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Average Weather at South Marsh Island Louisiana, United States

At South Marsh Island, the summers are hot, oppressive, and mostly cloudy; the winters are comfortable, windy, and partly cloudy; and it is wet year round. Over the course of the year, the temperature typically varies from 59°F to 90°F and is rarely below 48°F or above 94°F.

Climate Summary

comfortablewarmhotwarmJanFebMarAprMayJunJulAugSepOctNovDec63%63%38%38%clearovercastprecipitation: 6.0 inprecipitation: 6.0 in3.4 in3.4 inmuggy: 99%muggy: 99%15%15%drydrybeach/pool score: 7.1beach/pool score: 7.12.12.1
Click on each chart for more information.

Based on the beach/pool score, the best times of year to visit South Marsh Island for hot-weather activities are from late April to early June and from late September to late October.

Temperature

The hot season lasts for 3.4 months, from June 4 to September 17, with an average daily high temperature above 86°F. The hottest day of the year is July 27, with an average high of 90°F and low of 83°F.

The cool season lasts for 3.2 months, from December 8 to March 15, with an average daily high temperature below 73°F. The coldest day of the year is January 23, with an average low of 59°F and high of 68°F.

Average High and Low Temperature

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 entire year of hourly average temperatures. The horizontal axis is the day of the year, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.

Average Hourly Temperature

Average Hourly Temperature at South Marsh IslandJanFebMarAprMayJunJulAugSepOctNovDec12 AM4 AM8 AM12 PM4 PM8 PM12 AMcoolcomfortablecomfortablewarmwarmhotcool
The average hourly temperature, color coded into bands: 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 shaded overlays indicate night and civil twilight.

Hong Kong, Hong Kong SAR China (8,541 miles away) is the far-away foreign place with temperatures most similar to South Marsh Island (view comparison).

Clouds

At South Marsh Island, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.

The clearer part of the year at South Marsh Island begins around January 30 and lasts for 4.8 months, ending around June 22. On May 19, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 63% of the time, and overcast or mostly cloudy 37% of the time.

The cloudier part of the year begins around June 22 and lasts for 7.2 months, ending around January 30. On July 31, the cloudiest day of the year, the sky is overcast or mostly cloudy 62% of the time, and clear, mostly clear, or partly cloudy 38% of the time.

Cloud Cover Categories

Cloud Cover Categories at South Marsh IslandclearercloudierJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%May 1963%May 1963%Jul 3138%Jul 3138%Jan 3051%Jan 3051%Jun 2251%Jun 2251%clearmostly clearpartly cloudymostly cloudyovercast
The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds: clear < 20% < mostly clear < 40% < partly cloudy < 60% < mostly cloudy < 80% < overcast.

Precipitation

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days at South Marsh Island varies significantly throughout the year.

The wetter season lasts 3.2 months, from June 8 to September 15, with a greater than 43% chance of a given day being a wet day. The chance of a wet day peaks at 59% on July 30.

The drier season lasts 8.8 months, from September 15 to June 8. The smallest chance of a wet day is 26% on March 13.

Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 59% on July 30.

Daily Chance of Precipitation

Daily Chance of Precipitation at South Marsh IslandwetdrydryJanFebMarAprMayJunJulAugSepOctNovDec0%10%20%30%40%50%60%70%80%90%100%Jul 3059%Jul 3059%Mar 1326%Mar 1326%Jan 133%Jan 133%Jun 843%Jun 843%Sep 1543%Sep 1543%rain
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 months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. South Marsh Island experiences significant seasonal variation in monthly rainfall.

Rain falls throughout the year at South Marsh Island. The most rain falls during the 31 days centered around August 31, with an average total accumulation of 6.0 inches.

The least rain falls around April 30, with an average total accumulation of 3.4 inches.

Average Monthly Rainfall

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 liquid-equivalent snowfall.

Sun

The length of the day at South Marsh Island varies over the course of the year. In 2017, the shortest day is December 21, with 10 hours, 21 minutes of daylight; the longest day is June 21, with 13 hours, 57 minutes of daylight.

Hours of Daylight and Twilight

Hours of Daylight and Twilight at South Marsh IslandJanFebMarAprMayJunJulAugSepOctNovDec0 hr24 hr4 hr20 hr8 hr16 hr12 hr12 hr16 hr8 hr20 hr4 hr24 hr0 hr12 hr, 6 minMar 2012 hr, 6 minMar 2013 hr, 57 minJun 2113 hr, 57 minJun 2112 hr, 8 minSep 2212 hr, 8 minSep 2210 hr, 21 minDec 2110 hr, 21 minDec 21nightnightday
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 is at 7:10 AM on June 10, and the latest sunrise is 1 hour, 12 minutes later at 8:21 AM on November 4. The earliest sunset is at 6:11 PM on December 1, and the latest sunset is 2 hours, 58 minutes later at 9:09 PM on June 30.

Daylight saving time (DST) is observed at South Marsh Island during 2017, starting in the spring on March 12, lasting 7.8 months, and ending in the fall on November 5.

Sunrise & Sunset with Twilight and Daylight Saving Time

Sunrise & Sunset with Twilight and Daylight Saving Time at South Marsh IslandJanFebMarAprMayJunJulAugSepOctNovDec2 AM4 AM6 AM8 AM10 AM12 PM2 PM4 PM6 PM8 PM10 PM12 AM2 AMJun 107:10 AMJun 107:10 AM9:09 PMJun 309:09 PMJun 30Dec 16:11 PMDec 16:11 PM8:21 AMNov 48:21 AMNov 4Mar 12DSTMar 12DSTDSTNov 5DSTNov 5daynightnightnightnightSolarMidnightSolarMidnightSolarNoonSunriseSunset
The solar day over the course of the year 2017. 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 transitions to and from daylight saving time are indicated by the 'DST' labels.

Humidity

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.

South Marsh Island experiences extreme seasonal variation in the perceived humidity.

The muggier period of the year lasts for 8.0 months, from March 16 to November 15, during which time the comfort level is muggy, oppressive, or miserable at least 36% of the time. The muggiest day of the year is July 21, with muggy conditions 99% of the time.

The least muggy day of the year is January 29, with muggy conditions 15% of the time.

Humidity Comfort Levels

Humidity Comfort Levels at South Marsh IslandmuggyJanFebMarAprMayJunJulAugSepOctNovDec0%10%20%30%40%50%60%70%80%90%100%Jan 2915%Jan 2915%99%Jul 2199%Jul 21Mar 1636%Mar 1636%Nov 1536%Nov 1536%miserablemiserableoppressiveoppressivedrydrymuggymuggyhumidhumidcomfortablecomfortable
The percentage of time spent at various humidity comfort levels, categorized by dew point: dry < 55°F < comfortable < 60°F < humid < 65°F < muggy < 70°F < oppressive < 75°F < miserable.

Wind

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 at South Marsh Island experiences significant seasonal variation over the course of the year.

The windier part of the year lasts for 7.9 months, from September 18 to May 13, with average wind speeds of more than 11.8 miles per hour. The windiest day of the year is December 27, with an average hourly wind speed of 15.5 miles per hour.

The calmer time of year lasts for 4.1 months, from May 13 to September 18. The calmest day of the year is August 8, with an average hourly wind speed of 8.1 miles per hour.

Average Wind Speed

Average Wind Speed at South Marsh IslandwindywindyJanFebMarAprMayJunJulAugSepOctNovDec0 mph2 mph4 mph6 mph8 mph10 mph12 mph14 mph16 mph18 mph20 mph22 mphDec 2715.5 mphDec 2715.5 mphAug 88.1 mphAug 88.1 mphSep 1811.8 mphSep 1811.8 mphMay 1311.8 mphMay 1311.8 mph
The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.

The predominant average hourly wind direction at South Marsh Island varies throughout the year.

The wind is most often from the east for 1.1 months, from February 21 to March 23 and for 3.3 months, from August 15 to November 24, with a peak percentage of 53% on September 23. The wind is most often from the south for 4.7 months, from March 23 to August 15, with a peak percentage of 51% on June 21. The wind is most often from the north for 2.9 months, from November 24 to February 21, with a peak percentage of 36% on January 1.

Wind Direction

Wind Direction at South Marsh IslandNESENJanFebMarAprMayJunJulAugSepOctNovDec0%100%20%80%40%60%60%40%80%20%100%0%southeastnorthwest
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions (north, east, south, and west), excluding hours in which the mean wind speed is less than 1 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

Water Temperature

South Marsh Island 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 water temperature experiences some seasonal variation over the course of the year.

The time of year with warmer water lasts for 3.7 months, from June 12 to October 2, with an average temperature above 82°F. The day of the year with the warmest water is August 5, with an average temperature of 86°F.

The time of year with cooler water lasts for 3.6 months, from December 20 to April 9, with an average temperature below 71°F. The day of the year with the coolest water is February 8, with an average temperature of 67°F.

Average Water Temperature

The daily average water temperature (purple line), with 25th to 75th and 10th to 90th percentile bands.

Best Time of Year to Visit

To characterize how pleasant the weather is at South Marsh Island throughout the year, we compute two travel scores.

The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best times of year to visit South Marsh Island for general outdoor tourist activities are from late February to early May and from late October to early December, with a peak score in the first week of April.

Tourism Score

Tourism Score at South Marsh Islandbest timebest timeJanFebMarAprMayJunJulAugSepOctNovDec02468107.17.12.22.26.96.95.55.5 precipitationprecipitationcloudscloudstemperaturetemperaturetourism score
The tourism score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).

The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best times of year to visit South Marsh Island for hot-weather activities are from late April to early June and from late September to late October, with a peak score in the second week of May.

Beach/Pool Score

Beach/Pool Score at South Marsh Islandbest timeJanFebMarAprMayJunJulAugSepOctNovDec02468107.17.12.12.16.86.83.83.8 precipitationprecipitationcloudscloudstemperaturetemperaturebeach/pool score
The beach/pool score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).

Methodology

For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.

Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.

Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.

Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.

Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.

Growing Season

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 at South Marsh Island 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

Time Spent in Various Temperature Bands and the Growing Season at South Marsh IslandJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%100%Jan 15100%Jan 1599%Dec 2799%Dec 27Jun 27100%Jun 27100%coldcoolcomfortablewarmhot
The percentage of time spent in various temperature bands: 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 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.

Growing Degree Days

Growing Degree Days at South Marsh IslandJanFebMarAprMayJunJulAugSepOctNovDec0°F1,000°F2,000°F3,000°F4,000°F5,000°F6,000°F7,000°F8,000°F9,000°FJan 890°FJan 890°FMar 4900°FMar 4900°FApr 181,800°FApr 181,800°FDec 319,245°FDec 319,245°F
The average growing degree days accumulated over the course of the year, with 25th to 75th and 10th to 90th percentile bands.

Solar Energy

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 experiences significant seasonal variation over the course of the year.

The brighter period of the year lasts for 2.5 months, from April 1 to June 18, with an average daily incident shortwave energy per square meter above 5.9 kWh. The brightest day of the year is May 19, with an average of 6.6 kWh.

The darker period of the year lasts for 2.5 months, from November 16 to February 2, with an average daily incident shortwave energy per square meter below 3.8 kWh. The darkest day of the year is December 23, with an average of 3.1 kWh.

Average Daily Incident Shortwave Solar Energy

Average Daily Incident Shortwave Solar Energy at South Marsh IslandbrightdarkdarkJanFebMarAprMayJunJulAugSepOctNovDec0 kWh1 kWh2 kWh3 kWh4 kWh5 kWh6 kWh7 kWh8 kWh9 kWhMay 196.6 kWhMay 196.6 kWhDec 233.1 kWhDec 233.1 kWhApr 15.9 kWhApr 15.9 kWhFeb 23.8 kWhFeb 23.8 kWh
The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.

Data Sources

This report illustrates the typical weather at South Marsh Island, 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

South Marsh Island has a weather station that reported reliably enough during the analysis period that we have included it in our network. When available, historical temperature and dew point measurements are taken directly from this weather station. These records are obtained from NOAA's Integrated Surface Hourly data set, falling back on ICAO METAR records as required.

In the case of missing or erroneous measurements from this station, we fall back on records from nearby stations, adjusted according to typical seasonal and diurnal intra-station differences. For a given day of the year and hour of the day, the fallback station is selected to minimize the prediction error over the years for which there are measurements for both stations.

The stations on which we may fall back are West Cameron, Green Canyon 184, Ship Shoal Platform, East Addition B323, Salt Point, High Island A572c, Abbeville Chris Crusta Memorial Airport, and Harry P Williams Memorial Airport.

Other Data

All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Tables of the Sun, Moon and Planets , 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 aiports and weather stations are provided by AskGeo.com .

Maps are © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.

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.