Do you need to know, when is the best time to go to Sulawesi? Then you should take a look here, what weather you can expect there during the year.
Sulawesi is part of Indonesia. The climate of Indonesia is tropical. You can expect hot and humid weather, but more moderate weather in highlands. Temperatures remain fairly constant throughout the year, they are higher at the coast and a little bit lower in the inland.
When speaking about the usual weather in this area, the information is relevant for example for these popular places: Ampana, Bangka, Bitung, Bogani Nani Wartabone National Park, Bunaken, Central Sulawesi, Gorontalo, Kendari, Lore Lindu National Park, Luwuk, Makassar, Mamuju, Manado, Northern Sulawesi, Palopo, Palu, Rantepao, Southeast Sulawesi, Southern Sulawesi, Tana Toraja, Tangkoko Nature Reserve, Tanjung Bira, Tentena, Togian Islands, Tomohon, Wakatobi.
Let's look now what weather you can expect in the area around Manado and in many other cities. The warmest month here is August, the average maximum temperature is 32.8 ℃ (91.04 ℉). The average minimum temperature in this month is 20.9 ℃ (69.62 ℉). The coldest month here is December, the average maximum temperature is 30.9 ℃ (87.62 ℉). The average minimum temperature in this month is 22.9 ℃ (73.22 ℉). The most rainy month here is January, the average number of rainy days is 25.8. The least rainy month here is July, the average number of rainy days is 9.9. 
When travelling around Sulawesi, always consider the altitude of the the place as well. We should remind you, that the highest point in Indonesia is Puncak Jaya (4884 m) and the lowest point is Indian Ocean (0 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 Sulawesi in January is this: The average highest temperature in Sulawesi in January is 31 ℃ (87.8 ℉). The average lowest temperature is 22.2 ℃ (71.96 ℉). At the beginning of January you can expect lower temperatures, the average highest temperature is around 30.95 ℃ (87.71 ℉). At the end of January you can expect higher temperatures, the average highest temperature is around 31.05 ℃ (87.89 ℉). The average number of rainy days in January is 25.8. The average rainfall is 424.9 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 12:02 (hours and minutes), in the middle of the month 12:02 and at the end of the month 12:03.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 Sulawesi in February is this: The average highest temperature in Sulawesi in February is 31.1 ℃ (87.98 ℉). The average lowest temperature is 22.5 ℃ (72.5 ℉). At the beginning of February you can expect lower temperatures, the average highest temperature is around 31.05 ℃ (87.89 ℉). At the end of February you can expect lower temperatures, the average highest temperature is around 31.05 ℃ (87.89 ℉). The average number of rainy days in February is 22.3. The average rainfall is 376.5 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 12:03 (hours and minutes), in the middle of the month 12:04 and at the end of the month 12:05.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 Sulawesi in March is this: The average highest temperature in Sulawesi in March is 31 ℃ (87.8 ℉). The average lowest temperature is 21.5 ℃ (70.7 ℉). At the beginning of March you can expect higher temperatures, the average highest temperature is around 31.05 ℃ (87.89 ℉). At the end of March you can expect higher temperatures, the average highest temperature is around 31.4 ℃ (88.52 ℉). The average number of rainy days in March is 22.6. The average rainfall is 334.8 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 12:05 (hours and minutes), in the middle of the month 12:06 and at the end of the month 12:07.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 Sulawesi in April is this: The average highest temperature in Sulawesi in April is 31.8 ℃ (89.24 ℉). The average lowest temperature is 22.3 ℃ (72.14 ℉). At the beginning of April you can expect lower temperatures, the average highest temperature is around 31.4 ℃ (88.52 ℉). At the end of April you can expect higher temperatures, the average highest temperature is around 31.85 ℃ (89.33 ℉). The average number of rainy days in April is 18. The average rainfall is 289.1 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 12:07 (hours and minutes), in the middle of the month 12:08 and at the end of the month 12:10.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 Sulawesi in May is this: The average highest temperature in Sulawesi in May is 31.9 ℃ (89.42 ℉). The average lowest temperature is 22.5 ℃ (72.5 ℉). At the beginning of May you can expect lower temperatures, the average highest temperature is around 31.85 ℃ (89.33 ℉). At the end of May you can expect lower temperatures, the average highest temperature is around 31.7 ℃ (89.06 ℉). The average number of rainy days in May is 22.3. The average rainfall is 255.2 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 12:10 (hours and minutes), in the middle of the month 12:11 and at the end of the month 12:11.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 Sulawesi in June is this: The average highest temperature in Sulawesi in June is 31.5 ℃ (88.7 ℉). The average lowest temperature is 23 ℃ (73.4 ℉). At the beginning of June you can expect higher temperatures, the average highest temperature is around 31.7 ℃ (89.06 ℉). At the end of June you can expect lower temperatures, the average highest temperature is around 31.3 ℃ (88.34 ℉). The average number of rainy days in June is 19.4. The average rainfall is 236.8 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 12:11 (hours and minutes), in the middle of the month 12:12 and at the end of the month 12:12.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 Sulawesi in July is this: The average highest temperature in Sulawesi in July is 31.1 ℃ (87.98 ℉). The average lowest temperature is 21.4 ℃ (70.52 ℉). At the beginning of July you can expect higher temperatures, the average highest temperature is around 31.3 ℃ (88.34 ℉). At the end of July you can expect higher temperatures, the average highest temperature is around 31.95 ℃ (89.51 ℉). The average number of rainy days in July is 9.9. The average rainfall is 128.4 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 12:12 (hours and minutes), in the middle of the month 12:11 and at the end of the month 12:11.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 Sulawesi in August is this: The average highest temperature in Sulawesi in August is 32.8 ℃ (91.04 ℉). The average lowest temperature is 20.9 ℃ (69.62 ℉). At the beginning of August you can expect lower temperatures, the average highest temperature is around 31.95 ℃ (89.51 ℉). At the end of August you can expect lower temperatures, the average highest temperature is around 32.35 ℃ (90.23 ℉). The average number of rainy days in August is 10.8. The average rainfall is 135.6 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 12:11 (hours and minutes), in the middle of the month 12:09 and at the end of the month 12:08.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 Sulawesi in September is this: The average highest temperature in Sulawesi in September is 31.9 ℃ (89.42 ℉). The average lowest temperature is 21.3 ℃ (70.34 ℉). At the beginning of September you can expect higher temperatures, the average highest temperature is around 32.35 ℃ (90.23 ℉). At the end of September you can expect higher temperatures, the average highest temperature is around 32.05 ℃ (89.69 ℉). The average number of rainy days in September is 19.2. The average rainfall is 174.7 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 12:08 (hours and minutes), in the middle of the month 12:07 and at the end of the month 12:06.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 Sulawesi in October is this: The average highest temperature in Sulawesi in October is 32.2 ℃ (89.96 ℉). The average lowest temperature is 22.1 ℃ (71.78 ℉). At the beginning of October you can expect lower temperatures, the average highest temperature is around 32.05 ℃ (89.69 ℉). At the end of October you can expect lower temperatures, the average highest temperature is around 31.85 ℃ (89.33 ℉). The average number of rainy days in October is 14.9. The average rainfall is 196.6 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 12:06 (hours and minutes), in the middle of the month 12:05 and at the end of the month 12:04.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 Sulawesi in November is this: The average highest temperature in Sulawesi in November is 31.5 ℃ (88.7 ℉). The average lowest temperature is 23.3 ℃ (73.94 ℉). At the beginning of November you can expect higher temperatures, the average highest temperature is around 31.85 ℃ (89.33 ℉). At the end of November you can expect lower temperatures, the average highest temperature is around 31.2 ℃ (88.16 ℉). The average number of rainy days in November is 20. The average rainfall is 282 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 12:04 (hours and minutes), in the middle of the month 12:03 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 Sulawesi in December is this: The average highest temperature in Sulawesi in December is 30.9 ℃ (87.62 ℉). The average lowest temperature is 22.9 ℃ (73.22 ℉). At the beginning of December you can expect higher temperatures, the average highest temperature is around 31.2 ℃ (88.16 ℉). At the end of December you can expect higher temperatures, the average highest temperature is around 30.95 ℃ (87.71 ℉). The average number of rainy days in December is 22.9. The average rainfall is 363.3 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 12:02 (hours and minutes), in the middle of the month 12:02 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.