September weather forecast
Honolulu, HI

Waikiki beach with clear calm waters on the foot of Honolulu city, Hawaii, with the vast cityscape and mountains in the distance
Waikiki beach with clear calm waters on the foot of Honolulu city, Hawaii, with the vast cityscape and mountains in the distance

Weather in September

The first month of the autumn, September, is still a warm month in Honolulu, Hawaii, with an average temperature fluctuating between 75.6°F (24.2°C) and 81.5°F (27.5°C).

Temperature

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

Heat index

The average heat index in September is computed to be a tropical 86.4°F (30.2°C). Exhaustion is likely with prolonged exposure and activity. Sustaining activity may result in heat cramps.
Note that heat index values are valued for light wind and location in the shade. With exposure to direct sunlight, the heat index may be increased by up to 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'real feel', 'apparent temperature', 'feels like', or 'felt air temperature', is a measure that combines air temperature and relative humidity into a single value that indicates how hot the weather feels. This effect is individual, with diverse people perceiving weather differently for numerous reasons (wind, clothing, pregnancy), and activity. Be aware that direct exposure to sunlight increases heat impact and may raise the 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

April, May, September and November, with an average relative humidity of 74%, are the least humid months in Honolulu.

Rainfall

In Honolulu, it is raining for 17.9 days, with typically 1.22" (31mm) of accumulated precipitation. Throughout the year, there are 197.2 rainfall days, and 14.61" (371mm) of precipitation is accumulated.

Ocean temperature

With an average ocean temperature of 80.4°F (26.9°C), September is the month with the warmest seawater in Honolulu.
Note: For any water activity, surface water temperatures between 77°F (25°C) and 84.2°F (29°C) are considered as excellent and extremely pleasant for lengthened periods.

Daylight

In Honolulu, Hawaii, the average length of the day in September is 12h and 15min.
On the first day of the month, sunrise is at 6:15 am and sunset at 6:47 pm. On the last day of September, in Honolulu, sunrise is at 6:22 am and sunset at 6:20 pm HST.

Sunshine

The average sunshine in September in Honolulu is 8.9h.

UV index

July through September, with an average maximum UV index of 7, are months with the highest UV index. A UV Index reading of 6 to 7 represents a high health risk from exposure to the Sun's UV radiation for average individuals.
Note: The daily maximum UV index of 7 in September interpret into the following advice:
Take precautions against overexposure. Protection against sun damage is needed. 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. On bright days sunglasses that block both UVA and UVB rays should be worn. A hat with a wide brim is extremely helpful, as it can prevent roughly 50% of UV radiation from reaching the eyes. Beware! The reflection of water and sand dramatically increases exposure to the UV rays.
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FAQ

What is the warmest month in Honolulu?

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

What is the temperature in September in Honolulu?

In September, in Honolulu, Hawaii, the average high-temperature is 81.5°F (27.5°C), and the average low-temperature is 75.6°F (24.2°C). The average heat index (a.k.a. 'apparent temperature', 'real feel'), which combines relative humidity and air temperature, in September is computed to be 86.4°F (30.2°C).

What are the least humid months in Honolulu?

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

What is the average humidity in September in Honolulu?

The average relative humidity in September is 74%.

How much does it rain in Honolulu in September?

In Honolulu, Hawaii, in September, it is raining for 17.9 days, with typically 1.22" (31mm) of accumulated precipitation.

What is the month with the warmest ocean in Honolulu?

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

What is the ocean temperature in September in Honolulu?

In Honolulu, Hawaii, the average seawater temperature in September 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?

In Honolulu, the average day length in September is 12h and 15min.

When are sunrise and sunset in September in Honolulu?

On the first day of September in Honolulu, Hawaii, sunrise is at 6:15 am and sunset at 6:47 pm. On the last day of the month, sunrise is at 6:22 am and sunset at 6:20 pm HST.

How many hours of sunshine does Honolulu have in September?

The average sunshine duration in September is 8.9h.

When is the highest UV index in Honolulu?

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

What is the UV index intensity in September in Honolulu?

The average daily maximum UV index in September in Honolulu is 7. A UV Index reading of 6 to 7 represents a high health vulnerability from exposure to Sun's UV rays.

Average temperature in September
Honolulu, HI

Average temperature in September - Honolulu, HI
  • Average high temperature in September: 81.5°F

The warmest month (with the highest average high temperature) is September (81.5°F).
The months with the lowest average high temperature are February and March (75°F).

  • Average low temperature in September: 75.6°F

The month with the highest average low temperature is August (75.7°F).
The coldest month (with the lowest average low temperature) is February (69.1°F).

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Average pressure in September
Honolulu, HI

Average pressure in September - Honolulu, HI
  • Average pressure in September: 29.97"Hg

The month with the highest atmospheric pressure is April (30.06"Hg).
The months with the lowest atmospheric pressure are September and October (29.97"Hg).

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Average wind speed in September
Honolulu, HI

Average wind speed in September - Honolulu, HI
  • Average wind speed in September: 9.9mph

The windiest month (with the highest average wind speed) is July (12.1mph).
The calmest month (with the lowest average wind speed) is January (9mph).

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Average humidity in September
Honolulu, HI

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

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

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Average rainfall in September
Honolulu, HI

Average rainfall in September - Honolulu, HI
  • Average rainfall in September: 1.22"

The wettest months (with the highest rainfall) are March and October (1.81").
The driest month (with the least rainfall) is July (0.67").

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Average rainfall days in September
Honolulu, HI

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

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

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Average sea temperature in September
Honolulu, HI

Average sea temperature in September - Honolulu, HI
  • Average sea temperature in September: 80.4°F

The best month for swimming (with the highest average sea temperature) is September (80.4°F).
The coldest month (with the lowest average sea temperature) is March (75.7°F).

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Average daylight in September /
Average sunshine in September
Honolulu, HI

Average daylight in September / Average sunshine in September - Honolulu, HI
  • Average daylight in September: 12h and 15min

The month with the longest days is June (Average daylight: 13h and 25min).
The month with the shortest days is December (Average daylight: 10h and 52min).

  • Average sunshine in September: 8h and 54min

The month with the most sunshine is June (Average sunshine: 10h and 48min).
The months with the least sunshine are November and December (Average sunshine: 6h and 30min).

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Average sunshine days in September
Honolulu, HI

Average sunshine days in September - Honolulu, HI
  • Average sunshine days in September: 6.9 days

The month with the most sunshine days is January (12.8 days).
The month with the least sunshine days is October (6.3 days).

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Average UV index in September
Honolulu, HI

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

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

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Average cloud cover in September
Honolulu, HI

Average cloud cover in September - Honolulu, HI
  • Average cloud cover in September: 33

The month with the most cloud cover is March (Cloud cover 40).
The months with the least cloud cover are January and September (Cloud cover 33).

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Average visibility in September
Honolulu, HI

Average visibility in September - Honolulu, HI
  • Average visibility in September: 6mi

The months with the highest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
The months with the lowest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).

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