Bothell, United States — Weather in September 2026

Monthly climate averages for Bothell, United States. Based on 10-year ERA5 reanalysis data.

Csb Warm-Summer Mediterranean
8.3 /10
Excellent

September is an excellent month in Bothell

Climate Overview

Bothell, United States in September has warm conditions, with highs averaging 21.2°C (70°F).

This month falls at the beginning of Autumn.

Daily highs in September gradually drop from around 24°C (76°F) at the start to 19°C (66°F) by month's end.

Rainfall is heaviest during the last third of the month, while the first third tends to be drier.

Expect around 10.8h of sunshine at the start of September, decreasing to 9.0h by the end.

The warmest days tend to fall around the 5th, averaging 24.5°C (76°F).

Compared to August, this month is about 4°C cooler with 4 more rainy days. Temperatures begin dropping heading into October.

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Monthly September Averages

Temperature
21°C / 13°C
Feels Like
21°C / 12°C
Rain
9 days · 73 mm
Sunshine
9.6h / day
Humidity
77% — Humid
Wind
14 km/h
Wind Direction
ENE (78°)
Gusts
27 km/h
Daylight
12.6 h
Cloud Cover
54%
Clear Sky Days
5.2
UV Index
4.6 — Moderate
Dew Point
13°C — Comfortable
Moon Phase
Waxing Crescent · 11%

Climate Charts

Daily averages based on historical data (2016–2025)

Daily Temperature

32°C 28°C 24°C 20°C 16°C 12°C 8°C 4°C 151015202530
HighLow

Daily Precipitation

0 mm 2 mm 4 mm 6 mm 8 mm 151015202530
Rainfall

Daily Sunshine

0h 3h 6h 9h 12h 151015202530
Sunshine

Daily Wind Speed

0 5 10 15 20 25 151015202530
Wind Speed
Sun Position
Sunrise 06:47
Daylight 12.6h
Sunset 19:23

What to Expect

Daytime temperatures around 21°C (70°F) are ideal for full-day outdoor exploration.

Rain usually comes in shorter passing showers rather than all-day rain.

2 of the last 5 yearly records were warmer than this month's long-run average.

Compare Months

January
Wet
Temp
8°C / 3°C
Feels Like
5°C / -1°C
Rain
18days (184 mm) Wet
Sun
4.3h Fair
Humidity
84% Humid
UV
1.2 Low
Snow Days
3days
View Details
February
Poor
Temp
8°C / 2°C
Feels Like
5°C / -1°C
Rain
17days (147 mm) Wet
Sun
5.4h Fair
Humidity
83% Humid
UV
2 Low
Snow Days
6days
View Details
March
Poor
Temp
11°C / 4°C
Feels Like
8°C / 0°C
Rain
17days (129 mm) Wet
Sun
7.6h Good
Humidity
81% Humid
UV
3.4 Moderate
Snow Days
2days
View Details
April
Fair
Temp
14°C / 6°C
Feels Like
12°C / 3°C
Rain
16days (107 mm) Wet
Sun
9.4h Good
Humidity
77% Humid
UV
4.7 Moderate
Snow Days
1days
View Details
May
Good
Temp
18°C / 9°C
Feels Like
17°C / 7°C
Rain
12days (79 mm) Wet
Sun
11h Excellent
Humidity
76% Humid
UV
5.5 High
View Details
June best
Excellent
Temp
21°C / 12°C
Feels Like
21°C / 11°C
Rain
10days (70 mm) Wet
Sun
11.7h Excellent
Humidity
74% Muggy
UV
6.3 High
View Details
July best
Excellent
Temp
25°C / 14°C
Feels Like
25°C / 15°C
Rain
5days (21 mm) Good
Sun
12.7h Excellent
Humidity
70% Muggy
UV
6.9 High
View Details
August best
Excellent
Temp
25°C / 15°C
Feels Like
26°C / 15°C
Rain
5days (31 mm) Good
Sun
11.5h Excellent
Humidity
71% Muggy
UV
5.8 High
View Details
September best
Excellent
Temp
21°C / 13°C
Feels Like
21°C / 12°C
Rain
9days (73 mm) Wet
Sun
9.6h Good
Humidity
77% Humid
UV
4.6 Moderate
View Details
October
Fair
Temp
15°C / 9°C
Feels Like
14°C / 6°C
Rain
16days (151 mm) Wet
Sun
7h Good
Humidity
83% Humid
UV
2.9 Moderate
View Details
November
Wet
Temp
10°C / 6°C
Feels Like
8°C / 3°C
Rain
19days (189 mm) Wet
Sun
4.6h Fair
Humidity
85% Humid
UV
1.6 Low
Snow Days
1days
View Details
December
Wet
Temp
7°C / 3°C
Feels Like
4°C / 0°C
Rain
19days (205 mm) Wet
Sun
3.5h Poor
Humidity
85% Humid
UV
1 Low
Snow Days
3days
View Details
Month Temp Feels Like Rain Sun Humidity UV Status
January 8°C / 3°C 5°C / -1°C 18days (184 mm) Wet 4.3h Fair 84% Humid 1.2 Low Wet View Details
February 8°C / 2°C 5°C / -1°C 17days (147 mm) Wet 5.4h Fair 83% Humid 2 Low Poor View Details
March 11°C / 4°C 8°C / 0°C 17days (129 mm) Wet 7.6h Good 81% Humid 3.4 Moderate Poor View Details
April 14°C / 6°C 12°C / 3°C 16days (107 mm) Wet 9.4h Good 77% Humid 4.7 Moderate Fair View Details
May 18°C / 9°C 17°C / 7°C 12days (79 mm) Wet 11h Excellent 76% Humid 5.5 High Good View Details
June best 21°C / 12°C 21°C / 11°C 10days (70 mm) Wet 11.7h Excellent 74% Muggy 6.3 High Excellent View Details
July best 25°C / 14°C 25°C / 15°C 5days (21 mm) Good 12.7h Excellent 70% Muggy 6.9 High Excellent View Details
August best 25°C / 15°C 26°C / 15°C 5days (31 mm) Good 11.5h Excellent 71% Muggy 5.8 High Excellent View Details
September best 21°C / 13°C 21°C / 12°C 9days (73 mm) Wet 9.6h Good 77% Humid 4.6 Moderate Excellent View Details
October 15°C / 9°C 14°C / 6°C 16days (151 mm) Wet 7h Good 83% Humid 2.9 Moderate Fair View Details
November 10°C / 6°C 8°C / 3°C 19days (189 mm) Wet 4.6h Fair 85% Humid 1.6 Low Wet View Details
December 7°C / 3°C 4°C / 0°C 19days (205 mm) Wet 3.5h Poor 85% Humid 1 Low Wet View Details

What to Wear

Dress in layers — a mix of long sleeves, light sweaters, and a versatile jacket works best for changeable conditions.

A waterproof jacket or compact umbrella is recommended for occasional showers.

Packing List

UmbrellaSunscreen (SPF 30+)SunglassesComfortable walking shoes

Frequently Asked Questions

September is typically excellent for visiting Bothell, with average highs of 21°C (70°F) and around 9 rainy days. Bothell, United States in September has warm conditions, with highs averaging 21.2°C (70°F).
Bothell typically sees around 9 rainy days in September with 73 mm (2.9 in) of total rainfall. An umbrella should suffice.
Evenings in Bothell during September are mild at 13°C (55°F). A light cardigan is usually enough.
With highs of 21°C (70°F) and lows of 13°C (55°F) in September, we recommend: Umbrella, Sunscreen (SPF 30+), Sunglasses, Comfortable walking shoes. Comfortable walking shoes are essential.
Yes, September offers some of the best weather conditions in Bothell with comfortable temperatures and lower chances of rain.
The average UV index in Bothell during September is 5 (moderate). Sunscreen and sunglasses are recommended during midday hours.
Bothell gets approximately 13 hours of daylight per day in September, with around 10 hours of sunshine.
Snow is uncommon in Bothell during September based on 10-year climate averages.

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