This report describes the typical weather at the Luis Muñoz Marín International Airport (San Juan, Puerto Rico) weather station over the course of an average July. It is based on the historical records from 1992 to 2012. Earlier records are either unavailable or unreliable.
San Juan has a tropical rainforest climate with no dry season. The area within 25 mi of this station is covered by oceans and seas (48%), forests (30%), grasslands (12%), marshes (6%), and croplands (3%).
The month of July is characterized by essentially constant daily high temperatures, with daily highs around 88°F throughout the month, exceeding 90°F or dropping below 86°F only one day in ten.
Over the course of July, the length of the day is essentially constant. The shortest day of the month is July 31 with 12:57 hours of daylight; the longest day is July 1 with 13:13 hours of daylight.
The earliest sunrise is at 5:51am on July 1; the latest sunset is at 7:05pm on July 3; the latest sunrise is at 6:02am on July 31; the earliest sunset is at 6:59pm on July 31.
Daylight savings time (DST) is not observed in 2012.
The median cloud cover is 38% (mostly clear) and does not vary substantially over the course of the month.
On July 16, a representative day, the sky is clear or mostly clear 48% of the time, partly cloudy 31% of the time, and mostly cloudy or overcast 16% of the time.
The average probability that some form of precipitation will be observed in a given day is 67%, with little variation over the course of the month.
Throughout July, the most common forms of precipitation are light rain, thunderstorms, heavy rain, and moderate rain.
Light rain is the most severe precipitation observed during 43% of those days with precipitation. It is most likely around July 15, when it is observed during 30% of all days.
Thunderstorms are the most severe precipitation observed during 30% of those days with precipitation. They are most likely around July 31, when it is observed during 21% of all days.
Heavy rain is the most severe precipitation observed during 14% of those days with precipitation. It is most likely around July 31, when it is observed during 10% of all days.
Moderate rain is the most severe precipitation observed during 13% of those days with precipitation. It is most likely around July 19, when it is observed during 9% of all days.
Either snow is exceptionally unlikely to fall at this location in July or this station does not reliably report precipitation types.
The relative humidity typically ranges from 63% (mildly humid) to 90% (very humid) over the course of a typical July, rarely dropping below 56% (mildly humid) and reaching as high as 96% (very humid).
The air is driest around July 1, at which time the relative humidity drops below 67% (mildly humid) three days out of four; it is most humid around July 21, rising above 87% (very humid) three days out of four.
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 July, the dew point typically varies from 72°F (very muggy) to 77°F (oppressive) and is rarely below 70°F (muggy) or above 79°F (oppressive).
Over the course of July typical wind speeds vary from 0 mph to 19 mph (calm to fresh breeze), rarely exceeding 22 mph (fresh breeze).
The highest average wind speed of 10 mph (gentle breeze) occurs around July 1, at which time the average daily maximum wind speed is 19 mph (fresh breeze).
The lowest average wind speed of 9 mph (gentle breeze) occurs around July 31, at which time the average daily maximum wind speed is 18 mph (fresh breeze).