San Juan County climate

San Juan County Weather in September

NOAA 1991-2020 normals for Friday Harbor AP, 1 km from San Juan County

Average highs run from 72°F on September 1 to 64°F on September 30, and lows from 49°F to 46°F. Normal precipitation for the month is 1.04 in over about 12 wet days.

September day by day

The normal high and low for each date, and the record, in °F.

Normal daily high and low temperature at San Juan County, in °F, with the record for each date.20406080100151015202530
  • Normal low
  • Normal high
  • Record high
  • Record low

September at a glance

Average high
68°F
Average low
48°F
Precipitation
1.04 in
Record high
89°FSep 3, 2017
Record low
36°FSep 23, 2000
Chance of a freeze
0%
Daylight
13 h 23 min to 11 h 43 min
Cloud cover
53%
Humidity
76%
Dew point
51°F
Wind
5.1 mph

Every day of the month

A wet day has at least 0.01 inch of precipitation; snow means at least 0.1 inch of snowfall.

DateNormal highNormal lowRecord highRecord lowChance wetChance of snow
Sep 172°F49°F81°F 202441°F 199932%0%
Sep 272°F49°F84°F 200640°F 199933%0%
Sep 371°F49°F89°F 201743°F 199933%0%
Sep 471°F49°F87°F 201742°F 200234%0%
Sep 571°F49°F85°F 202441°F 200234%0%
Sep 671°F49°F85°F 202441°F 200235%0%
Sep 771°F49°F82°F 201240°F 199935%0%
Sep 870°F49°F84°F 201144°F 200136%0%
Sep 970°F49°F83°F 202042°F 199836%0%
Sep 1070°F49°F86°F 202041°F 199937%0%
Sep 1170°F48°F85°F 201341°F 200037%0%
Sep 1269°F48°F78°F 200940°F 201238%0%
Sep 1369°F48°F80°F 199941°F 200338%0%
Sep 1469°F48°F78°F 201444°F 200338%0%
Sep 1569°F48°F81°F 201442°F 200139%0%
Sep 1668°F48°F81°F 202541°F 199939%0%
Sep 1768°F48°F78°F 201241°F 200240%0%
Sep 1868°F48°F75°F 200941°F 200540%0%
Sep 1967°F48°F79°F 199943°F 199840%0%
Sep 2067°F48°F77°F 202240°F 200241%0%
Sep 2167°F47°F76°F 202239°F 200241%0%
Sep 2266°F47°F78°F 200938°F 200042%0%
Sep 2366°F47°F76°F 201136°F 200042%0%
Sep 2466°F47°F73°F 202439°F 200043%0%
Sep 2565°F47°F74°F 202239°F 200043%0%
Sep 2665°F47°F76°F 202240°F 200043%0%
Sep 2765°F47°F77°F 200339°F 199944%0%
Sep 2864°F47°F81°F 200338°F 199944%0%
Sep 2964°F46°F74°F 201840°F 199944%0%
Sep 3064°F46°F72°F 202038°F 199945%0%

Chance of rain

The chance of at least 0.01 inch of precipitation on each date at San Juan County, in percent, and of at least 0.1 inch of snowfall.010203040501102030
  • Chance of a wet day
  • Chance of snowfall

Sunrise and sunset

Times for 2026, local time (PDT).

September 1
sunrise 6:30 AM, sunset 7:53 PM
September 30
sunrise 7:10 AM, sunset 6:53 PM

Every day of September: sun and moon

Other months

Sources

Normals: NOAA NCEI U.S. Climate Normals, 1991-2020, station USW00094276 (Friday Harbor AP), public domain. Records: NOAA GHCN-Daily, station USW00094276, every year on file, quality-flagged values removed. Cloud, humidity, wind and sunshine: NASA POWER (MERRA-2, CERES and GEWEX SRB), 1991-2020. The data was obtained from the National Aeronautics and Space Administration (NASA) Langley Research Center's Prediction Of Worldwide Energy Resources (POWER) project funded through the NASA Earth Science Division: POWER Daily API v2, accessed 2026-09-24. Sun and moon: computed with the NOAA solar equations and Meeus.