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September Weather in San Juan Puerto Rico

Daily high temperatures are around 88°F, rarely falling below 86°F or exceeding 91°F.

Daily low temperatures are around 77°F, rarely falling below 75°F or exceeding 80°F.

For reference, on August 20, the hottest day of the year, temperatures in San Juan typically range from 78°F to 89°F, while on January 25, the coldest day of the year, they range from 72°F to 83°F.

Average High and Low Temperature in September in San Juan

The daily average high (red line) and low (blue line) temperature, with 25th to 75th and 10th to 90th percentile bands. The thin dotted lines are the corresponding average perceived temperatures.

The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on September. The horizontal axis is the day, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.

Average Hourly Temperature in September in San Juan

Average Hourly Temperature in September in San JuanSep11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303012 AM12 AM2 AM2 AM4 AM4 AM6 AM6 AM8 AM8 AM10 AM10 AM12 PM12 PM2 PM2 PM4 PM4 PM6 PM6 PM8 PM8 PM10 PM10 PM12 AM12 AMAugOctNowNowwarmwarmhot
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
The average hourly temperature, color coded into bands. The shaded overlays indicate night and civil twilight.

Mombasa, Kenya (7,348 miles away) is the far-away foreign place with temperatures most similar to San Juan (view comparison).

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The month of September in San Juan experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 68% throughout the month. The highest chance of overcast or mostly cloudy conditions is 69% on September 25.

The clearest day of the month is September 3, with clear, mostly clear, or partly cloudy conditions 34% of the time.

For reference, on May 29, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 73%, while on January 11, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 82%.

Cloud Cover Categories in September in San Juan

Cloud Cover Categories in September in San JuanSep1122334455667788991010111112121313141415151616171718181919202021212222232324242525262627272828292930300%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%AugOctJan 1182%Jan 1182%Sep 134%Sep 134%Sep 3032%Sep 3032%Sep 1132%Sep 1132%Sep 2132%Sep 2132%NowNowclearmostly clearpartly cloudymostly cloudyovercast
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds.

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In San Juan, the chance of a wet day over the course of September is essentially constant, remaining around 49% throughout.

For reference, the year's highest daily chance of a wet day is 50% on September 25, and its lowest chance is 20% on January 9.

Probability of Precipitation in September in San Juan

Probability of Precipitation in September in San JuanSep1122334455667788991010111112121313141415151616171718181919202021212222232324242525262627272828292930300%0%5%5%10%10%15%15%20%20%25%25%30%30%35%35%40%40%45%45%50%50%55%55%AugOctSep 2550%Sep 2550%Sep 148%Sep 148%Sep 1150%Sep 1150%NowNowrain
The percentage of days in which various types of precipitation are observed, excluding trace quantities: rain alone, snow alone, and mixed (both rain and snow fell in the same day).

Rainfall

To show variation within the month and not just the monthly total, we show the rainfall accumulated over a sliding 31-day period centered around each day.

The average sliding 31-day rainfall during September in San Juan is gradually increasing, starting the month at 4.2 inches, when it rarely exceeds 8.4 inches or falls below 1.1 inches, and ending the month at 4.6 inches, when it rarely exceeds 8.5 inches or falls below 1.2 inches.

The highest average 31-day accumulation is 4.8 inches on September 17.

Average Monthly Rainfall in September in San Juan

The average rainfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average snowfall.

Over the course of September in San Juan, the length of the day is gradually decreasing. From the start to the end of the month, the length of the day decreases by 30 minutes, implying an average daily decrease of 1 minute, 2 seconds, and weekly decrease of 7 minutes, 12 seconds.

The shortest day of the month is September 30, with 11 hours, 58 minutes of daylight and the longest day is September 1, with 12 hours, 28 minutes of daylight.

Hours of Daylight and Twilight in September in San Juan

Hours of Daylight and Twilight in September in San JuanSep1122334455667788991010111112121313141415151616171718181919202021212222232324242525262627272828292930300 hr24 hr4 hr20 hr8 hr16 hr12 hr12 hr16 hr8 hr20 hr4 hr24 hr0 hrAugOctSep 2212 hr, 8 minSep 2212 hr, 8 minnightnightdaydaySep 112 hr, 28 minSep 112 hr, 28 minNowNow
The number of hours during which the Sun is visible (black line). From bottom (most yellow) to top (most gray), the color bands indicate: full daylight, twilight (civil, nautical, and astronomical), and full night.

The earliest sunrise of the month in San Juan is 6:09 AM on September 1 and the latest sunrise is 5 minutes later at 6:14 AM on September 30.

The latest sunset is 6:38 PM on September 1 and the earliest sunset is 25 minutes earlier at 6:13 PM on September 30.

Daylight saving time is not observed in San Juan during 2024.

For reference, on June 20, the longest day of the year, the Sun rises at 5:48 AM and sets 13 hours, 14 minutes later, at 7:03 PM, while on December 21, the shortest day of the year, it rises at 6:52 AM and sets 11 hours, 1 minute later, at 5:53 PM.

Sunrise & Sunset with Twilight in September in San Juan

Sunrise & Sunset with Twilight in September in San JuanSep1122334455667788991010111112121313141415151616171718181919202021212222232324242525262627272828292930302 AM4 AM6 AM8 AM10 AM12 PM2 PM4 PM6 PM8 PM10 PM12 AMAugOct6:09 AM6:09 AMSep 16:38 PMSep 16:38 PM6:14 AM6:14 AMSep 306:13 PMSep 306:13 PM6:11 AM6:11 AMSep 116:29 PMSep 116:29 PMSolarMidnightSolarMidnightSolarNoonSunriseSunsetNowNow
The solar day over the course of September. From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray.

The figure below presents a compact representation of the sun's elevation (the angle of the sun above the horizon) and azimuth (its compass bearing) for every hour of every day in the reporting period. The horizontal axis is the day of the year and the vertical axis is the hour of the day. For a given day and hour of that day, the background color indicates the azimuth of the sun at that moment. The black isolines are contours of constant solar elevation.

Solar Elevation and Azimuth in September in San Juan

Solar Elevation and Azimuth in September in San JuanSep11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303012 AM12 AM2 AM2 AM4 AM4 AM6 AM6 AM8 AM8 AM10 AM10 AM12 PM12 PM2 PM2 PM4 PM4 PM6 PM6 PM8 PM8 PM10 PM10 PM12 AM12 AMAugOct0010102020203030404050505060607080000101020203030304040505060607080NowNow
northeastsouthwest
Solar elevation and azimuth over the course of September 2024. The black lines are lines of constant solar elevation (the angle of the sun above the horizon, in degrees). The background color fills indicate the azimuth (the compass bearing) of the sun. The lightly tinted areas at the boundaries of the cardinal compass points indicate the implied intermediate directions (northeast, southeast, southwest, and northwest).

The figure below presents a compact representation of key lunar data for September 2024. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases. The label associated with each bar indicates the date and time that the phase is obtained, and the companion time labels indicate the rise and set times of the Moon for the nearest time interval in which the moon is above the horizon.

Moon Rise, Set & Phases in September in San Juan

Moon Rise, Set & Phases in September in San JuanSep11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303012 AM12 AM4 AM4 AM8 AM8 AM12 PM12 PM4 PM4 PM8 PM8 PM12 AM12 AMAugOctAug 47:14 AMAug 47:14 AMAug 192:26 PMAug 192:26 PMSep 29:56 PMSep 29:56 PMSep 1710:35 PMSep 1710:35 PMOct 22:50 PMOct 22:50 PMOct 177:27 AMOct 177:27 AM6:03 AM6:03 AM7:24 PM7:24 PM7:02 PM7:02 PM6:52 AM6:52 AM5:42 AM5:42 AM6:35 PM6:35 PM6:16 PM6:16 PM6:36 AM6:36 AM6:02 AM6:02 AM6:11 PM6:11 PM5:28 PM5:28 PM6:19 AM6:19 AMNowNow
The time in which the moon is above the horizon (light blue area), with new moons (dark gray lines) and full moons (blue lines) indicated. The shaded overlays indicate night and civil twilight.
Sep 2024IlluminationMoonriseMoonsetMoonriseMeridian PassingDistance
1
2%4:51 AMENE6:01 PMWNW-11:28 AMS249,093 mi
2
0%5:42 AMENE6:35 PMW-12:10 PMS250,507 mi
3
0%6:31 AME7:07 PMW-12:50 PMS251,562 mi
4
2%7:18 AME7:38 PMW-1:29 PMS252,215 mi
5
6%8:05 AME8:09 PMW-2:07 PMS252,402 mi
6
12%8:52 AME8:41 PMWSW-2:46 PMS252,050 mi
7
19%9:40 AMESE9:15 PMWSW-3:27 PMS251,083 mi
8
27%10:31 AMESE9:53 PMWSW-4:12 PMS249,444 mi
9
37%11:24 AMESE10:36 PMWSW-5:00 PMS247,109 mi
10
47%12:20 PMESE11:25 PMWSW-5:52 PMS244,108 mi
11
50%1:18 PMESE--6:49 PMS240,542 mi
12
68%-12:19 AMWSW2:15 PMESE7:48 PMS236,597 mi
13
78%-1:19 AMWSW3:11 PMESE8:47 PMS232,545 mi
14
87%-2:22 AMWSW4:02 PMESE9:45 PMS228,725 mi
15
94%-3:27 AMWSW4:50 PMESE10:41 PMS225,501 mi
16
99%-4:31 AMWSW5:34 PMESE11:34 PMS223,208 mi
17
100%-5:34 AMW6:16 PME--
18
100%-6:36 AMW6:57 PME12:25 AMS222,093 mi
19
98%-7:38 AMW7:39 PMENE1:16 AMS222,270 mi
20
93%-8:41 AMWNW8:23 PMENE2:08 AMS223,695 mi
21
86%-9:45 AMWNW9:11 PMENE3:02 AMN226,180 mi
22
76%-10:50 AMWNW10:03 PMENE3:58 AMN229,433 mi
23
65%-11:54 AMWNW10:59 PMENE4:57 AMN233,114 mi
24
50%-12:55 PMWNW11:57 PMENE5:57 AMN236,895 mi
25
43%-1:51 PMWNW-6:55 AMN240,502 mi
26
33%12:56 AMENE2:40 PMWNW-7:50 AMN243,740 mi
27
23%1:53 AMENE3:24 PMWNW-8:40 AMN246,495 mi
28
15%2:47 AMENE4:02 PMWNW-9:27 AMN248,718 mi
29
9%3:38 AMENE4:37 PMWNW-10:10 AMS250,410 mi
30
4%4:27 AME5:09 PMW-10:50 AMS251,598 mi

We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.

The chance that a given day will be muggy in San Juan is essentially constant during September, remaining around 100% throughout.

For reference, on June 11, the muggiest day of the year, there are muggy conditions 100% of the time, while on March 8, the least muggy day of the year, there are muggy conditions 81% of the time.

Humidity Comfort Levels in September in San Juan

Humidity Comfort Levels in September in San JuanSep1122334455667788991010111112121313141415151616171718181919202021212222232324242525262627272828292930300%0%10%10%20%20%30%30%40%40%50%50%60%60%70%70%80%80%90%90%100%100%AugOctSep 1100%Sep 1100%Sep 30100%Sep 30100%Sep 11100%Sep 11100%Sep 21100%Sep 21100%NowNowmiserablemiserableoppressiveoppressivemuggymuggy
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
The percentage of time spent at various humidity comfort levels, categorized by dew point.

This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.

The average hourly wind speed in San Juan is decreasing during September, decreasing from 10.8 miles per hour to 9.5 miles per hour over the course of the month.

For reference, on July 13, the windiest day of the year, the daily average wind speed is 12.5 miles per hour, while on October 9, the calmest day of the year, the daily average wind speed is 9.3 miles per hour.

Average Wind Speed in September in San Juan

Average Wind Speed in September in San JuanSep1122334455667788991010111112121313141415151616171718181919202021212222232324242525262627272828292930300 mph0 mph2 mph2 mph4 mph4 mph6 mph6 mph8 mph8 mph10 mph10 mph12 mph12 mph14 mph14 mphAugOctSep 110.8 mphSep 110.8 mphSep 309.5 mphSep 309.5 mphSep 1610.0 mphSep 1610.0 mphNowNow
The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.

The hourly average wind direction in San Juan throughout September is predominantly from the east, with a peak proportion of 89% on September 1.

Wind Direction in September in San Juan

Wind Direction in September in San JuanSep1122334455667788991010111112121313141415151616171718181919202021212222232324242525262627272828292930300%100%20%80%40%60%60%40%80%20%100%0%AugOctNowNoweastsouth
northeastsouthwest
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions, excluding hours in which the mean wind speed is less than 1.0 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

San Juan is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.

The average surface water temperature in San Juan is essentially constant during September, remaining around 84°F throughout.

The highest average surface water temperature during September is 84°F on September 26.

Average Water Temperature in September in San Juan

Average Water Temperature in September in San JuanSep11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303081.0°F81.0°F81.5°F81.5°F82.0°F82.0°F82.5°F82.5°F83.0°F83.0°F83.5°F83.5°F84.0°F84.0°F84.5°F84.5°F85.0°F85.0°F85.5°F85.5°FAugOctSep 2684°FSep 2684°FSep 184°FSep 184°FSep 1184°FSep 1184°FNowNow
The daily average water temperature (purple line), with 25th to 75th and 10th to 90th percentile bands.

Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).

Temperatures in San Juan are sufficiently warm year round that it is not entirely meaningful to discuss the growing season in these terms. We nevertheless include the chart below as an illustration of the distribution of temperatures experienced throughout the year.

Time Spent in Various Temperature Bands and the Growing Season in September in San Juan

Time Spent in Various Temperature Bands and the Growing Season in September in San JuanSep1122334455667788991010111112121313141415151616171718181919202021212222232324242525262627272828292930300%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%AugOct100%Sep 16100%Sep 16NowNowwarmhotcomfortable
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
The percentage of time spent in various temperature bands. The black line is the percentage chance that a given day is within the growing season.

Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.

The average accumulated growing degree days in San Juan are very rapidly increasing during September, increasing by 922°F, from 7,222°F to 8,143°F, over the course of the month.

Growing Degree Days in September in San Juan

Growing Degree Days in September in San JuanSep1122334455667788991010111112121313141415151616171718181919202021212222232324242525262627272828292930307,200°F7,200°F7,400°F7,400°F7,600°F7,600°F7,800°F7,800°F8,000°F8,000°F8,200°F8,200°FAugOctSep 17,222°FSep 17,222°FSep 308,143°FSep 308,143°FSep 117,538°FSep 117,538°FSep 217,862°FSep 217,862°FNowNow
The average growing degree days accumulated over the course of September, with 25th to 75th and 10th to 90th percentile bands.

This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.

The average daily incident shortwave solar energy in San Juan is gradually decreasing during September, falling by 0.6 kWh, from 5.3 kWh to 4.8 kWh, over the course of the month.

Average Daily Incident Shortwave Solar Energy in September in San Juan

Average Daily Incident Shortwave Solar Energy in September in San JuanSep1122334455667788991010111112121313141415151616171718181919202021212222232324242525262627272828292930300 kWh0 kWh1 kWh1 kWh2 kWh2 kWh3 kWh3 kWh4 kWh4 kWh5 kWh5 kWh6 kWh6 kWh7 kWh7 kWh8 kWh8 kWhAugOctSep 15.3 kWhSep 15.3 kWhSep 304.8 kWhSep 304.8 kWhSep 115.1 kWhSep 115.1 kWhNowNow
The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.

For the purposes of this report, the geographical coordinates of San Juan are 18.466 deg latitude, -66.106 deg longitude, and 36 ft elevation.

The topography within 2 miles of San Juan contains only modest variations in elevation, with a maximum elevation change of 194 feet and an average elevation above sea level of 5 feet. Within 10 miles contains only modest variations in elevation (984 feet). Within 50 miles contains very significant variations in elevation (4,390 feet).

The area within 2 miles of San Juan is covered by water (78%) and artificial surfaces (19%), within 10 miles by water (58%) and grassland (16%), and within 50 miles by water (75%) and trees (14%).

This report illustrates the typical weather in San Juan, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.

Temperature and Dew Point

There are 2 weather stations near enough to contribute to our estimation of the temperature and dew point in San Juan.

For each station, the records are corrected for the elevation difference between that station and San Juan according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.

The estimated value at San Juan is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between San Juan and a given station.

The stations contributing to this reconstruction are:

To get a sense of how much these sources agree with each other, you can view a comparison of San Juan and the stations that contribute to our estimates of its temperature history and climate. Please note that each source's contribution is adjusted for elevation and the relative change present in the MERRA-2 data.

Other Data

All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Algorithms 2nd Edition , by Jean Meeus.

All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.

Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.

Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.

Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .

Time zones for airports and weather stations are provided by AskGeo.com .

Maps are © OpenStreetMap contributors.

Disclaimer

The information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site.

We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands.

We further caution that our travel scores are only as good as the data that underpin them, that weather conditions at any given location and time are unpredictable and variable, and that the definition of the scores reflects a particular set of preferences that may not agree with those of any particular reader.

Please review our full terms contained on our Terms of Service page.