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Fall Weather in San Juan Puerto Rico

Daily high temperatures decrease by 4°F, from 88°F to 84°F, rarely falling below 82°F or exceeding 91°F.

Daily low temperatures decrease by 4°F, from 78°F to 74°F, rarely falling below 72°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 the Fall in San Juan

Average High and Low Temperature in the Fall in San JuanSepOctNov70°F70°F75°F75°F80°F80°F85°F85°F90°F90°F95°F95°F100°F100°FSummerWinterSep 188°FSep 188°F78°F78°FNov 3084°FNov 3084°F74°F74°FOct 188°FOct 188°F77°F77°FNov 187°FNov 187°F76°F76°FNowNow
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 fall temperatures. 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 the Fall in San Juan

Average Hourly Temperature in the Fall in San JuanSepOctNov12 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 AMSummerWinterNowNowcomfortablewarmhot
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 fall in San Juan experiences very rapidly decreasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy decreasing from 66% to 35%. The highest chance of overcast or mostly cloudy conditions is 69% on September 25.

The clearest day of the fall is November 30, with clear, mostly clear, or partly cloudy conditions 65% 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 the Fall in San Juan

Cloud Cover Categories in the Fall in San JuanSepOctNov0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%SummerWinterJan 1182%Jan 1182%Sep 134%Sep 134%Nov 3065%Nov 3065%Oct 132%Oct 132%Nov 142%Nov 142%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 the fall is very rapidly decreasing, starting the season at 48% and ending it at 36%.

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 the Fall in San Juan

Probability of Precipitation in the Fall in San JuanSepOctNov0%0%5%5%10%10%15%15%20%20%25%25%30%30%35%35%40%40%45%45%50%50%55%55%SummerWinterSep 2550%Sep 2550%Sep 148%Sep 148%Nov 3036%Nov 3036%Nov 149%Nov 149%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 season and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day.

The average sliding 31-day rainfall during the fall in San Juan is rapidly decreasing, starting the season at 4.2 inches, when it rarely exceeds 8.4 inches or falls below 1.1 inches, and ending the season at 2.9 inches, when it rarely exceeds 6.9 inches or falls below 0.4 inches.

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

Average Monthly Rainfall in the Fall in San Juan

Average Monthly Rainfall in the Fall in San JuanSepOctNov0 in0 in2 in2 in4 in4 in6 in6 in8 in8 in10 in10 inSummerWinterSep 174.8 inSep 174.8 inSep 14.2 inSep 14.2 inNov 302.9 inNov 302.9 inOct 14.5 inOct 14.5 inNov 14.4 inNov 14.4 inNowNow
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 the fall in San Juan, the length of the day is rapidly decreasing. From the start to the end of the season, the length of the day decreases by 1 hour, 22 minutes, implying an average daily decrease of 55 seconds, and weekly decrease of 6 minutes, 22 seconds.

The shortest day of the fall is November 30, with 11 hours, 6 minutes of daylight and the longest day is September 1, with 12 hours, 28 minutes of daylight.

Hours of Daylight and Twilight in the Fall in San Juan

Hours of Daylight and Twilight in the Fall in San JuanSepOctNov0 hr24 hr4 hr20 hr8 hr16 hr12 hr12 hr16 hr8 hr20 hr4 hr24 hr0 hrSummerWinterSep 2212 hr, 8 minSep 2212 hr, 8 minnightnightdaydayNov 3011 hr, 6 minNov 3011 hr, 6 minNov 111 hr, 27 minNov 111 hr, 27 min
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 fall in San Juan is 6:09 AM on September 1 and the latest sunrise is 30 minutes later at 6:40 AM on November 30.

The latest sunset is 6:38 PM on September 1 and the earliest sunset is 52 minutes earlier at 5:46 PM on November 24.

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 the Fall in San Juan

Sunrise & Sunset with Twilight in the Fall in San JuanSepOctNov2 AM4 AM6 AM8 AM10 AM12 PM2 PM4 PM6 PM8 PM10 PM12 AMSummerWinter6:09 AM6:09 AMSep 16:38 PMSep 16:38 PM6:36 AM6:36 AMNov 245:46 PMNov 245:46 PM6:15 AM6:15 AMOct 16:12 PMOct 16:12 PM6:24 AM6:24 AMNov 15:51 PMNov 15:51 PMSolarMidnightSolarMidnightSolarNoonSunriseSunsetNowNow
The solar day in the fall. 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 the Fall in San Juan

Solar Elevation and Azimuth in the Fall in San JuanSepOctNov12 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 AMSummerWinter0010202030304050600010102030304040506070NowNow
northeastsouthwest
Solar elevation and azimuth in the the fall of 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 the fall of 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 the Fall in San Juan

Moon Rise, Set & Phases in the Fall in San JuanSepOctNov12 AM12 AM4 AM4 AM8 AM8 AM12 PM12 PM4 PM4 PM8 PM8 PM12 AM12 AMSummerWinterAug 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 AMNov 18:48 AMNov 18:48 AMNov 155:29 PMNov 155:29 PMDec 12:22 AMDec 12:22 AMDec 155:02 AMDec 155:02 AMDec 306:28 PMDec 306:28 PM7:24 PM7:24 PM7:02 PM7:02 PM6:52 AM6:52 AM6:35 PM6:35 PM6:16 PM6:16 PM6:36 AM6:36 AM6:11 PM6:11 PM5:28 PM5:28 PM6:19 AM6:19 AM6:23 AM6:23 AM5:53 PM5:53 PM5:33 PM5:33 PM7:14 AM7:14 AM6:03 PM6:03 PM5:08 PM5:08 PM7:05 AM7:05 AM5:46 PM5:46 PMNowNow
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.

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 gradually decreasing during the fall, falling from 100% to 96% over the course of the season.

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 the Fall in San Juan

Humidity Comfort Levels in the Fall in San JuanSepOctNov0%0%10%10%20%20%30%30%40%40%50%50%60%60%70%70%80%80%90%90%100%100%SummerWinterSep 1100%Sep 1100%Nov 3096%Nov 3096%Oct 1100%Oct 1100%Nov 1100%Nov 1100%NowNowmiserablemiserableoppressiveoppressivemuggymuggyhumidhumid
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 essentially constant during the fall, remaining within 1.0 miles per hour of 10.3 miles per hour throughout.

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.

The lowest daily average wind speed during the fall is 9.3 miles per hour on October 10.

Average Wind Speed in the Fall in San Juan

Average Wind Speed in the Fall in San JuanSepOctNov0 mph0 mph2 mph2 mph4 mph4 mph6 mph6 mph8 mph8 mph10 mph10 mph12 mph12 mph14 mph14 mph16 mph16 mphSummerWinterOct 109.3 mphOct 109.3 mphSep 110.8 mphSep 110.8 mphNov 3011.3 mphNov 3011.3 mphNov 19.8 mphNov 19.8 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 the fall is predominantly from the east, with a peak proportion of 89% on September 1.

Wind Direction in the Fall in San Juan

Wind Direction in the Fall in San JuanSepOctNov0%100%20%80%40%60%60%40%80%20%100%0%SummerWinterNowNoweastsouthnorth
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 gradually decreasing during the fall, falling by 2°F, from 84°F to 82°F, over the course of the season.

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

Average Water Temperature in the Fall in San Juan

Average Water Temperature in the Fall in San JuanSepOctNov78°F78°F79°F79°F80°F80°F81°F81°F82°F82°F83°F83°F84°F84°F85°F85°F86°F86°FSummerWinterSep 2684°FSep 2684°FSep 184°FSep 184°FNov 3082°FNov 3082°FNov 183°FNov 183°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 the Fall in San Juan

Time Spent in Various Temperature Bands and the Growing Season in the Fall in San JuanSepOctNov0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%SummerWinter100%Oct 16100%Oct 16NowNowcomfortablewarmhot
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 the fall, increasing by 2,779°F, from 7,222°F to 10,001°F, over the course of the season.

Growing Degree Days in the Fall in San Juan

Growing Degree Days in the Fall in San JuanSepOctNov7,500°F7,500°F8,000°F8,000°F8,500°F8,500°F9,000°F9,000°F9,500°F9,500°F10,000°F10,000°FSummerWinterSep 17,222°FSep 17,222°FNov 3010,001°FNov 3010,001°FOct 18,179°FOct 18,179°FNov 19,144°FNov 19,144°FNowNow
The average growing degree days accumulated over the course of the fall, 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 the fall, falling by 0.5 kWh, from 5.3 kWh to 4.8 kWh, over the course of the season.

The lowest average daily incident shortwave solar energy during the fall is 4.6 kWh on November 2.

Average Daily Incident Shortwave Solar Energy in the Fall in San Juan

Average Daily Incident Shortwave Solar Energy in the Fall in San JuanSepOctNov0 kWh0 kWh1 kWh1 kWh2 kWh2 kWh3 kWh3 kWh4 kWh4 kWh5 kWh5 kWh6 kWh6 kWh7 kWh7 kWh8 kWh8 kWhSummerWinterNov 24.6 kWhNov 24.6 kWhSep 15.3 kWhSep 15.3 kWhNov 304.8 kWhNov 304.8 kWhOct 14.8 kWhOct 14.8 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.

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