This report describes the typical weather at the Cyril E. King Airport (St. Thomas, US Virgin Islands) weather station over the course of an average December. It is based on the historical records from 1974 to 2012. Earlier records are either unavailable or unreliable.
St. Thomas has a tropical savanna climate with dry winters. The area within 25 mi of this station is covered by oceans and seas (99%).
The month of December is characterized by essentially constant daily high temperatures, with daily highs around 85°F throughout the month, exceeding 88°F or dropping below 81°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 19 with 11:01 hours of daylight; the longest day is December 1 with 11:07 hours of daylight.
The earliest sunrise is at 6:36am on December 1; the latest sunset is at 5:55pm on December 31; the latest sunrise is at 6:51am on December 30; the earliest sunset is at 5:43pm on December 1.
Daylight savings time (DST) is not observed in 2012.
The median cloud cover is 24% (mostly clear) and does not vary substantially over the course of the month.
On December 16, a representative day, the sky is clear or mostly clear 52% of the time, partly cloudy 6% of the time, and mostly cloudy or overcast 18% 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 36% of days. Precipitation is least likely around December 31, occurring in 32% of days.
Throughout December, the most common forms of precipitation are light rain, moderate rain, and heavy rain.
Light rain is the most severe precipitation observed during 50% of those days with precipitation. It is most likely around December 21, when it is observed during 17% of all days.
Moderate rain is the most severe precipitation observed during 29% of those days with precipitation. It is most likely around December 2, when it is observed during 10% of all days.
Heavy rain 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 8% 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 59% (mildly humid) to 85% (very humid) over the course of a typical December, rarely dropping below 50% (mildly humid), or exceeding 95% (very humid).
The air is driest around December 9, at which time the relative humidity drops below 64% (mildly humid) three days out of four; it is most humid around December 18, rising above 80% (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 66°F (muggy) to 72°F (very muggy) and is rarely below 61°F (comfortable) or above 76°F (very muggy).
Over the course of December typical wind speeds vary from 6 mph to 17 mph (light breeze to moderate breeze), rarely exceeding 22 mph (fresh breeze).
The highest average wind speed of 11 mph (gentle breeze) occurs around December 30, at which time the average daily maximum wind speed is 17 mph (moderate breeze).
The lowest average wind speed of 10 mph (gentle breeze) occurs around December 20, at which time the average daily maximum wind speed is 17 mph (moderate breeze).