From Merra report

In Juba, the wet season is hot and oppressive, the dry season is sweltering, and it is mostly cloudy year round. Over the course of the year, the temperature typically varies from 71°F to 102°F and is rarely below 68°F or above 107°F.

The hot season lasts for 2.6 months, from January 16 to April 5, with an average daily high temperature above 99°F. The hottest day of the year is March 2, with an average high of 102°F and low of 78°F.

The cool season lasts for 3.4 months, from June 10 to September 21, with an average daily high temperature below 89°F. The coldest day of the year is August 5, with an average low of 71°F and high of 86°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 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.

In Juba, the average percentage of the sky covered by clouds experiences significant seasonal variation. The clearer part of the year in Juba begins around August 2 and lasts for 2.2 months, ending around October 8. On September 2, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 52% of the time, and overcast or mostly cloudy 48% of the time.

The cloudier part of the year begins around October 8 and lasts for 9.8 months, ending around August 2. On April 19, the cloudiest day of the year, the sky is overcast or mostly cloudy 81% of the time, and clear, mostly clear, or partly cloudy 19% of the time.

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 in Juba varies very significantly throughout the year.

The wetter season lasts 6.5 months, from April 20 to November 5, with a greater than 36% chance of a given day being a wet day. The chance of a wet day peaks at 69% on August 12.

The drier season lasts 5.5 months, from November 5 to April 20. The smallest chance of a wet day is 2% on January 21.

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 69% on August 12.

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 on each day of the year. Juba experiences extreme seasonal variation in monthly rainfall.

The rainy period of the year lasts for 9.2 months, from March 2 to December 9, with a sliding 31-day rainfall of at least 0.5 inches. The most rain falls during the 31 days centered on August 10, with an average total accumulation of 5.6 inches.

The rainless period of the year lasts for 2.8 months, from December 9 to March 2. The least rain falls around January 18, with an average total accumulation of 0.1 inches.

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.

The length of the day in Juba does not vary substantially over the course of the year, staying within 24 minutes of 12 hours throughout. In 2018, the shortest day is December 22, with 11 hours, 51 minutes of daylight; the longest day is June 21, with 12 hours, 24 minutes of daylight.

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 6:38 AM on October 25, and the latest sunrise is 31 minutes later at 7:09 AM on February 4. The earliest sunset is at 6:35 PM on November 10, and the latest sunset is 36 minutes later at 7:10 PM on July 17.

The solar day over the course of the year 2018. 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.

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.

Juba experiences extreme seasonal variation in the perceived humidity.

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 Juba experiences significant seasonal variation over the course of the year.

The calmer time of year lasts for 6.6 months, from April 25 to November 13. The calmest day of the year is July 19, with an average hourly wind speed of 4.2 miles per hour.

The predominant average hourly wind direction in Juba varies throughout the year.

To characterize how pleasant the weather is in Juba 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 time of year to visit Juba for general outdoor tourist activities is from late June to late September, with a peak score in the last week of August.

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.

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 Juba 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.

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 daily incident shortwave solar energy experiences some seasonal variation over the course of the year.

This report illustrates the typical weather in Juba, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.

Juba is further than 200 kilometers from the nearest reliable weather station, so the weather-related data on this page were taken entirely from NASA’s MERRA-2 satellite-era reanalysis.

 

 

 

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