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 2nd, 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 4th 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 4th of the month to 97ºF in Ponce on the 3rd of May. Temperatures across the U.S. Virgin Islands ranged from 65ºF at Beth Upper New Works on Saint Croix, observed on May 5th and 8th, to 90ºF, also at Beth Upper New Works on Saint Croix, observed on May 26th, 28th and 29th. Other notable temperatures for May 2009 are listed below:
 

Other Notable May 2009 High Temps:            
 
93ºF in Rio Piedras on May 29th  
93ºF in Dos Bocas on May 28th
92ºF in San Juan on May 28th
92ºF in Rincon on May 28th               
92ºF in Corozal on May 31st
 
Other Notable May 2009 Low Temps:
 
60ºF in Toro Negro on May 4th  
61ºF in Maricao on May 4th  
61ºF in Aibonito on May 3rd  
62ºF in Trujillo Alto on May 19th  
 

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

 

  

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 28th    
73ºF – May 13th
 
Saint Thomas
88ºF – May 26th & 31st
72ºF – May 4th   
Saint Croix
88ºF – May 27th
71ºF – May 3rd

 
May Historical Statistics:
 
Highest May Temperatures on record:
 

San Juan              
96ºF – May 5th &11th, 1980
95ºF – Numerous Times     
Saint Thomas      
97ºF – May 23rd, 1996*
96ºF – May 28th, 1995*
*Most recent occurrence
Saint Croix
94ºF – May 28th, 1972
92ºF – May 25th, 1994*
*Most recent occurrence

 
Lowest May Temperatures on record:
 

San Juan              
66ºF – May 5th, 1962
67ºF – May 6th, 1962 &
           May 18th, 1957
Saint Thomas
66ºF – May 5th, 1974
68ºF – May 11th, 1986*
*Most recent occurrence
Saint Croix
63ºF – May 4th, 1992
64ºF – May 15th, 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 1st, 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 1st 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 30th, 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 1st 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 7th of the month at 2:12 pm AST. There will also be a new moon on the 22nd of the month at 3:35 pm AST. The first quarter of the moon was observed on May 31st and the last quarter of the moon will be observed on June 15th.
 
                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.

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