September weather forecast
Surabaya, Indonesia

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.