San Juan Monthly Rainfall & Precipitation

This page shows both the average monthly rainfall and the number of rainy days in San Juan, North Puerto Rico, Puerto Rico. Long-term data from 1990 to 2020 was used to calculate these averages. Now, let's break down all the details for a clearer picture.

San Juan experiences significant rainfall throughout the year, averaging 1192 mm (47 in) of precipitation annually.

Monthly Precipitation Levels

The average number of days each month with precipitation (> 0.2 mm (0.01 in))

San Juan can be quite wet during September, receiving approximately 159 mm (6.3 in) of precipitation over 18 rainy days.

In contrast February, experiences much drier conditions, with 47 mm (1.9 in) of rainfall, spread across 15 rainy days.

September, the wettest month, has a maximum daytime temperature of 31°C (88°F). The city receives 236 hours of sunshine in this period. During the driest month February you can expect a temperature of 28°C (82°F). For more detailed insights into the city's temperatures, visit our San Juan Temperature page.

San Juan's average annual precipitation is 1192 mm (47 in). Let's compare this to some popular worldwide tourist destinations:

In Lisbon, Portugal, the average annual precipitation is 774 mm (30 in), characterized by wet winters and dry summers typical of the Mediterranean climate.

In Seoul, South Korea, the average annual precipitation is 1237 mm (49 in), with most rain falling during the summer monsoon season.

Melbourne, Australia, has 690 mm (27 in) of rainfall annually, spread fairly evenly throughout the year.

Ho Chi Minh City, Vietnam, receives 1955 mm (77 in) of annual rainfall, with a pronounced wet season from May to November, typical of its tropical monsoon climate.

Precipitation amounts are measured using specific gauges installed at weather stations, collecting both rain and snow and any other type of precipitation. Rainfall is measured directly in millimeters, while that from snow and ice is obtained by melting it. Automated systems often incorporate heaters to make this easier.

Information from these stations is transmitted via Wi-Fi, satellite, GPS, or telephone connections to central monitoring networks. This information is immediately updated and integrated into weather models and forecasts.

Climate change is affecting precipitation patterns worldwide, including San Juan:

• Changing Rainfall Patterns: Global warming causes drastic changes in the patterns of rainfall. Some areas have been experiencing increased frequency and intensity of rainfall, while other areas experience longer dry spells or even droughts.
• Local Impacts: Many regions are experiencing heavier rainfall in the winter months and drier, hotter summers. This affects agriculture, water resources, and ecosystems.

• "Ginger" was the longest-lasting Atlantic tropical storm, which spun around the open ocean for 28 days in 1971.
• The world's largest snowflake was recorded in the Guinness Book of Records, at 38 cm (15 inches) wide and 20 cm (7.9 inches) thick. The snowflake fell at Fort Keogh, Montana, USA, on 28 January 1887.
• The greatest snowfall recorded was on Mt. Rainier, Washington State, USA, over 31.5 meters (103 feet) fell during the winter of 1972.

For more detailed information about San Juan's weather, including sunshine hours, humidity levels, and temperature data, visit our San Juan Climate page.