temperature is around 31.05 ℃ (87.89 ℉). At the end of November you can expect lower temperatures, the average highest temperature is around 30.35 ℃ (86.63 ℉). The average number of rainy days in November is 9.2. The average rainfall is 98.8 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.These numbers above are valid primarily for the capital and the area around it. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.Typical (usual) weather in Dominican Republic in December is this: The average highest temperature in Dominican Republic in December is 29.7 ℃ (85.46 ℉). The average lowest temperature is 20 ℃ (68 ℉). At the beginning of December you can expect higher temperatures, the average highest temperature is around 30.35 ℃ (86.63 ℉). At the end of December you can expect lower temperatures, the average highest temperature is around 29.2 ℃ (84.56 ℉). The average number of rainy days in December is 8.9. The average rainfall is 85.9 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.These numbers above are valid primarily for the capital and the area around it. It is important to say, that the weather may differ significantly in different altitudes, especially in mountains.| Santo Domingo | temperature: - | highest temperature: 29.7 ℃ (85.46 ℉) | lowest temperature: 20 ℃ (68 ℉) | rainfall: 85.9mm | rainy days: 8.9 |
| Barahona | temperature: - | highest temperature: 29.3 ℃ (84.74 ℉) | lowest temperature: 21.4 ℃ (70.52 ℉) | rainfall: 43.4mm | rainy days: 2.4 |
| La Romana | temperature: - | highest temperature: 29.5 ℃ (85.1 ℉) | lowest temperature: 20 ℃ (68 ℉) | rainfall: 48.3mm | rainy days: 6.1 |
| Montecristi | temperature: - | highest temperature: 28.8 ℃ (83.84 ℉) | lowest temperature: 19.9 ℃ (67.82 ℉) | rainfall: 85.4mm | rainy days: 6.7 |
| Puerto Plata | temperature: - | highest temperature: 29 ℃ (84.2 ℉) | lowest temperature: 18.6 ℃ (65.48 ℉) | rainfall: 226.1mm | rainy days: 15.1 |
| Punta Cana | temperature: - | highest temperature: 29 ℃ (84.2 ℉) | lowest temperature: 23 ℃ (73.4 ℉) | rainfall: 79.8mm | rainy days: 10.7 |
| San Juan | temperature: - | highest temperature: 29.4 ℃ (84.92 ℉) | lowest temperature: 16 ℃ (60.8 ℉) | rainfall: 17.9mm | rainy days: 1.7 |
| Santiago | temperature: - | highest temperature: 28.2 ℃ (82.76 ℉) | lowest temperature: 19 ℃ (66.2 ℉) | rainfall: 79.7mm | rainy days: 10.1 |