September weather forecast and climate
Half Moon Bay, CA

A warm and sunny day on a scenic beach in Half Moon Bay, California
A warm and sunny day on a scenic beach in Half Moon Bay, California

Weather in September

September, the first month of the autumn, in Half Moon Bay, is still a comfortable month, with average temperature ranging between min 56.7°F (13.7°C) and max 66.9°F (19.4°C).

Temperature

The warmest month is September, with an average high-temperature of 66.9°F (19.4°C) and an average low-temperature of 56.7°F (13.7°C).

Humidity

In September, the average relative humidity is 77%.

Rainfall

In Half Moon Bay, in September, it is raining for 3.6 days, with typically 0.16" (4mm) of accumulated precipitation. Throughout the year, in Half Moon Bay, there are 76.8 rainfall days, and 8.54" (217mm) of precipitation is accumulated.

Daylight

In September, the average length of the day is 12.4h.

Sunshine

In Half Moon Bay, the average sunshine in September is 10.7h.

UV index

June, August and September, with an average maximum UV index of 5, are months with the highest UV index. A UV Index of 3 to 5 symbolizes a medium health hazard from the exposure to the Sun's UV rays for the ordinary person.
Note: The average daily UV index of 5 in September transform into the following instructions:
Take precautions - Protection against the skin and eye damage is obliged. The solar radiation is most powerful near the mid-day, so the exposure to the direct Sun should be reduced accordingly. A wide-brim hat offers excellent sun protection for eyes, ears, face, and neck. Sunglasses with UVA and UVB protection significantly reduce eye damage from sun exposure. Tightly woven, loose-fitting clothes provide additional protection from the Sun.
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FAQ

What is the warmest month in Half Moon Bay?

With an average high-temperature of 66.9°F (19.4°C) and an average low-temperature of 56.7°F (13.7°C), September is the warmest month in Half Moon Bay, California.

What is the temperature in September in Half Moon Bay?

The average high-temperature, in September, is 66.9°F (19.4°C), while the average low-temperature is 56.7°F (13.7°C).

What is the average humidity in September in Half Moon Bay?

The average relative humidity in September in Half Moon Bay, California, is 77%.

How much does it rain in Half Moon Bay in September?

In Half Moon Bay, California, in September, it is raining for 3.6 days, with typically 0.16" (4mm) of accumulated precipitation.

What is the average length of the day in September in Half Moon Bay?

The average length of the day in September is 12.4h.

How many hours of sunshine does Half Moon Bay have in September?

In Half Moon Bay, the average sunshine in September is 10.7h.

What is the month with the highest UV index in Half Moon Bay?

June, August and September, with an average maximum UV index of 5, are months with the highest UV index in Half Moon Bay, California.

What is the UV index intensity in September in Half Moon Bay?

In Half Moon Bay, the average daily maximum UV index in September is 5. A UV Index estimate of 3 to 5 represents a medium health risk from unprotected exposure to the UV radiation.

Average temperature in September
Half Moon Bay, CA

Average temperature in September - Half Moon Bay, CA
  • Average high temperature in September: 66.9°F

The warmest month (with the highest average high temperature) is September (66.9°F).
The month with the lowest average high temperature is December (55.6°F).

  • Average low temperature in September: 56.7°F

The month with the highest average low temperature is September (56.7°F).
The coldest month (with the lowest average low temperature) is February (48.7°F).

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Average pressure in September
Half Moon Bay, CA

Average pressure in September - Half Moon Bay, CA
  • Average pressure in September: 29.92"

The month with the highest atmospheric pressure is January (30.13").
The month with the lowest atmospheric pressure is September (29.92").

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Average wind speed in September
Half Moon Bay, CA

Average wind speed in September - Half Moon Bay, CA
  • Average wind speed in September: 7mph

The windiest month (with the highest average wind speed) is April (9.6mph).
The calmest month (with the lowest average wind speed) is August (6.6mph).

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Average humidity in September
Half Moon Bay, CA

Average humidity in September - Half Moon Bay, CA
  • Average humidity in September: 77%

The month with the highest relative humidity is August (82%).
Months with the lowest relative humidity are November and December (72%).

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Average rainfall in September
Half Moon Bay, CA

Average rainfall in September - Half Moon Bay, CA
  • Average rainfall in September: 0.16"

The wettest month (with the highest rainfall) is February (1.61").
The driest months (with the least rainfall) are June and July (0.12").

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Average rainfall days in September
Half Moon Bay, CA

Average rainfall days in September - Half Moon Bay, CA
  • Average rainfall days in September: 3.6 days

The month with the highest number of rainy days is March (10.8 days).
The month with the least rainy days is June (3 days).

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Average daylight in September /
Average sunshine in September
Half Moon Bay, CA

Average daylight in September / Average sunshine in September - Half Moon Bay, CA
  • Average daylight in September: 12.4h

The month with the longest days is June (Average daylight: 14.7h).
The month with the shortest days is December (Average daylight: 9.6h).

  • Average sunshine in September: 10.7h

The month with the most sunshine is July (Average sunshine: 11.4h).
The month with the least sunshine is December (Average sunshine: 5.7h).

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Average sunshine days in September
Half Moon Bay, CA

Average sunshine days in September - Half Moon Bay, CA
  • Average sunshine days in September: 22.6 days

The month with the most sunshine days is October (24.6 days).
Months with the least sunshine days are March and August (18.8 days).

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Average UV index in September
Half Moon Bay, CA

Average UV index in September - Half Moon Bay, CA
  • Average UV index in September: 5

Months with the highest UV index are June, August and September (UV index 5).
Months with the lowest UV index are January, February, March, April, May, July, October, November and December (UV index 4).

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Average cloud cover in September
Half Moon Bay, CA

Average cloud cover in September - Half Moon Bay, CA
  • Average cloud cover in September: 18

The month with the most cloud cover is March (Cloud cover 38).
The month with the least cloud cover is September (Cloud cover 18).

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Average visibility in September
Half Moon Bay, CA

Average visibility in September - Half Moon Bay, CA
  • 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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