March 2009 Climate Report

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

March 2009 Highlights:

March 2009 marked the third consecutive month of above normal precipitation island wide across Puerto Rico. By the end of the month, 158% of the normal precipitation had accumulated across the array of climatological stations on the island. Including the above normal precipitation that fell over the first two months of the year, 137% of the normal precipitation has fallen island wide year to date (YTD). In San Juan, 3.21” of rain fell in March, which was 150% of the 30-year average. Across the US Virgin Islands, March precipitation totals on Saint Croix and Saint Thomas varied from 57% to 180% of normal during the month, respectively.

Temperatures across Puerto Rico ranged from 45ºF in Adjuntas on the 28^th of the month to 90ºF in Central Aguirre, Dos Bocas and on Magueyes Island, on 27^th, 3^rd and 9^th of the month, respectively. Temperatures across the U.S. Virgin Islands ranged from 62ºF at Beth Upper New Works on Saint Croix, observed on numerous days, to 87ºF, also at Beth Upper New Works on Saint Croix, observed on March 23^rd. Other notable temperatures for March 2009 are listed below:

Notable March 2009 High Temps:

90ºF in Central Aguirre on March 27^th

90ºF at Dos Bocas on March 3^rd

90ºF on Magueyes Island on March

89ºF in Guayama on March 26^th

89ºF in Ponce on March 13^th, 27^th & 28^th

89ºF in Rio Piedras on March 24^th

Notable March 2009 Low Temps:

45ºF in Adjuntas on March 28^th

53ºF in Aibonito on March 9^th

54ºF in Cerro Maravilla on March 1^st & 7^th

54ºF in Toa Negro on March 27^th

56ºF in Lajas on March 9^th

56ºF in Maricao on March 27^th

56ºF in Ponce on March 9^th

The highest 24-hour precipitation total for the month of March was 4.50”, which fell in Trujillo Alto on the 5^th of March. The highest weekly rainfall total occurred at Cerro Maravilla, where 10.47” of rainfall accumulated the week ending March 6^th. Island wide precipitation for Puerto Rico is plotted by island sector and displayed below.

Figure 1 – Island wide precipitation forJanuary-March 2009

Monthly Weather Summary:

On average, the month of March is the driest month of the year across Puerto Rico, with March 2005 marking the only month since 1956 when no rainfall accumulated at the Luis Muñoz International Airport in San Juan. On average, the airport receives only 2.17” inches of rain during the month of March, which is far shy of the 6.00” that normally accumulates in November, the wettest month of the year. March is also one of the cooler months on the island, with an average daily temperature of 78.0 ºF observed in San Juan, 1.2 ºF warmer than January, the coolest month of the year, yet 4.8 ºF cooler than August, the warmest month.

March 2009 will be remembered by two cold fronts that dissipated across the local islands, the first on the 5^th of the month and the 2^nd on the 23^rd of the month. Large spikes in island wide precipitation can be seen in Figure 1 during the 9^th and 12^th weeks of the year correspondingly. The remainder of March was fairly quiet and lived up to its dry season reputation, with a relatively stable airmass parked over the region and only patchy low level moisture advecting across the local islands from time to time, bringing an occasional shower or two. However, due to heavy rainfall associated with the two frontal boundaries that impacted the island during the month, 158% of the normal precipitation accumulated island wide this March, with the Luis Muñoz International Airport in San Juan recording 150% of its normal precipitation. Overall temperatures in San Juan ended up the month being nearly identical to the 30-year average for the month, while temperatures across the U.S. Virgin islands were significantly cooler than average, with Saint Croix and Saint Thomas observing average temperatures 2.0ºF and 3.0ºF cooler than average, respectively.

March 2009 Statistics:

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

High:

Low:

AvgT:

Pcpn:

San Juan

83.4ºF

71.7ºF

77.6ºF

2.14”

Saint Thomas

86.5ºF

72.5ºF

79.5ºF

1.52”

Saint Croix

85.0ºF

72.3ºF

78.7ºF

1.80”

March 2009 Observations:

High:

Low:

AvgT:

Pcpn:

San Juan

82.7ºF (-0.7ºF)

72.4ºF (+0.7ºF)

77.5ºF (-0.1ºF)

3.21” (+1.03”)

Saint Thomas

81.6ºF (-4.9ºF)

71.5ºF (-1.0ºF)

76.5ºF (-3.0ºF)

2.74” (+1.22”)

Saint Croix

82.9ºF (-2.1ºF)

70.6ºF (-1.7ºF)

76.7ºF (-2.0ºF)

1.03” (-1.14”)

March 2009 Extremes:

High:

Low:

San Juan

88ºF – March 3^rd

70ºF – March 21^st & 27^th

Saint Thomas

85ºF – March 29^th

69ºF – March 14^th & 19^th

Saint Croix

85ºF – March 31^st

66ºF – March 12^th

March Historical Statistics:

Highest March Temperatures on record:

San Juan

96ºF – March 19^th, 1983

95ºF – March 30^th, 1984

94ºF – Numerous Times

Saint Thomas

94ºF – March 21^st, 26^th &

March 27^th, 1994

93ºF – March 25^th, 1994 &

March 31^st, 1996

Saint Croix

92ºF – March 5^th, 1996

91ºF – March 31^st, 1972 &

March 20, 21 & 24, 1973

Lowest March Temperatures on record:

San Juan

60ºF – March 3^rd, 1967

61ºF – March 23^rd, 1962 &

March 6^th, 1970

62ºF – Numerous Times

Saint Thomas

56ºF – March 11^th, 1972

59ºF – March 27^th, 1972

60ºF – March 1^st & 30^th, 1972

61ºF – March 29^th, 1972

Saint Croix

60ºF – March 29^th, 1977

62ºF – Numerous Times

Wettest Marches:

San Juan

5.41” March 1958

5.17” March 1987

4.83” March 1956

Saint Thomas

4.37” March 1961

3.95” March 1975

3.73” March 1963

Saint Croix

4.15” March 1985

3.41” March 1972

3.31” March 1988

Driest Marches:

San Juan

0.00” March 2005

0.58” March 2008

0.72” March 1970

Saint Thomas

0.00” March 2006

0.01” March 1980, 2003 &

March 2008

Saint Croix

0.17” March 1951

0.29” March 2003

0.39” March 2005

2000-2009 Decade in Review:

For the city of San Juan, March 2009 was the second coolest March of the past decade, with the average temperature of 77.5ºF being 0.1ºF cooler than the 30-year average. Across the U.S. Virgin Islands, temperatures on both Saint Thomas and Saint Croix were both well below average, with readings of 3.0ºF and 2.0ºF below their 30-year averages on Saint Thomas and Saint Croix, respectively. The 2.0ºF temperature deviation on Saint Croix represented the coolest March of the decade and the 3.0ºF temperature deviation on Saint Thomas was tied for the coolest March of the decade. A graphical depiction of the temperature deviations across San Juan, Saint Thomas and Saint Croix can been seen in Figures 2-4.

Figure 2 – Temperature deviations for San Juan, PR

Figure 3 – Temperature deviations for Saint Thomas, VI

Figure 4 – Temperature deviations for Saint Croix, VI

Thirteen weeks into 2009, Puerto Rico was running well above normal, precipitation wise, having received 137% of its normal rainfall YTD. All six sectors of the island have enjoyed above normal precipitation thus far, ranging from 104% along the southern slopes to 183% along the south coast. Across the Virgin Islands, Saint Thomas has received 164% of its yearly rainfall, while Saint Croix has been significantly drier, having received only 41% of their normal rainfall YTD. The 8.04” of rainfall Saint Thomas has received YTD represents the 4^th wettest start to the year on record, while the 2.44” of rainfall Saint Croix has received YTD represents their driest start to the year on record. March precipitation deviations for San Juan, Saint Thomas, and Saint Croix can be found in Figure 5, and YTD precipitation deviations can be found in figure 6.

Figure 5 – March precipitation deviation 2000’s

Figure 6 – Year-to-Date precipitation deviations for San Juan, Saint Thomas, and Saint Croix

Decadal Observations for San Juan, Puerto Rico:

Decadal March High Temperatures:

2000’s		1990’s		1980’s		1970’s		1960’s		1950’s*
*84.8ºF*		*84.8ºF*		*85.4ºF*		*84.3ºF*		*83.9ºF*		*84.8ºF*

Decadal March Low Temperatures:

2000’s		1990’s		1980’s		1970’s		1960’s		1950’s*
*72.4ºF*		*71.4ºF*		*71.9ºF*		*72.4ºF*		*70.2ºF*		*67.9ºF*

Decadal March Average Temperatures:

2000’s		1990’s		1980’s		1970’s		1960’s		1950’s*
*78.6ºF*		*78.1ºF*		*78.6ºF*		*78.4ºF*		*77.0ºF*		*76.4ºF*

Decadal March Precipitation:

2000’s		1990’s		1980’s		1970’s		1960’s		1950’s*
*1.57”*		*1.82”*		*2.29”*		*2.32”*		*2.37”*		*3.27”*

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

Looking ahead toward the month of April:

The month of April is generally a transition month between the dry and wet seasons here in Puerto Rico, with some years being very wet and some being very dry. In fact, the wettest April on record in San Juan was April 2005, when 15.00” of rainfall accumulated at the Luis Muñoz International Airport, and the driest April on record was 1997, when only 0.08” of rainfall accumulated. On average, April ranks as the 5^th driest month of the year, with an average rainfall of 3.71” recorded in San Juan each year. Due to above average rainfall island wide YTD, by the end of March, no sector of the island was classified as experiencing abnormally dry or drought conditions by the U.S. Drought Monitor.

Looking ahead, with La Niña conditions weakening and ENSO neutral conditions expected to continue, we can expect temperature trends to be slightly above normal and precipitation trends to be slightly below normal over the coming months (as suggested by previous climatological studies for the northeastern Caribbean). Additional information about current ENSO conditions as well as additional climate information can be found from the Climate Prediction Center.

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

High:

Low:

AvgT:

Pcpn:

San Juan

84.9ºF

73.2ºF

79.1ºF

3.71”

Saint Thomas

87.6ºF

73.9ºF

80.8ºF

2.39”

Saint Croix

86.2ºF

74.0ºF

80.1ºF

2.00”

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

The sun rises at 6:19 am AST on the 1^st of April and sets at 6:38 pm AST, in San Juan, Puerto Rico. This represents a total of 12 hours and 19 minutes of daylight. By April 30^th, the sun will rise at 5:58 am AST and set at 6:46 pm AST, providing a total of 12 hours and 48 minutes of daylight, or a total increase of 29 minutes over the course of the month. At Charlotte Amalie on Saint Thomas, the sun will rise at 6:14 am AST and set at 6:33 pm AST on the 1^st of the month. By the end of the month, the sun will rise at 5:53 am AST and set at 6:41 pm AST, representing a total increase of 31minutes of daylight for the month.

For the month of April, a full moon will be observed on the 20^th of the month at 6:25 am AST. There will also be a new moon on the 5^th of the month at 11:55 pm AST. The first quarter of the moon will be observed on the 12^th and the last quarter of the moon will be observed on the 28^th.

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.weather.gov/sju) and then clicking on the Astronomical tab.

National Weather Service Weather Forecast Office