September weather forecast
Surabaya, Indonesia

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The skyscrapers making the cityscape of Surabaya in East Java, Indonesia
The skyscrapers making the cityscape of Surabaya in East Java, Indonesia

Weather in September

Surabaya's weather in September heralds the dry season's final phase with significantly less rainfall compared to the early months of the year. Mild temperatures remain the norm, making both days and nights pleasantly warm. Sea temperatures start to rise gradually, signaling the wet season's gradual onset. As September concludes, the declining sunshine hours symbolize the impending end of the dry season. With less stingy sun rays kissing the city, outdoor activities continue to flourish without the menace of harsh heatwaves.

Temperature

The shift from August to September is characterized by an average high-temperature of a still tropical 31.7°C (89.1°F), not significantly different from the 30.8°C (87.4°F) of August. During September, the average low-temperature is a warm 24.4°C (75.9°F).

Heat index

September's mean heat index is evaluated at a fiery hot 38°C (100.4°F). Adopt additional preventive measures, heat cramps and heat exhaustion are potential outcomes. Prolonged activity may trigger heatstroke.
When considering the heat index, it's pivotal to note it is for shade and mild wind conditions. Exposure to the sun directly might heighten the heat index by 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'feels like' or 'apparent temperature', is found by incorporating humidity levels into the air temperature measurement. The influence of weather can be personal, changing with an individual's body mass, height, and level of physical exertion. Being aware that direct sunlight can impact the felt heat might mean an increase in the heat index by 15 Fahrenheit (8 Celsius) degrees. Heat index values are extremely significant for babies and toddlers. Younglings frequently fail to recognize the requirement to rest and rehydrate. Thirst emerges late in dehydration - it is imperative to keep hydration levels high, particularly during extended physical exertions.
In response to overheating, the human body perspires to cool down, mainly through the evaporation of sweat. An increase in relative humidity retards evaporation, subsequently reducing the body's heat removal rate and leading to a sensation of being overly warm. Elevated heat gain compared to the body's release capability poses risks of dehydration and potential overheating.

Humidity

In Surabaya, Indonesia, the average relative humidity in September is 65%.

Rainfall

In September, in Surabaya, the rain falls for 4.1 days. Throughout September, 8mm (0.31") of precipitation is accumulated. In Surabaya, during the entire year, the rain falls for 187.8 days and collects up to 839mm (33.03") of precipitation.

Sea temperature

In Surabaya, the average seawater temperature in September is 28.1°C (82.6°F).
Note: Water temperatures ranging between 25°C (77°F) and 29°C (84.2°F) are regarded as very warm, making swimming, diving, and similar water activities pleasurable for extended periods.

Daylight

In September, the average length of the day is 12h and 4min.
On the first day of the month, sunrise is at 05:29 and sunset at 17:28. On the last day of September, sunrise is at 05:13 and sunset at 17:23 WIB.

Sunshine

The months with the most sunshine are August through October, with an average of 9.9h of sunshine.

UV index

January through December, with an average maximum UV index of 7, are months with the highest UV index in Surabaya. The months with the lowest UV index in Surabaya are January through December, with an average maximum UV index of 7. A UV Index of 6 to 7 symbolizes a high threat to health from unsafe exposure to UV radiation for ordinary individuals.
Note: In September, the UV index of 7 transforms into the following advice:
Use protective steps and abide by sun safety guidelines. Safeguarding against skin and eye harm is necessary. From 10 a.m. to 4 p.m., when UV radiation is at its strongest, limit direct exposure to the Sun and note that shade structures may not provide full sun protection. For excellent sun protection for the eyes, ears, face, and neck, consider a wide-brim hat. Notice! The Sun's UV exposure elevates with sand and water reflections.

Frequently asked questions

How hot does it get in Surabaya in September?

The high-temperature, in September, in Surabaya, is 31.7°C (89.1°F), while the low-temperature averages to 24.4°C (75.9°F). The average heat index (a.k.a. 'feels like', 'apparent temperature'), which takes the relative humidity and factors it into the air temperature reading, in September is evaluated at 38°C (100.4°F).

What is the average humidity in September in Surabaya?

In September, the average relative humidity in Surabaya, Indonesia, is 65%.

How much does it rain in Surabaya in September?

In Surabaya, during September, the rain falls for 4.1 days and regularly aggregates up to 8mm (0.31") of precipitation.

How warm is the water in September in Surabaya?

In Surabaya, Indonesia, in September, the average water temperature is 28.1°C (82.6°F). For any water activity, surface water temperatures between 25°C (77°F) and 29°C (84.2°F) are considered as excellent and extremely pleasant for lengthened periods.

How many hours of daylight does Surabaya have in September?

The average day length in September in Surabaya, Indonesia, is 12h and 4min.

When is the sunrise / sunset in September in Surabaya?

On the first day of September in Surabaya, Indonesia, sunrise is at 05:29 and sunset at 17:28. On the last day of the month, sunrise is at 05:13 and sunset at 17:23 WIB.

What are the months with the most sunshine in Surabaya?

The months with the most sunshine in Surabaya, Indonesia, are August through October, with an average of 9.9h of sunshine.

How many hours of sunshine does Surabaya have in September?

In September, the average sunshine duration is 9.9h.

What are the months with the highest UV index in Surabaya?

The months with the highest UV index are January through December, with an average maximum UV index of 7.

When is the lowest UV index in Surabaya?

The months with the lowest UV index in Surabaya are January through December, with an average maximum UV index of 7.

What is the UV index reading in September in Surabaya?

In Surabaya, the average daily maximum UV index in September is 7. A UV Index estimate of 6 to 7 represents a high health threat from exposure to Sun's UV rays.

Average temperature in September
Surabaya, Indonesia

Average temperature in September - Surabaya, Indonesia
  • Average high temperature in September: 31.7°C

The warmest month (with the highest average high temperature) is October (32.9°C).
The months with the lowest average high temperature are January, February and July (30.1°C).

  • Average low temperature in September: 24.4°C

The month with the highest average low temperature is November (26.5°C).
The coldest month (with the lowest average low temperature) is August (24.2°C).

Average pressure in September
Surabaya, Indonesia

Average pressure in September - Surabaya, Indonesia
  • Average pressure in September: 1011.3mbar

The month with the highest atmospheric pressure is August (1011.4mbar).
The month with the lowest atmospheric pressure is December (1008.7mbar).

Average wind speed in September
Surabaya, Indonesia

Average wind speed in September - Surabaya, Indonesia
  • Average wind speed in September: 9.7km/h

The windiest month (with the highest average wind speed) is August (9.9km/h).
The calmest month (with the lowest average wind speed) is April (6.3km/h).

Average humidity in September
Surabaya, Indonesia

Average humidity in September - Surabaya, Indonesia
  • Average humidity in September: 65%

The month with the highest relative humidity is February (79%).
The month with the lowest relative humidity is October (63%).

Average rainfall in September
Surabaya, Indonesia

Average rainfall in September - Surabaya, Indonesia
  • Average rainfall in September: 8mm

The wettest month (with the highest rainfall) is February (179mm).
The driest month (with the least rainfall) is August (4mm).

Average rainfall days in September
Surabaya, Indonesia

Average rainfall days in September - Surabaya, Indonesia
  • Average rainfall days in September: 4.1 days

The month with the highest number of rainy days is January (27 days).
The month with the least rainy days is August (3.7 days).

Average sea temperature in September
Surabaya, Indonesia

Average sea temperature in September - Surabaya, Indonesia
  • Average sea temperature in September: 28.1°C

The best month for swimming (with the highest average sea temperature) is December (30.2°C).
The coldest month (with the lowest average sea temperature) is August (27.8°C).

Average daylight in September /
Average sunshine in September
Surabaya, Indonesia

Average daylight in September / Average sunshine in September - Surabaya, Indonesia
  • Average daylight in September: 12h and 1min

The month with the longest days is December (Average daylight: 12h and 30min).
The month with the shortest days is June (Average daylight: 11h and 42min).

  • Average sunshine in September: 9h and 5min

The months with the most sunshine are August, September and October (Average sunshine: 9h and 54min).
The month with the least sunshine is January (Average sunshine: 8h and 6min).

Average sunshine days in September
Surabaya, Indonesia

Average sunshine days in September - Surabaya, Indonesia
  • Average sunshine days in September: 23.7 days

The month with the most sunshine days is August (26 days).
The month with the least sunshine days is February (2.8 days).

Average UV index in September
Surabaya, Indonesia

Average UV index in September - Surabaya, Indonesia
  • Average UV index in September: 7

The months with the highest UV index are January, February, March, April, May, June, July, August, September, October, November and December (UV index 7).
The months with the lowest UV index are January, February, March, April, May, June, July, August, September, October, November and December (UV index 7).

Average cloud cover in September
Surabaya, Indonesia

Average cloud cover in September - Surabaya, Indonesia
  • Average cloud cover in September: 12

The month with the most cloud cover is January (Cloud cover 44).
The month with the least cloud cover is August (Cloud cover 11).

Average visibility in September
Surabaya, Indonesia

Average visibility in September - Surabaya, Indonesia
  • Average visibility in September: 10km

The months with the highest visibility are March, April, May, June, July, August, September, October, November and December (10km).
The months with the lowest visibility are January and February (9km).

Surabaya, Indonesia

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