May 2009 Climate Report

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

May 2009 Highlights:

May 2009 marked the wettest month of the year so far across Puerto Rico. An island wide average rainfall of 7.66” was recorded for the month, which was amounted to almost 3” more than March, the second wettest month so far in 2009. While statistically speaking May is the second wettest month of the year across Puerto Rico, during May 2009, Puerto Rico received 127% of its normal precipitation. The wettest sectors of the island were the north coast and eastern interior, which both received 141% of their normal precipitation for the month. The western interior of the island received the least amount of rainfall in relation to normal, recording a 112% of its average May precipitation. Thanks to the above normal rainfall (122%) that has accumulated island wide over the first five months of the year, no sector of the island was classified as experiencing abnormally dry or drought conditions by the U.S. drought monitor as of June 2^nd, 2009. In addition, interestingly, all six sectors of the island have benefited nearly equally from above normal rainfall through May, having received between 109% and 130% of their normal rainfall year to date (YTD).

In San Juan, 5.28” of rain fell in May, which was 100% of the 30-year average. Across the US Virgin Islands, May precipitation totals on Saint Thomas and Saint Croix varied from 106% to 60% of normal during the month, respectively. While San Juan (103%) and Saint Thomas (119%) have both received above normal precipitation YTD, the island of Saint Croix has not fared as well, having received only 54% of its normal rainfall YTD. In fact, this marks the 4^th driest start to the year on record for Saint Croix (6.22”), with only 1977 (4.79”), 1991 (5.69”), and 2005 (6.14”) starting off drier.

Temperatures across Puerto Rico ranged from 54ºF in Adjuntas on the 4^th of the month to 97ºF in Ponce on the 3^rd of May. Temperatures across the U.S. Virgin Islands ranged from 65ºF at Beth Upper New Works on Saint Croix, observed on May 5^th and 8^th, to 90ºF, also at Beth Upper New Works on Saint Croix, observed on May 26^th, 28^th and 29^th. Other notable temperatures for May 2009 are listed below:

Other Notable May 2009 High Temps:

93ºF in Rio Piedras on May 29^th

93ºF in Dos Bocas on May 28^th

92ºF in San Juan on May 28^th

92ºF in Rincon on May 28^th

92ºF in Corozal on May 31^st

Other Notable May 2009 Low Temps:

60ºF in Toro Negro on May 4^th

61ºF in Maricao on May 4^th

61ºF in Aibonito on May 3^rd

62ºF in Trujillo Alto on May 19^th

The highest 24-hour precipitation total for the month of May was 4.45”, which fell in Cacaos Orocovis on the 9^th of the month. The highest weekly rainfall total occurred in Toro Negro, where 8.69” of rainfall accumulated the week ending May 15^th.

Figure 1A – Island wide precipitation forJanuary-May 2009

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

Monthly Weather Summary:

May is one of the wetter months across Puerto Rico and the U.S. Virgin Islands. During the month of May, the Luis Muñoz International Airport in San Juan typically receives 5.29” of rainfall on average, with a record of 14.99” accumulating in May 1965. The driest May on record was May 1972, when 0.44” of rainfall was recorded in San Juan. The average temperature at the Luis Muñoz International Airport in San Juan for May is 80.6ºF, 1.5 ºF warmer than April. Across the U.S. Virgin Islands, 3.36” of rainfall normally accumulates on Saint Thomas and 3.62” of rainfall normally falls on Saint Croix. Average temperatures on both islands for the month typically vary between 81.9ºF and 81.7ºF on Saint Thomas and Saint Croix, respectively.

May 2009 was a rather wet month for the local islands. A fairly persistent area of upper level troughiness dominated the southwestern Atlantic and much of the Eastern Caribbean Sea. This brought a humid trade wind flow to Puerto Rico resulting in 21 days of measurable precipitation in San Juan. A few surface low pressure systems developed very close to the local area, enabling deep tropical moisture to be drawn over the islands, resulting in heavy rainfall. By the second half of May, high temperatures were over 85 degrees most afternoons. In Puerto Rico, a transition to afternoon convection, or wet season shower and thunderstorm activity over Western Puerto Rico generally occurs in April or May. Once maximum temperatures are high enough and the ITCZ begins to lift north enough, they change the subsident winter time flow to a generally unstable summer time atmosphere. This allows heavy rainfall to form each afternoon over portions of the western part of the main island due to island breeze convergence. By late May, this pattern was firmly in place allowing for accumulations of heavy rains each afternoon over parts of western Puerto Rico.

May 2009 Statistics:

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

High:

Low:

AvgT:

Pcpn:

San Juan

86.3 ºF

74.9ºF

80.6ºF

5.29”

Saint Thomas

87.9ºF

75.9ºF

81.9ºF

3.36”

Saint Croix

87.5ºF

75.9ºF

81.7ºF

3.62”

May 2009 Observations:

High:

Low:

AvgT:

Pcpn:

San Juan

85.3ºF (-1.0ºF)

75.9ºF (+1.0ºF)

80.6ºF (+0.0ºF)

5.28” (-0.01”)

Saint Thomas

84.7ºF (-3.2ºF)

75.8ºF (-0.1ºF)

80.2ºF (-1.7ºF)

3.55” (+0.19”)

Saint Croix

85.3ºF (-2.2ºF)

75.9ºF (0.0ºF)

80.6ºF (-1.1ºF)

2.19” (-1.43”)

May 2009 Extremes:

High:

Low:

San Juan

92ºF – May 28^th

73ºF – May 13^th

Saint Thomas

88ºF – May 26^th & 31^st

72ºF – May 4^th

Saint Croix

88ºF – May 27^th

71ºF – May 3^rd

May Historical Statistics:

Highest May Temperatures on record:

San Juan

96ºF – May 5^th &11^th, 1980

95ºF – Numerous Times

Saint Thomas

97ºF – May 23^rd, 1996*

96ºF – May 28^th, 1995*

*Most recent occurrence

Saint Croix

94ºF – May 28^th, 1972

92ºF – May 25^th, 1994*

*Most recent occurrence

Lowest May Temperatures on record:

San Juan

66ºF – May 5^th, 1962

67ºF – May 6^th, 1962 &

May 18^th, 1957

Saint Thomas

66ºF – May 5^th, 1974

68ºF – May 11^th, 1986*

*Most recent occurrence

Saint Croix

63ºF – May 4^th, 1992

64ºF – May 15^th, 1975 & 1972

Wettest Mays:

San Juan

14.99” May 1965

13.59” May 1958

12.80” May 1986

Saint Thomas

16.39” May 1960

9.98” May 1979

9.80” May 1987

Saint Croix

14.03” May 1981

11.38” May 2001

8.89” May 1987

Driest Mays:

San Juan

0.44” May 1972

0.48” May 1973

1.04” May 1975

Saint Thomas

0.06” May 2008

0.28” May 2007

0.47” May 1973

Saint Croix

0.22” May 1974

0.28” May 2005

0.37” May 2003

2000-2009 Decade in Review:

Decadal Observations for San Juan, Puerto Rico:

Decadal May High Temperatures:

2000’s		1990’s		1980’s		1970’s		1960’s		1950’s*
*87.4ºF*		*87.8ºF*		*88.2ºF*		*87.4ºF*		*86.0ºF*		*85.4ºF*

Decadal May Low Temperatures:

2000’s		1990’s		1980’s		1970’s		1960’s		1950’s*
*75.6ºF*		*75.4ºF*		*75.0ºF*		*75.0ºF*		*73.2ºF*		*71.9ºF*

Decadal May Average Temperatures:

2000’s		1990’s		1980’s		1970’s		1960’s		1950’s*
*81.5ºF*		*81.6ºF*		*81.6ºF*		*81.2ºF*		*79.6ºF*		*78.6ºF*

Decadal May Precipitation:

2000’s		1990’s		1980’s		1970’s		1960’s		1950’s*
*5.02”*		*4.35”*		*7.59”*		*4.25”*		*6.41”*		*8.13”*

* 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 – May precipitation deviations 2000's

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

Looking ahead toward the month of June:

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

High:

Low:

AvgT:

Pcpn:

San Juan

87.6ºF

76.6ºF

82.1ºF

3.52”

Saint Thomas

89.5ºF

77.4ºF

83.5ºF

2.35”

Saint Croix

88.6ºF

78.1ºF

83.4ºF

2.30”

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

The sun rises at 5:47 am AST on the 1^st of June and sets at 6:58 pm AST, in San Juan, Puerto Rico. This represents a total of 13 hours and 11 minutes of daylight. By June 30^th, the sun will rise at 5:52 am AST and set at 7:05 pm AST, providing a total of 13 hours and 13 minutes of daylight, or a total increase of 2 minutes over the course of the month. The sunset time of 7:05 pm AST is the latest the sun will set in San Juan all year long. At Charlotte Amalie on Saint Thomas, the sun will rise at 5:43 am AST and set at 6:53 pm AST on the 1^st of the month. By the end of the month, the sun will rise at 5:47 am AST and set at 7:00 pm AST, representing a total increase of 3 minutes of daylight for the month.

For the month of June, a full moon will be observed on the 7^th of the month at 2:12 pm AST. There will also be a new moon on the 22^nd of the month at 3:35 pm AST. The first quarter of the moon was observed on May 31^st and the last quarter of the moon will be observed on June 15^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.srh.noaa.gov/sju) and then clicking on the Astronomical tab.

National Weather Service Weather Forecast Office