September weather forecast and climate
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 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

The average heat index is estimated at a hot 86.4°F (30.2°C). Constant exposure and activity lead to possible fatigue. Prolonged exercise 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 'apparent temperature', 'real feel', 'feels like', or 'felt air temperature', is a measure that combines both air temperature and relative humidity into a single value that indicates how hot the weather feels. Additional factors like clothing, differences in body mass, height, and shape, metabolic differences, and activity influence one's weather impression. Be aware that direct exposure to sunlight increases heat impact, and may raise the heat index additionally, 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.

Rainfall

In September, in Honolulu, the rain falls for 17.9 days. Throughout September, 1.22" (31mm) of precipitation is accumulated. Throughout the year, in Honolulu, 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.
Note: 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.

Daylight

The average length of the day is 12.3h.

Sunshine

The average sunshine in September is 8.9h.

UV index

July through September, with an average maximum UV index of 7, are months with the highest UV index in Honolulu, Hawaii. A UV Index of 6 to 7 symbolizes a high health risk from unsafe exposure to the UV radiation for ordinary 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. Seek shade and minimize exposure to direct Sun in a period between 10 a.m. and 4 p.m. when UV radiation is most intense; keep in mind that shade structures like parasols or canopies do not provide perfect sun protection. 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. Beware! The strength of the UV rays is significantly increased by the reflection of the water and sand.
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FAQ

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, Hawaii.

What is the temperature in September in Honolulu?

The average high-temperature, in September, 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. 'real feel', 'apparent temperature'), that calculates temperature value influenced by the moisture in the air, in September is evaluated at 86.4°F (30.2°C).

What are the least humid months in Honolulu?

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

What is the average humidity in September in Honolulu?

The average relative humidity in September in Honolulu, Hawaii, is 74%.

How many days does it rain in September in Honolulu?

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

When is the ocean warmest in Honolulu?

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

What is the water temperature in September in Honolulu?

In Honolulu, Hawaii, in September, the average water temperature is 80.4°F (26.9°C). 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.

How many hours of daylight does Honolulu have in September?

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

How long on average sun shines in September in Honolulu?

In Honolulu, Hawaii, the average sunshine in September is 8.9h.

What is the month 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 in Honolulu, Hawaii.

How high is the UV index 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 risk from the exposure to the 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).
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"

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

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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%

Months with the highest relative humidity are February and December (76%).
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

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: 12.3h

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

  • Average sunshine in September: 8.9h

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

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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

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).

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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).
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

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

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