December 2009 Climate Report

December 2009 Climate Report for Puerto Rico and the U.S. Virgin Islands

December 2009 Highlights:

Temperatures across Puerto Rico ranged from 50ºF in Adjuntas on the 21^st of December to 94ºF on Magueyes Island, on the 19^th of the month. Temperatures across the U.S. Virgin Islands ranged from 62ºF, December 30^th, at Beth Upper New Works on Saint Croix, to 89ºF, observed at Charlotte Amalie on Saint Thomas on the 4^th of the month. Other notable temperatures for December 2009 are listed below:

Other Notable December 2009 High Temps:

93ºF in Rincon on December 19^th

93ºF in Ponce on December 3^rd

92ºF in Lajas on December 17^th

91ºF in Aguirre Central on December 15^th

91ºF in Bourinquen on December 5^th

90ºF at Coloso and Guayama

Other Notable December 2009 Low Temps:

58ºF in Lajas on December 18^th

59ºF in Ponce on December 18^th

59ºF in Toro Negro on December 22^nd

61ºF in Aibonito, Gurabo, Cerro Maravilla and Coloso

^{*If multiple occurrences, all dates above reflect the most recent occurrence of the month.}

The highest 24-hour precipitation total for the month of December was 9.00”, which fell in Aibonito on the 25^th of the month. The highest weekly rainfall also occurred in Aibonito, where 9.19” of rainfall accumulated the week ending December 25^th. While just over two inches of rain fell on Saint Croix during the month of December, this was over an inch below normal for the month, and the 12^th consecutive month that the Christiansted Airport on Saint Croix received below normal. Not surprisingly, 2009 ranked as the second driest calendar year on record for Saint Croix, second only to 2002.

Figure 1A – Island wide precipitation for January-December2009

Figure 1B – Graphical Display of December 2009 precipitation across Puerto Rico and the U.S. Virgin Islands derived from a combination of rain gage and radar data.

Monthly Weather Summary:

December 2009 began with an upper level ridge across the Western Caribbean that helped to limit shower activity across the local islands for much of the month. These fair weather conditions prevailed across the forecast area until Christmas Eve when a large band of moisture stretching from South America northward across Puerto Rico brought cloudy skies and scattered to numerous showers across the region. Several flash flood warnings were issued across the eastern portion of the island due to the heavy rain associated to this band of moisture. The remnants of an old frontal boundary were the last weather feature that affected the forecast area in 2009, with the aforementioned mid to upper level ridge of high pressure limiting the development of significant precipitation across the island for the majority of the month.

On average, the Luis Muñoz International Airport in San Juan receives 4.57" of rain during the month of December, making December the fifth wettest month on the island, however, this was not the case in 2009. December was considerably above normal, in terms of temperature, and well below normal, in terms of precipitation. December 2009 ended as the 2^nd warmest December on record, the 3^rd driest December on record, and the driest month observed in 2009. A total of only 1.83" fell over the course of the month, which was 2.54” below the 30-year average.

December 2009 Statistics:

Average December Temperatures/Precipitation (NCDC 1971-2000 averages):

High:

Low:

AvgT:

Pcpn:

San Juan

83.2ºF

72.1ºF

77.7ºF

4.57”

Saint Thomas

86.2ºF

73.2ºF

79.7ºF

2.74”

Saint Croix

85.0ºF

72.8ºF

78.9ºF

3.29”

December 2009 Observations:

High:

Low:

AvgT:

Pcpn:

San Juan

85.6ºF (+2.3ºF)

74.9ºF (+2.8ºF)

80.2ºF (+2.5ºF)

1.83” (-2.94”)

Saint Thomas

85.3ºF (-0.9ºF)

76.0ºF (+2.8ºF)

80.6ºF (+0.9ºF)

3.18” (+0.44”)

Saint Croix

85.6ºF (+0.6ºF)

74.2ºF (+1.4ºF)

79.9ºF (+1.0ºF)

2.19” (-1.10”)

December 2009 Extremes:

High:

Low:

San Juan

89ºF – December 20^th

71ºF – December 23^rd

Saint Thomas

89ºF – December 2^nd & 4^th

73ºF – December 22^nd & 29^th

Saint Croix

88ºF – December 11^th & 13^th

69ºF – December 30^th

December Historical Statistics:

Highest December Temperatures on record:

San Juan

94ºF – December 6^th, 1989

91ºF – December 24^th, 1995*

*Most recent occurrence

Saint Thomas

92ºF – December 26^th, 1995*

*Most recent occurrence

Saint Croix

92ºF – December 27^th, 1995

90ºF – December 10^th, 1998*

*Most recent occurrence

Lowest December Temperatures on record:

San Juan

63ºF – December 22^nd, 1964

64ºF – December 25^th, 1967*

*Most recent occurrence

Saint Thomas

62ºF – December 5^th, 1972

63ºF – December 24^th, 1991, December 7^th & 27^th, 1972

64ºF – December 10^th, 1982*

*Most recent occurrence

Saint Croix

61ºF – December 29^th, 1982 & December 24^th, 1964

62ºF – December 28^th, 1980

63ºF - December 26^th, 1991*

*Most recent occurrence

Wettest Decembers:

San Juan

16.81” December 1981

11.79” December 2001

10.00” December 1961

Saint Thomas

9.87” December 1960

7.45” December 1957

6.66” December 1981

Saint Croix

14.03” December 1960

9.07” December 1975

7.86” December 2001

Driest Decembers:

San Juan

0.68” December 1963

1.02” December 1997

1.83” December 2009

Saint Thomas

0.25” December 1985*

0.63” December 1963

1.76” December 1956

*4 days missing data

Saint Croix

0.75” December 2008

0.79” December 1963

0.89” December 1958

2000-2009 Decade in Review:

Decadal Observations for San Juan, Puerto Rico:

Decadal December High Temperatures:

2000’s		1990’s		1980’s		1970’s		1960’s		1950’s*
*83.8ºF*		*84.4ºF*		*84.5ºF*		*83.7ºF*		*83.3ºF*		*83.5ºF*

Decadal December Low Temperatures:

2000’s		1990’s		1980’s		1970’s		1960’s		1950’s*
*72.8ºF*		*72.5ºF*		*72.4ºF*		*73.3ºF*		*71.1ºF*		*69.5ºF*

Decadal December Average Temperatures:

2000’s		1990’s		1980’s		1970’s		1960’s		1950’s*
*78.3ºF*		*78.5ºF*		*78.4ºF*		*78.5ºF*		*77.2ºF*		*76.5ºF*

Decadal December Precipitation:

2000’s		1990’s		1980’s		1970’s		1960’s		1950’s*
*5.19”*		*4.08”*		*5.36”*		*4.57”*		*4.54”*		*4.84”*

* Records for San Juan began on January 1^st, 1956

Figure 2 - Temperature deviations for San Juan, PR

Figure 3 - Temperature deviations for Saint Thomas, VI

Figure 4 - Temperature deviations for Saint Croix, VI

Figure 5 - December precipitation deviations 2000's

Figure 6 - 2009 precipitation deviations for San Juan, Saint Thomas, and Saint Croix

Looking ahead toward the month of January:

Average January Temperatures/Precipitation (NCDC 1971-2000 averages):

High:

Low:

AvgT:

Pcpn:

San Juan

82.4ºF

70.8ºF

76.6ºF

3.02”

Saint Thomas

85.8ºF

72.0ºF

78.9ºF

1.89”

Saint Croix

84.3ºF

72.1ºF

78.2ºF

2.16”

Moon/Sun/Tide Data for the month of January:

The sun rises at 6:57 am AST on New Years morning and sets at 6:00 pm AST, in San Juan, Puerto Rico. This represents a total of 11 hours and 3 minutes of daylight. By January 31^st, the sun will rise at 6:58 am AST and set at 6:18 pm AST, providing a total of 11 hours and 20 minutes of daylight, or a total increase in 17 minutes over the course of the month. At Charlotte Amalie on Saint Thomas, the sun will rise at 6:52 am AST and set at 5:55 pm AST on the 1^st of the month. By the end of the month, the sun will rise at 6:53 am AST and set at 6:13 pm AST, also representing a total increase in daylight of 17 minutes for the month.

For the month of January, a full moon will be observed on the 30^th of the month at 2:18 am AST. There will also be a new moon on the 15^th of the month at 3:11 am AST. The last quarter of the moon will be observed on the 7^th of January and the first quarter of the new moon will be observed on the 23^rd of the month.

Links to additional sunrise/sunset data, phases of the moon, as well as tide data can all be found by clicking on the climate link of the National Weather Service San Juan homepage (www.srh.noaa.gov/sju) and then clicking on the Astronomical tab.

National Weather Service Weather Forecast Office