This report describes the typical weather at the Juan Santamaría International Airport (San José, Costa Rica) weather station over the course of an average December. It is based on the historical records from 1994 to 2012. Earlier records are either unavailable or unreliable.
San José has a tropical savanna climate with dry winters. The area within 25 mi of this station is covered by forests (68%), croplands (26%), and grasslands (5%).
The month of December is characterized by essentially constant daily high temperatures, with daily highs around 81°F throughout the month, exceeding 84°F or dropping below 77°F only one day in ten.
Over the course of December, the length of the day is essentially constant. The shortest day of the month is December 13 with 11:32 hours of daylight; the longest day is December 3 with 11:35 hours of daylight.
The earliest sunrise is at 5:39am on December 1; the latest sunset is at 5:27pm on December 31; the latest sunrise is at 5:53am on December 31; the earliest sunset is at 5:14pm on December 1.
Daylight saving time (DST) is not observed in 2012.
The median cloud cover ranges from 40% (mostly clear) to 62% (partly cloudy). The trend is for the sky to be clearing rapidly with the median cloud cover decreasing by 22% from the start to the end of the month.
On December 31, the clearest day of the month, the sky is clear, mostly clear, or partly cloudy 49% of the time, and overcast or mostly cloudy 15% of the time.
On December 1, the cloudiest day of the month, the sky is overcast, mostly cloudy, or partly cloudy 52% of the time, and clear or mostly clear 20% of the time.
The probability that precipitation will be observed at this location varies throughout the month. Precipitation is most likely around December 1, occurring in 45% of days. Precipitation is least likely around December 31, occurring in 19% of days.
Throughout December, the most common forms of precipitation are light rain, moderate rain, and drizzle.
Light rain is the most severe precipitation observed during 39% of those days with precipitation. It is most likely around December 3, when it is observed during 15% of all days.
Moderate rain is the most severe precipitation observed during 32% of those days with precipitation. It is most likely around December 1, when it is observed during 16% of all days.
Drizzle is the most severe precipitation observed during 19% of those days with precipitation. It is most likely around December 1, when it is observed during 7% of all days.
Either snow is exceptionally unlikely to fall at this location in December or this station does not reliably report precipitation types.
The relative humidity typically ranges from 51% (mildly humid) to 94% (very humid) over the course of a typical December, rarely dropping below 40% (comfortable) and reaching as high as 100% (very humid).
The air is driest around December 31, at which time the relative humidity drops below 55% (mildly humid) three days out of four; it is most humid around December 1, rising above 89% (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 December, the dew point typically varies from 57°F (comfortable) to 68°F (muggy) and is rarely below 53°F (very comfortable) or above 72°F (very muggy).
Over the course of December typical wind speeds vary from 2 mph to 19 mph (light air to fresh breeze), rarely exceeding 25 mph (strong breeze).
The highest average wind speed of 12 mph (moderate breeze) occurs around December 31, at which time the average daily maximum wind speed is 19 mph (fresh breeze).
The lowest average wind speed of 10 mph (gentle breeze) occurs around December 1, at which time the average daily maximum wind speed is 16 mph (moderate breeze).