Honolulu
Hawaii, USA
Long-term weather forecast
Long-term weather forecast

September weather forecast and climate
Honolulu, HI

Waikiki beach viewed from above, with clear calm waters on the foot of Honolulu city, Hawaii, with the vast cityscape and mountains in the distance
Waikiki beach viewed from above, with clear calm waters on the foot of Honolulu city, Hawaii, with the vast cityscape and mountains in the distance
September, the first month of the autumn, in Honolulu, is still a warm month, with average temperature fluctuating between 75.6°F (24.2°C) and 81.5°F (27.5°C).

Temperature

With an average high-temperature of 81.5°F (27.5°C) and an average low-temperature of 75.6°F (24.2°C), September is the warmest month.

Heat index

In September, the average heat index is calculated to a tropical 86.4°F (30.2°C). Exhaustion is likely with prolonged exposure and activity. Sustaining activity may result in heat cramps.
Take into consideration that the heat index values are calculated for shade and light wind conditions. Exposure to direct sunshine can increase heat index values by up to 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'felt air temperature', 'real feel', 'feels like', or 'apparent temperature', combines air temperature and relative humidity to represent a human perceived temperature equivalent. Additional factors like activity, metabolic differences, wind, and differences in body mass, height, and shape affect individual temperature impact. Bear in mind that direct sunshine exposure increases weather impact, and may raise heat index by up to 15 Fahrenheit (8 Celsius) degrees. Heat index values are especially crucial for babies and toddlers. Young children are generally more endangered than adults, as they usually less sweat. And also, due to larger skin surface relative to their small bodies and higher heat production as a result of their activity.

Humidity

Months with the lowest humidity are April, May, September and November, with an average relative humidity of 74%.

Rainfall

In Honolulu, during September, the rain falls for 17.9 days and regularly aggregates up to 1.22" (31mm) of precipitation. Throughout the year, there are 197.2 rainfall days, and 14.61" (371mm) of precipitation is accumulated.

Ocean temperature

The month with the warmest seawater in Honolulu is September, with an average ocean temperature of 80.4°F (26.9°C).
Note: Water temperature between 77°F (25°C) and 84.2°F (29°C) is regarded as very warm and enjoyable by all. With these temperatures, water activities are pleasurable, without feeling uncomfortable for prolonged periods.

Daylight

The average length of the day in September is 12.3h.

Sunshine

In September, the average sunshine is 8.9h.

UV index

Months with the highest UV index in Honolulu are July through September, with an average maximum UV index of 7. A UV Index of 6 to 7 symbolizes a high health vulnerability from the exposure to the Sun's UV radiation for average individuals.
Note: The average daily UV index of 7 transform into the following instructions:
Take precautions and adopt sun safety practices. Protection against sunburn is obliged. The Sun's UV radiation is most powerful between 10 a.m. and 4 p.m. To the extent possible, limit exposure to the direct sun during these hours. Sun-protective clothing, a long-sleeved shirt and pants, a wide-brimmed hat, and UVA and UVB-blocking sunglasses are particularly helpful in blocking UV radiation's harmful effects. Caution! The reflection of sand and water significantly increases the intensity of the Sun's UV radiation.

What is the warmest month in Honolulu?

With an average high-temperature of 81.5°F (27.5°C) and an average low-temperature of 75.6°F (24.2°C), September is the warmest month in Honolulu.

What is the temperature in September in Honolulu?

The average high-temperature, in September, in Honolulu, Hawaii, is 81.5°F (27.5°C), while the average low-temperature is 75.6°F (24.2°C). The average heat index (a.k.a. 'feels like', 'apparent temperature'), that combines both air temperature and relative humidity, in September is appraised at 86.4°F (30.2°C).

What are the least humid months in Honolulu?

Months with the lowest humidity in Honolulu, Hawaii, are April, May, September and November, with an average relative humidity of 74%.

What is the average humidity in September in Honolulu?

In September, the average relative humidity in Honolulu is 74%.

How much does it rain in Honolulu in September?

In Honolulu, Hawaii, during September, the rain falls for 17.9 days and regularly aggregates up to 1.22" (31mm) of precipitation.

What is the month with the warmest ocean in Honolulu?

The month with the warmest seawater in Honolulu is September, with an average ocean temperature of 80.4°F (26.9°C).

What is the ocean temperature in September in Honolulu?

In September, the average ocean temperature in Honolulu is 80.4°F (26.9°C). For swimming, diving, and other water activities, temperatures between 77°F (25°C) and 84.2°F (29°C) are perceived as very enjoyable and pleasurable for prolonged periods without feeling uncomfortable.

How many hours of daylight does Honolulu have in September?

The average length of the day in September in Honolulu, Hawaii, is 12.3h.

How long on average sun shines in September in Honolulu?

The average sunshine in September is 8.9h.

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

July through September, with an average maximum UV index of 7, are months with the highest UV index.

How high is the UV index in September in Honolulu?

The average daily maximum UV index in September in Honolulu, Hawaii, is 7. A UV Index of 6 to 7 symbolizes a high health threat from the exposure to the Sun's UV rays.
Average temperature in September - Honolulu, HI
  • Average high temperature in September: 27.5°C

The warmest month (with the highest average high temperature) is September (27.5°C).
Months with the lowest average high temperature are February and March (23.9°C).

  • Average low temperature in September: 24.2°C

The month with the highest average low temperature is August (24.3°C).
The coldest month (with the lowest average low temperature) is February (20.6°C).

Average humidity in September - Honolulu, HI
  • Average humidity in September: 74%

Months with the highest relative humidity are February and December (76%).
Months with the lowest relative humidity are April, May, September and November (74%).

Average rainfall in September - Honolulu, HI
  • Average rainfall in September: 31mm

Wettest months (with the highest rainfall) are March and October (46mm).
The driest month (with the lowest rainfall) is July (17mm).

Average rainfall days in September - Honolulu, HI
  • Average rainfall days in September: 17.9 days

Months with the highest number of rainy days are March and October (18 days).
The month with the lowest number of rainy days is January (12.6 days).

Average sea temperature in September - Honolulu, HI
  • Average sea temperature in September: 26.9°C

The best month for swimming (with the highest average sea temperature) is September (26.9°C).
The coldest month (with the lowest average sea temperature) is March (24.3°C).

Average daylight in September / Average sunshine in September - Honolulu, HI
  • Average daylight in September: 12.3h

The month with the longest days is June (Average daylight: 13.4h).
The month with shortest days is December (Average daylight: 10.9h).

  • Average sunshine in September: 8.9h

The month with most sunshine is June (Average sunshine: 10.8h).
Months with least sunshine are November and December (Average sunshine: 6.5).

Average UV index in September - Honolulu, HI
  • Average UV index in September: 7

Months with the highest UV index are July, August and September (UV index 7).
Months with the lowest UV index are January, February, March, April, May, June, October, November and December (UV index 6).