Average high temperature and rainfall for San Juan in September. © Scott S. Bateman

San Juan weather in September has plenty of warm temperatures, but it also has some of the highest rainfall of the year.

The San Juan cruise port attracts many eastern Caribbean cruise ships. It’s also a common embarkation port for southern Caribbean cruises. It offers some of the same weather as other Caribbean destinations. In September, that usually means higher than normal amounts of rain thanks to the Caribbean hurricane season.

San Juan Temperatures in September

San Juan temperatures in September have an average high of 89 degrees Fahrenheit or 31 Celsius, according to the U.S. National Weather Service. Low temperatures average 77 degrees Fahrenheit or 25 Celsius.

September temperatures are about the same as June, July, August and October. They are the highest of the year. In contrast, daytime temperatures reach a low point of 83 degrees Fahrenheit or 28 Celsius in January.

Water temperatures in September stay about midway between the daytime highs and nighttime lows. They feel warm to balmy throughout most of the day. They are warmest in the afternoons and coolest in the mornings.

Rainy Season in September

September rainfall for San Juan historically is the highest of the year along with August, October and November. They average about five to six inches of rain each month, according to the U.S. National Weather Service. This total is consistent with many other Caribbean destinations during hurricane season, which goes from June through November.

Rain falls more often in September than earlier in the year. The total days with rain in September averages 13. This compares to eight to nine days from February through April during the dry season.

San Juan weather in September is one of the riskiest months to visit because of higher than average rainfall as well as a higher risk of tropical storms and hurricanes. Travelers who want warm weather in San Juan during the summer have better chances by going in June rather than September. July usually has less rain than August but more than June.

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