September Weather in Charlotte Amalie U.S. Virgin Islands
Daily high temperatures are around 88°F, rarely falling below 85°F or exceeding 92°F.
Daily low temperatures are around 79°F, rarely falling below 76°F or exceeding 82°F.
For reference, on August 6, the hottest day of the year, temperatures in Charlotte Amalie typically range from 79°F to 89°F, while on January 21, the coldest day of the year, they range from 73°F to 83°F.
Average High and Low Temperature in September in Charlotte Amalie
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 Charlotte Amalie
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
Malindi, Kenya (7,283 miles away); Vũng Tàu, Vietnam (10,393 miles); and Pandan, Philippines (10,126 miles) are the far-away foreign places with temperatures most similar to Charlotte Amalie (view comparison).
The month of September in Charlotte Amalie experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 66% throughout the month. The highest chance of overcast or mostly cloudy conditions is 68% on September 26.
The clearest day of the month is September 1, with clear, mostly clear, or partly cloudy conditions 36% of the time.
For reference, on May 30, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 72%, while on January 11, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 83%.
Cloud Cover Categories in September in Charlotte Amalie
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Charlotte Amalie, the chance of a wet day over the course of September is essentially constant, remaining around 37% throughout.
For reference, the year's highest daily chance of a wet day is 38% on September 20, and its lowest chance is 11% on March 8.
Probability of Precipitation in September in Charlotte Amalie
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 Charlotte Amalie is gradually increasing, starting the month at 3.0 inches, when it rarely exceeds 5.9 inches or falls below 0.9 inches, and ending the month at 3.5 inches, when it rarely exceeds 6.6 inches or falls below 0.8 inches.
The highest average 31-day accumulation is 3.6 inches on September 19.
Average Monthly Rainfall in September in Charlotte Amalie
Over the course of September in Charlotte Amalie, 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, 1 second, and weekly decrease of 7 minutes, 9 seconds.
The shortest day of the month is September 30, with 11 hours, 59 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 Charlotte Amalie
The earliest sunrise of the month in Charlotte Amalie is 6:05 AM on September 1 and the latest sunrise is 5 minutes later at 6:10 AM on September 30.
The latest sunset is 6:33 PM on September 1 and the earliest sunset is 25 minutes earlier at 6:08 PM on September 30.
Daylight saving time is not observed in Charlotte Amalie during 2021.
For reference, on June 21, the longest day of the year, the Sun rises at 5:44 AM and sets 13 hours, 14 minutes later, at 6:58 PM, while on December 21, the shortest day of the year, it rises at 6:47 AM and sets 11 hours, 2 minutes later, at 5:48 PM.
Sunrise & Sunset with Twilight in September in Charlotte Amalie
The figure below presents a compact representation of key lunar data for September 2021. 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 Charlotte Amalie
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 Charlotte Amalie is essentially constant during September, remaining around 99% throughout.
For reference, on August 1, the muggiest day of the year, there are muggy conditions 100% of the time, while on February 27, the least muggy day of the year, there are muggy conditions 71% of the time.
Humidity Comfort Levels in September in Charlotte Amalie
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
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 Charlotte Amalie is decreasing during September, decreasing from 13.8 miles per hour to 12.1 miles per hour over the course of the month.
For reference, on July 14, the windiest day of the year, the daily average wind speed is 16.0 miles per hour, while on October 10, the calmest day of the year, the daily average wind speed is 11.8 miles per hour.
Average Wind Speed in September in Charlotte Amalie
The hourly average wind direction in Charlotte Amalie throughout September is predominantly from the east, with a peak proportion of 90% on September 1.
Wind Direction in September in Charlotte Amalie
Charlotte Amalie 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 Charlotte Amalie is essentially constant during September, remaining around 84°F throughout.
The highest average surface water temperature during September is 84°F on September 25.
Average Water Temperature in September in Charlotte Amalie
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 Charlotte Amalie 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 Charlotte Amalie
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
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 Charlotte Amalie are very rapidly increasing during September, increasing by 947°F, from 7,369°F to 8,316°F, over the course of the month.
Growing Degree Days in September in Charlotte Amalie
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 Charlotte Amalie is gradually decreasing during September, falling by 0.6 kWh, from 5.4 kWh to 4.7 kWh, over the course of the month.
Average Daily Incident Shortwave Solar Energy in September in Charlotte Amalie
For the purposes of this report, the geographical coordinates of Charlotte Amalie are 18.342 deg latitude, -64.931 deg longitude, and 33 ft elevation.
The topography within 2 miles of Charlotte Amalie contains very significant variations in elevation, with a maximum elevation change of 1,558 feet and an average elevation above sea level of 296 feet. Within 10 miles also contains very significant variations in elevation (1,604 feet). Within 50 miles also contains very significant variations in elevation (1,781 feet).
The area within 2 miles of Charlotte Amalie is covered by grassland (38%), water (23%), and trees (23%), within 10 miles by water (91%), and within 50 miles by water (97%).
This report illustrates the typical weather in Charlotte Amalie, 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 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Charlotte Amalie.
For each station, the records are corrected for the elevation difference between that station and Charlotte Amalie 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 Charlotte Amalie is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Charlotte Amalie 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 Charlotte Amalie 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.
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 © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.
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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