Do you need to know, when is the best time to go to Brunei? Then you should take a look here, what weather you can expect there during the year.
The climate of Brunei is tropical, hot and humid. At higher altitudes you can expect heavy rainfall sometimes. Dry season is very hot, rainy season is usually warm and wet.
When speaking about the usual weather in this state, the information is relevant for example for these popular places: Bandar Seri Begawan, Bangar, Kuala Belait.
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 May, the average maximum temperature is 33.4 ℃ (92.12 ℉). The average minimum temperature in this month is 23.6 ℃ (74.48 ℉). The coldest month here is January, the average maximum temperature is 30.8 ℃ (87.44 ℉). The average minimum temperature in this month is 23.7 ℃ (74.66 ℉). The most rainy month here is November, the average number of rainy days is 22.7. The least rainy month here is March, the average number of rainy days is 11.1. 
When travelling to some places in Brunei, always consider the altitude of the the place as well. The highest point here is Bukit Pagon (1850 m) and the lowest point is South China 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 Brunei in January is this: The average highest temperature in Brunei in January is 30.8 ℃ (87.44 ℉). The average lowest temperature is 23.7 ℃ (74.66 ℉). At the beginning of January you can expect higher temperatures, the average highest temperature is around 31.35 ℃ (88.43 ℉). At the end of January you can expect higher temperatures, the average highest temperature is around 31.25 ℃ (88.25 ℉). The average number of rainy days in January is 15.9. The average rainfall is 294.2 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 11:50 (hours and minutes), in the middle of the month 11:51 and at the end of the month 11:54.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 Brunei in February is this: The average highest temperature in Brunei in February is 31.7 ℃ (89.06 ℉). The average lowest temperature is 23.2 ℃ (73.76 ℉). At the beginning of February you can expect lower temperatures, the average highest temperature is around 31.25 ℃ (88.25 ℉). At the end of February you can expect higher temperatures, the average highest temperature is around 31.95 ℃ (89.51 ℉). The average number of rainy days in February is 12. The average rainfall is 157.7 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 11:54 (hours and minutes), in the middle of the month 11:57 and at the end of the month 12:01.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.Typical (usual) weather in Brunei in March is this: The average highest temperature in Brunei in March is 32.2 ℃ (89.96 ℉). The average lowest temperature is 23.6 ℃ (74.48 ℉). At the beginning of March you can expect lower temperatures, the average highest temperature is around 31.95 ℃ (89.51 ℉). At the end of March you can expect higher temperatures, the average highest temperature is around 32.75 ℃ (90.95 ℉). The average number of rainy days in March is 11.1. The average rainfall is 119.5 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 12:01 (hours and minutes), in the middle of the month 12:05 and at the end of the month 12:09.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 Brunei in April is this: The average highest temperature in Brunei in April is 33.3 ℃ (91.94 ℉). The average lowest temperature is 23.3 ℃ (73.94 ℉). At the beginning of April you can expect lower temperatures, the average highest temperature is around 32.75 ℃ (90.95 ℉). At the end of April you can expect higher temperatures, the average highest temperature is around 33.35 ℃ (92.03 ℉). The average number of rainy days in April is 16.4. The average rainfall is 190.9 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 12:09 (hours and minutes), in the middle of the month 12:13 and at the end of the month 12:17.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 Brunei in May is this: The average highest temperature in Brunei in May is 33.4 ℃ (92.12 ℉). The average lowest temperature is 23.6 ℃ (74.48 ℉). At the beginning of May you can expect lower temperatures, the average highest temperature is around 33.35 ℃ (92.03 ℉). At the end of May you can expect lower temperatures, the average highest temperature is around 33.05 ℃ (91.49 ℉). The average number of rainy days in May is 18.3. The average rainfall is 239.2 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 12:17 (hours and minutes), in the middle of the month 12:20 and at the end of the month 12:23.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 Brunei in June is this: The average highest temperature in Brunei in June is 32.7 ℃ (90.86 ℉). The average lowest temperature is 23.9 ℃ (75.02 ℉). At the beginning of June you can expect higher temperatures, the average highest temperature is around 33.05 ℃ (91.49 ℉). At the end of June you can expect higher temperatures, the average highest temperature is around 32.9 ℃ (91.22 ℉). The average number of rainy days in June is 16.4. The average rainfall is 209.7 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 12:23 (hours and minutes), in the middle of the month 12:24 and at the end of the month 12:24.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 Brunei in July is this: The average highest temperature in Brunei in July is 33.1 ℃ (91.58 ℉). The average lowest temperature is 22.8 ℃ (73.04 ℉). At the beginning of July you can expect lower temperatures, the average highest temperature is around 32.9 ℃ (91.22 ℉). At the end of July you can expect lower temperatures, the average highest temperature is around 32.65 ℃ (90.77 ℉). The average number of rainy days in July is 15.7. The average rainfall is 223.8 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 12:24 (hours and minutes), in the middle of the month 12:22 and at the end of the month 12:20.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 Brunei in August is this: The average highest temperature in Brunei in August is 32.2 ℃ (89.96 ℉). The average lowest temperature is 22.8 ℃ (73.04 ℉). At the beginning of August you can expect higher temperatures, the average highest temperature is around 32.65 ℃ (90.77 ℉). At the end of August you can expect higher temperatures, the average highest temperature is around 32.3 ℃ (90.14 ℉). The average number of rainy days in August is 16. The average rainfall is 221 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 12:20 (hours and minutes), in the middle of the month 12:17 and at the end of the month 12:13.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 Brunei in September is this: The average highest temperature in Brunei in September is 32.4 ℃ (90.32 ℉). The average lowest temperature is 22.8 ℃ (73.04 ℉). At the beginning of September you can expect lower temperatures, the average highest temperature is around 32.3 ℃ (90.14 ℉). At the end of September you can expect lower temperatures, the average highest temperature is around 32.35 ℃ (90.23 ℉). The average number of rainy days in September is 19.2. The average rainfall is 260.2 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 12:13 (hours and minutes), in the middle of the month 12:09 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 Brunei in October is this: The average highest temperature in Brunei in October is 32.3 ℃ (90.14 ℉). The average lowest temperature is 23.4 ℃ (74.12 ℉). At the beginning of October you can expect higher temperatures, the average highest temperature is around 32.35 ℃ (90.23 ℉). At the end of October you can expect lower temperatures, the average highest temperature is around 32.1 ℃ (89.78 ℉). The average number of rainy days in October is 21.3. The average rainfall is 311.7 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 12:05 (hours and minutes), in the middle of the month 12:01 and at the end of the month 11:57.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 Brunei in November is this: The average highest temperature in Brunei in November is 31.9 ℃ (89.42 ℉). The average lowest temperature is 23.1 ℃ (73.58 ℉). At the beginning of November you can expect higher temperatures, the average highest temperature is around 32.1 ℃ (89.78 ℉). At the end of November you can expect lower temperatures, the average highest temperature is around 31.9 ℃ (89.42 ℉). The average number of rainy days in November is 22.7. The average rainfall is 343.1 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 11:57 (hours and minutes), in the middle of the month 11:54 and at the end of the month 11:52.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 Brunei in December is this: The average highest temperature in Brunei in December is 31.9 ℃ (89.42 ℉). The average lowest temperature is 23 ℃ (73.4 ℉). At the beginning of December you can expect lower temperatures, the average highest temperature is around 31.9 ℃ (89.42 ℉). At the end of December you can expect lower temperatures, the average highest temperature is around 31.35 ℃ (88.43 ℉). The average number of rainy days in December is 20.8. The average rainfall is 339.8 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 11:52 (hours and minutes), in the middle of the month 11:50 and at the end of the month 11:50.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.