Average Weather in May in Galveston Texas, United States
Daily high temperatures increase by 6°F, from 79°F to 85°F, rarely falling below 74°F or exceeding 88°F.
Daily low temperatures increase by 7°F, from 69°F to 76°F, rarely falling below 63°F or exceeding 79°F.
For reference, on August 5, the hottest day of the year, temperatures in Galveston typically range from 80°F to 90°F, while on January 6, the coldest day of the year, they range from 49°F to 61°F.
Average High and Low Temperature in May
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 May. 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.
The month of May in Galveston experiences gradually decreasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy decreasing from 38% to 33%.
The clearest day of the month is May 31, with clear, mostly clear, or partly cloudy conditions 67% of the time.
For reference, on August 21, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 53%, while on October 26, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 69%.
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 Galveston, the chance of a wet day over the course of May is rapidly increasing, starting the month at 26% and ending it at 33%.
For reference, the year's highest daily chance of a wet day is 42% on September 4, and its lowest chance is 22% on April 1.
Probability of Precipitation in May
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).
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 May in Galveston is increasing, starting the month at 3.7 inches, when it rarely exceeds 7.3 inches or falls below 0.7 inches, and ending the month at 4.5 inches, when it rarely exceeds 9.5 inches or falls below 0.8 inches.
Average Monthly Rainfall in May
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.
Over the course of May in Galveston, the length of the day is increasing. From the start to the end of the month, the length of the day increases by 35 minutes, implying an average daily increase of 1 minute, 10 seconds, and weekly increase of 8 minutes, 11 seconds.
The shortest day of the month is May 1, with 13 hours, 18 minutes of daylight and the longest day is May 31, with 13 hours, 53 minutes of daylight.
Hours of Daylight and Twilight in May
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 latest sunrise of the month in Galveston is 6:37 AM on May 1 and the earliest sunrise is 17 minutes earlier at 6:20 AM on May 31.
The earliest sunset is 7:55 PM on May 1 and the latest sunset is 18 minutes later at 8:13 PM on May 31.
Daylight saving time is observed in Galveston during 2018, but it neither starts nor ends during May, so the entire month is in daylight saving time.
For reference, on June 21, the longest day of the year, the Sun rises at 6:20 AM and sets 14 hours, 1 minute later, at 8:21 PM, while on December 21, the shortest day of the year, it rises at 7:09 AM and sets 10 hours, 16 minutes later, at 5:25 PM.
Sunrise & Sunset with Twilight in May
The solar day over the course of May. 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.
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 Galveston is very rapidly increasing during May, rising from 63% to 91% over the course of the month.
For reference, on July 16, the muggiest day of the year, there are muggy conditions 100% of the time, while on January 23, the least muggy day of the year, there are muggy conditions 4% of the time.
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 Galveston is gradually decreasing during May, decreasing from 11.7 miles per hour to 10.8 miles per hour over the course of the month.
For reference, on December 25, the windiest day of the year, the daily average wind speed is 12.2 miles per hour, while on August 15, the calmest day of the year, the daily average wind speed is 8.4 miles per hour.
Average Wind Speed in May
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 Galveston throughout May is predominantly from the south, with a peak proportion of 67% on May 31.
Wind Direction in May
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).
Galveston 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 Galveston is increasing during May, rising by 7°F, from 73°F to 80°F, over the course of the month.
Average Water Temperature in May
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).
While it does not do so every year, freezing temperatures are seen in Galveston over some winters. The day least likely to be in the growing season is January 16, with a 64% chance.
Time Spent in Various Temperature Bands and the Growing Season in May
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 Galveston are rapidly increasing during May, increasing by 798°F, from 1,432°F to 2,230°F, over the course of the month.
Growing Degree Days in May
The average growing degree days accumulated over the course of May, 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 Galveston is essentially constant during May, remaining within 0.1 kWh of 6.5 kWh throughout.
Average Daily Incident Shortwave Solar Energy in May
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 Galveston are 29.301 deg latitude, -94.798 deg longitude, and 3 ft elevation.
The topography within 2 miles of Galveston is essentially flat, with a maximum elevation change of 20 feet and an average elevation above sea level of 5 feet. Within 10 miles is also essentially flat (26 feet). Within 50 miles is essentially flat (112 feet).
The area within 2 miles of Galveston is covered by artificial surfaces (54%), water (25%), and bare soil (11%), within 10 miles by water (80%), and within 50 miles by water (57%) and cropland (19%).
This report illustrates the typical weather in Galveston year round, 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 Galveston.
The estimated value at Galveston is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Galveston and a given station.
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.
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.