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 28th of the month to 90ºF in Central Aguirre, Dos Bocas and on Magueyes Island, on 27th, 3rd and 9th 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 23rd. Other notable temperatures for March 2009 are listed below:
 
Notable March 2009 High Temps:   
 
90ºF in Central Aguirre on March 27th
90ºF at Dos Bocas on March 3rd
90ºF on Magueyes Island on March
89ºF in Guayama on March 26th       
89ºF in Ponce on March 13th, 27th & 28th
89ºF in Rio Piedras on March 24th
 
Notable March 2009 Low Temps:
 
45ºF in Adjuntas on March 28th
53ºF in Aibonito on March 9th
54ºF in Cerro Maravilla on March 1st & 7th
54ºF in Toa Negro on March 27th
56ºF in Lajas on March 9th
56ºF in Maricao on March 27th
56ºF in Ponce on March 9th
 
The highest 24-hour precipitation total for the month of March was 4.50”, which fell in Trujillo Alto on the 5th of March. The highest weekly rainfall total occurred at Cerro Maravilla, where 10.47” of rainfall accumulated the week ending March 6th. 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 5th of the month and the 2nd on the 23rd of the month. Large spikes in island wide precipitation can be seen in Figure 1 during the 9th and 12th 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 3rd  
70ºF – March 21st & 27th
 
Saint Thomas
 85ºF – March 29th
69ºF – March 14th & 19th 
Saint Croix
85ºF – March 31st
66ºF – March 12th
 
March Historical Statistics:
 
Highest March Temperatures on record:
 
San Juan              
96ºF – March 19th, 1983
95ºF – March 30th, 1984      
94ºF – Numerous Times     
Saint Thomas      
94ºF – March 21st, 26th &
March 27th, 1994                  
93ºF – March 25th, 1994 &  
March 31st, 1996
Saint Croix
92ºF – March 5th, 1996
91ºF – March 31st, 1972 &
March 20, 21 & 24, 1973
 
Lowest March Temperatures on record:
 
San Juan              
60ºF – March 3rd, 1967
61ºF – March 23rd, 1962 &  
March 6th, 1970    
62ºF – Numerous Times
Saint Thomas
56ºF – March 11th, 1972      
59ºF – March 27th, 1972      
60ºF – March 1st & 30th, 1972
61ºF – March 29th, 1972
Saint Croix
60ºF – March 29th, 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 4th 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 1st, 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 5th 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 1st 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 30th, 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 1st 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 20th of the month at 6:25 am AST. There will also be a new moon on the 5th of the month at 11:55 pm AST. The first quarter of the moon will be observed on the 12th and the last quarter of the moon will be observed on the 28th.
 
                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.
 
 

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