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

September observes an average high-temperature of a still tropical 31.7°C, marking an insignificant difference from August's 30.8°C. An average low-temperature of 24.4°C is recorded in the month of September in Surabaya.

Heat index

In September, the average heat index is estimated at a very hot 38°C. Ensure extra safety measures, heat exhaustion and heat cramps are likely. Continuous activity might result in heatstroke.
Note that heat index values are valued for light wind and location in the shade. An exposure to direct sunlight may lift the heat index values by 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'apparent temperature' or 'feels like', is a value derived by merging air temperature with the humidity to convey how the climate feels. This effect is subjective, differing among individuals based on their physical activity and perception of heat, which can be influenced by factors like wind, clothing, and metabolic variances. Under direct sun rays, the felt temperature might be heightened, with the heat index increasing by 15 Fahrenheit (8 Celsius) degrees. Heat index values are extremely vital to babies and toddlers. Youths are typically more endangered than adults since they usually sweat less. Their larger skin surface concerning their smaller bodies and higher heat production due to activity further adds to their vulnerability.
As a reaction to high temperatures, the human body begins to perspire, using the evaporation of sweat to lower its temperature. Relative humidity in excess curtails evaporation, therefore reducing heat dissipation from the body, leading to feelings of excess heat. Overheating dangers loom when the body's heat release mechanisms are overshadowed by excessive gain.

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 of precipitation is accumulated. Throughout the year, there are 187.8 rainfall days, and 839mm of precipitation is accumulated.

Sea temperature

In Surabaya, in September, the average water temperature is 28.1°C.
Note: Surface water temperatures ranging from 25°C to 29°C are considered superb and highly pleasant for water activities over extended periods.

Daylight

In Surabaya, the average length of the day in September is 12h and 4min.
On the first day of the month, sunrise is at 05:30 and sunset at 17:28. On the last day of September, sunrise is at 05:14 and sunset at 17:23 WIB.

Sunshine

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

UV index

January through December, with an average maximum UV index of 7, are months with the highest UV index in Surabaya. January through December, with an average maximum UV index of 7, are months with the lowest UV index. A UV Index reading of 6 to 7 represents a high health hazard from unprotected exposure to Sun's UV rays for ordinary individuals.
Note: In September, the average maximum UV index of 7 translates into the following recommendations:
Act on precautions and pay attention to sun safety recommendations. Avoidance of sunburn is obligatory. Between 10 a.m. and 4 p.m., UV radiation is strongest. Make an effort to avoid direct sunlight during this time, remembering that shade structures may not provide full sun protection. Wearing a wide-brim hat can block approximately 50% of UV radiation, protecting the eyes. Be attentive! The UV exposure is heightened with reflections from sand and water.