Average Weather In May For Johannesburg, South Africa

Location

This report describes the typical weather at the OR Tambo International Airport (Johannesburg, South Africa) weather station over the course of an average May. It is based on the historical records from 1994 to 2012. Earlier records are either unavailable or unreliable.

Johannesburg has a mild temperate climate with dry winters and warm summers. The area within 25 mi of this station is covered by grasslands (90%) and built-up areas (10%).

Temperature

The month of May is characterized by falling daily high temperatures, with daily highs decreasing from 68°F to 63°F over the course of the month, exceeding 75°F or dropping below 56°F only one day in ten.

Daily High and Low Temperature in May

The daily average low (blue) and high (red) temperature with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).
Daily low temperatures range from 42°F to 49°F, falling below 34°F or exceeding 54°F only one day in ten.

Fraction of Time Spent in Various Temperature Bands in May

The average fraction of time spent in various temperature bands: frigid (below 15°F), freezing (15°F to 32°F), cold (32°F to 50°F), cool (50°F to 65°F), comfortable (65°F to 75°F), warm (75°F to 85°F), hot (85°F to 100°F) and sweltering (above 100°F).

Sun

Over the course of May, the length of the day is essentially constant. The shortest day of the month is May 30 with 10:37 hours of daylight; the longest day is May 1 with 11:06 hours of daylight.

Daily Hours of Daylight and Twilight in May

The number of hours during which the Sun is visible (black line), with various degrees of daylight, twilight, and night, indicated by the color bands. From bottom (most yellow) to top (most gray): full daylight, solar twilight (Sun is visible but less than 6° from the horizon), civil twilight (Sun is not visible but is less than 6° below the horizon), nautical twilight (Sun is between 6° and 12° below the horizon), astronomical twilight (Sun is between 12° and 18° below the horizon), and full night.

The earliest sunrise is at 6:31am on May 1; the latest sunset is at 5:37pm on May 1; the latest sunrise is at 6:46am on May 31; the earliest sunset is at 5:23pm on May 30.

Daylight savings time (DST) is not observed in 2012.

Daily Sunrise & Sunset with Twilight in May

The solar day over the course of the year 2012 . From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (solar, civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray.

Clouds

The median cloud cover ranges from 9% (clear) to 22% (mostly clear). The trend is for the sky to be clearing with the median cloud cover decreasing by 13% from the start to the end of the month.

Median Cloud Cover in May

The median daily cloud cover (black line) with percentile bands (inner band from 40th to 60th percentile, outer band from 25th to 75th percentile).

On May 31, the clearest day of the month, the sky is clear, mostly clear, or partly cloudy 60% of the time, and overcast or mostly cloudy 8% of the time.

On May 1, the cloudiest day of the month, the sky is overcast, mostly cloudy, or partly cloudy 23% of the time, and clear or mostly clear 47% of the time.

Cloud Cover Types in May

The fraction of time spent in each of the five sky cover categories. From top (most blue) to bottom (most gray), the categories are clear, mostly clear, partly cloudy, mostly cloudy, and overcast. Pink indicates missing data. Outside of the United States clear skies are often reported ambiguously, leading them to be lumped in with the missing data.

Precipitation

The probability that precipitation will be observed at this location varies throughout the month. Precipitation is most likely around May 1, occurring in 22% of days. Precipitation is least likely around May 31, occurring in 10% of days.

Probability of Precipitation at Some Point in the Day in May

The fraction of days in which various types of precipitation are observed. If more than one type of precipitation is reported in a given day, the more severe precipitation is counted. For example, if light rain is observed in the same day as a thunderstorm, that day counts towards the thunderstorm totals. The order of severity is from the top down in this graph, with the most severe at the bottom.

Throughout May, the most common forms of precipitation are thunderstorms, light rain, and moderate rain.

Thunderstorms are the most severe precipitation observed during 43% of those days with precipitation. They are most likely around May 1, when it is observed during 10% of all days.

Light rain is the most severe precipitation observed during 30% of those days with precipitation. It is most likely around May 1, when it is observed during 6% of all days.

Moderate rain is the most severe precipitation observed during 24% of those days with precipitation. It is most likely around May 1, when it is observed during 5% of all days.

Types of Precipitation Throughout May

Relative frequency of various types of precipitation over the course of a typical May.

Snow

Either snow is exceptionally unlikely to fall at this location in May or this station does not reliably report precipitation types.

Humidity

The relative humidity typically ranges from 30% (comfortable) to 88% (very humid) over the course of a typical May, rarely dropping below 14% (very dry) and reaching as high as 100% (very humid).

The air is driest around May 31, at which time the relative humidity drops below 38% (comfortable) three days out of four; it is most humid around May 1, rising above 81% (humid) three days out of four.

Relative Humidity in May

The average daily high (blue) and low (brown) relative humidity with percentile bands (inner bands from 25th to 75th percentile, outer bands from 10th to 90th percentile).

Dew Point

Dew point is often a better measure of how comfortable a person will find the weather than relative humidity because it more directly relates to whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid.

Over the course of a typical May, the dew point typically varies from 26°F (dry) to 48°F (dry) and is rarely below 12°F (dry) or above 55°F (very comfortable).

Dew Point in May

The daily average low (blue) and high (red) dew point with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).

Wind

Over the course of May typical wind speeds vary from 2 mph to 12 mph (light air to moderate breeze), rarely exceeding 19 mph (fresh breeze).

The highest average wind speed of 8 mph (gentle breeze) occurs around May 31, at which time the average daily maximum wind speed is 12 mph (moderate breeze).

The lowest average wind speed of 7 mph (light breeze) occurs around May 17, at which time the average daily maximum wind speed is 11 mph (gentle breeze).

Wind Speed in May

The average daily minimum (red), maximum (green), and average (black) wind speed with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).
The wind is most often out of the north (23% of the time), north west (18% of the time), and east (11% of the time). The wind is least often out of the south east (5% of the time).

Wind Directions in May

The fraction of time spent with the wind blowing from the various directions over the entire year. Values do not sum to 100% because the wind direction is undefined when the wind speed is zero.

Fraction of Time Spent with Various Wind Directions in May

The fraction of time spent with the wind blowing from the various directions on a daily basis. Stacked values do not always sum to 100% because the wind direction is undefined when the wind speed is zero.