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PUERTO RICO AND THE U.S. VIRGIN ISLANDS

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Puerto Rico
Photo by Breezy Baldwin

PUERTO RICO AND THE U.S. VIRGIN ISLANDS

Puerto Rico and the U.S. Virgin Islands are located in the subtropical Caribbean region. Puerto Rico comprises the main island and several smaller nearby islands, including Vieques, Culebra, Isla de Mona, Caja de Muertos, and Isla Desecheo. The major islands of the U.S. Virgin Islands are St. Thomas, St. Croix, and St. John. Surrounded by ocean on all sides, the islands experience warm and humid tropical conditions with minimal temperature variations between seasons. The temperate climate of San Juan, Puerto Rico, illustrates the tropical conditions of these islands. The annual average temperature is 81.0°F. Temperatures are generally cooler in January, with an average minimum temperature of 72.0°F and an average maximum temperature of 83.2°F, and warmer in August, with an average minimum temperature of 78.2°F and an average maximum temperature of 89.2°F.

Figure 1

Observed and Projected Temperature Change

VIEW

Observed and projected changes (compared to the 1951–1980 average) in near-surface air temperature for Puerto Rico. Observed data are for 1950–2017, based on data from six long-term reporting sites. Projected changes for 2006–2100 are from global climate models for two possible futures: one in which greenhouse gas emissions continue to increase (higher emissions) and another in which greenhouse gas emissions increase at a slower rate (lower emissions)1. Temperatures in Puerto Rico (orange line) have risen by more than 1.5°F since the beginning of the 20th century. Shading indicates the range of annual temperatures from the set of models. Observed temperatures are generally within the envelope of model simulations of the historical period (gray shading). Historically unprecedented warming is projected during the 21st century. Less warming is expected under a lower emissions future (the coldest years being about as warm as the hottest year in the historical record; green shading), and more warming is expected under a higher emissions future (the hottest years being about 7ºF warmer than the hottest year in the historical record; red shading). Source: CICS-NC and NOAA NCEI.

Precipitation across Puerto Rico and the U.S. Virgin Islands varies seasonally, with wetter summers and relatively drier winters. The predominant synoptic influence on the islands’ climate is the North Atlantic subtropical high, which causes prevailing trade winds predominantly from the east and northeast. The east to west positioning of the Cordillera Central (the highest elevation is 4,390 feet) provide a natural divide that separates Puerto Rico into two climatologically distinct regions. The northern two-thirds of Puerto Rico has a mostly humid climate, and the southern portion has a drier, semiarid climate. The northeast trade winds provide water vapor for precipitation along the northern coast and outlying islands, but passage over this mountain range removes moisture through precipitation, and the resulting downslope flow is drier. The U.S. Virgin Islands are not as high in elevation (the highest point is 1,555 feet on St. Thomas), but topographic effects on precipitation still occur, with the west (upwind) sides being wetter than the east (downwind) sides.

The islands warmed throughout the 20th and early 21st centuries. For example, temperatures in San Juan have increased by more than 1.5°F since 1950 (Figure 1). The number of very hot days (days with a maximum temperature exceeding 95°F) does not exhibit any trend (Figure 2). By contrast, extremely warm nights (days with a minimum temperature exceeding 80°F) have generally been above average since 2000, with the highest number occurring since 2015 (Figure 3). The urban heat island effect has caused temperatures to rise faster in San Juan than across the rest of the islands. The surface temperatures of the surrounding ocean area provide an essential regulator on temperatures in Puerto Rico and the U.S. Virgin Islands and have risen by approximately 3°F since 1910 (Figure 4).

Observed Number of Very Hot Days

Observed Number of Very Hot Days

Figure 2: The observed annual number of very hot days (days with maximum temperature above 95°F) for 1950–2017, averaged over 5-year periods (the last period, 2015–2017, is only three years and indicated by the hatching); these values are averages from five long-term reporting sites in Puerto Rico and one in the U.S. Virgin Islands. There is no overall trend. The dark horizontal line is the long-term average (1950–2017) of 2.5 days per year. Source: CICS-NC and NOAA NCEI.

Observed Number of Extremely Warm Nights

Observed Number of Extremely Warm Nights

Figure 3: The observed annual number of extremely warm nights (days with minimum temperature above 80°F) for 1950–2017, averaged over 5-year periods (the last period, 2015–2017, is only three years and indicated by the hatching); these values are averages from five long-term reporting sites in Puerto Rico and one in the U.S. Virgin Islands. Since 2000, the islands have experienced an above-average number of such events, with the largest number occurring since 2015. The dark horizontal line is the long-term average (1950–2017) of 9.3 days per year. Source: CICS-NC and NOAA NCEI.

Change in Annual Sea Surface Temperature

Change in Annual Sea Surface Temperature

Figure 4: Observed changes for 1900–2017 (compared to the 1951–1980 average) in annual average sea surface temperature (SST) for the region surrounding Puerto Rico and the U.S. Virgin Islands (62°W–68°W, 17°N–19°N). Source: CICS-NC and NOAA NCEI.

Annual precipitation for Puerto Rico ranges from 172 inches near El Yunque National Forest (located in the Sierra de Luquillo mountains) in the eastern part of the island to less than 30 inches at Ponce in the southwest. Annual rainfall in the U.S. Virgin Islands is less than 50 inches across all the islands. Much of the rainfall in the wet season (May through October) derives from tropical cyclones (hurricanes and tropical storms) and easterly waves, which move from east to west, while high sea surface temperatures can also trigger local thunderstorm activity. In the dry season (November through April), rainfall is caused by cold fronts moving from west to east. Annual precipitation in Puerto Rico varies from year to year. Precipitation totals have been near to above-average since 1955, with only two periods experiencing much below average conditions (Figure 5).

Observed Annual Precipitation

Observed Annual Precipitation

Figure 5: The observed annual precipitation for 1955–2017, averaged over 5-year periods (the last period, 2015–2017, is only three years and indicated by the hatching); these values are averages from 11 long-term reporting stations in Puerto Rico. Annual precipitation in Puerto Rico varies from year to year. Precipitation totals have been near to above average since 1955, with only two periods experiencing much below average conditions. The dark horizontal line is the long-term average (1955–2017) of 61 inches per year. Source: CICS-NC and NOAA NCEI.

Heavy precipitation across the region has increased since the 1950s. The largest number of extreme precipitation events (days with precipitation greater than 3 inches; Figure 6) has occurred in recent years. In 2011, Puerto Rico and the U.S. Virgin Islands experienced an extended period of heavy rainfall and flooding (not associated with a tropical cyclone) during mid-May through mid-June, in which several locations recorded 2-4 times their normal rainfall during this period. Significant flooding occurred across Puerto Rico, with the exception of the southwest region of the island. Major flooding was also reported in Saint Croix, U.S. Virgin Islands, where weekly rainfall totals were on the order of 6 to 7 inches.

Observed Number of Extreme Precipitation Events

Observed Number of Extreme Precipitation Events

Figure 6: The observed number of annual extreme precipitation events (days with precipitation greater than 3 inches) for 1950–2017, averaged over 5-year periods (the last period, 2015–2017, is only three years and indicated by the hatching); these values are averages from 11 long-term reporting stations in Puerto Rico and 2 in the U.S. Virgin Islands. The largest number of such events has occurred since 2000. The dark horizontal line is the long-term average (1950–2017) of 1.4 days per year. Source: CICS-NC and NOAA NCEI.

Tropical cyclone events (hurricanes, tropical storms, and tropical depressions) are an important concern for the islands due to their position in the Caribbean hurricane belt. While such weather systems occur near the islands only about once every 2 years (Figure 7), they can have devastating impacts. Tropical cyclones affecting Puerto Rico and the U.S. Virgin Islands in the 21st century include, but are not limited to, Tropical Storm Jeanne in 2004, Hurricane Irene (Category 1) in 2011, and Hurricane Irma (Category 5) in 2017. Hurricane Irene produced very heavy rainfall that resulted in major flooding in northeast Puerto Rico. In the late 20th century, Hurricane Hugo (Category 4) in 1989, Hurricane Marilyn (Category 2) in 1995, and Hurricane Georges (Category 3) in 1998 all caused catastrophic damage to the islands. Earlier hurricanes of note include the San Felipe Segundo storm (Category 5) of 1928 and the San Ciprian storm (Category 4) of 1932. The two most devastating hurricanes occurred in 1899 and 2017. The 1899 San Ciriaco hurricane (Category 4), the most severe natural disaster recorded in the islands’ history, resulted in 3,300 deaths. In addition, a quarter of residents were left homeless, and more than $7 million in coffee production was destroyed (estimated at $225 million in 2012 dollars). Hurricane Maria (Category 4) made landfall in Puerto Rico in September 2017, causing devastating destruction across the islands. Winds that locally reached Category 5 intensity, combined with extremely heavy rainfall and the destructive power of wave action and storm surge, led to extensive damage to buildings and infrastructure. Severe flooding and mudslides affected much of Puerto Rico and the U.S. Virgin Islands, and most residents lost power for months during the largest power outage in American history. Maria is the third costliest hurricane in U.S. history, with total damages across the islands estimated at $90 billion (2017 dollars).

Figure 7

Total Tropical Cyclone Events in Puerto Rico, 1855-2017

VIEW

Total number of tropical cyclone events (including hurricanes, tropical storms, and tropical depressions) within 200 nautical miles of Puerto Rico, summed over 5-year periods (the last period, 2015–2017, is only three years and indicated by the hatching). Source: NOAA.

Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century (Figure 1). Even under a pathway of lower greenhouse gas emissions, annual average temperatures are projected to most likely exceed historical record levels by the middle of the 21st century. However, there is a large range of temperature increases under both pathways, and under the lower pathway, a few projections are only slightly warmer than historical records. Increases in the number of extremely hot days and warm nights are projected to accompany the overall warming.

Projected Change in Annual Precipitation

Projected Change in Annual Precipitation

Figure 8: Projected changes in annual precipitation (%) for the middle of the 21st century compared to the late 20th century under a higher emissions pathway. Total annual precipitation is projected to decrease in both Puerto Rico and the U.S. Virgin Islands. Hatching indicates areas where the changes are less than the standard deviation of the 20-year means from control simulations. The areas that are just shaded are where the changes are between one and two standard deviations of the 20-year means. Whited-out areas indicate that less than 90% of the models agree on the direction (increasing or decreasing) of the change. Source: CICS-NC, NOAA NCEI, and NEMAC.

A decrease in average annual precipitation is projected over the 21st century (Figure 8). Model projections indicate a decrease in precipitation averaging around 10%, however, there is significant uncertainty in the magnitude of precipitation changes in the Southern Caribbean region. Puerto Rico and the U.S. Virgin Islands may face an increased risk of drought, potentially affecting water supplies, agriculture, and the economy.

Although overall precipitation is projected to decrease, extreme precipitation events are projected to increase due to increased water vapor available in response to climate-change-related warming of ocean temperatures. While there is uncertainty in whether there will be a fewer or greater number of total hurricanes in the future, hurricane rainfall rates, storm surge heights due to sea level rise, and the number of major (Category 3, 4, and 5) hurricanes are all projected to increase.

Since 1962, the sea level at San Juan has risen by 0.6 inches per decade (close to the global sea level rise rate of 0.7 inches per decade). Sea level rise is an important concern in Puerto Rico due to its extensive coastline. Approximately 60% of Puerto Rico’s population lives within the islands’ 44 coastal cities, and these areas are also home to a significant share of the islands’ critical coastal infrastructure. Sea level rise has contributed to significant coastal erosion, resulting in the retreat of the Puerto Rican coastline of up to 3.3 feet per year (1.0 m/year). Even marginal amounts of sea level rise increase the likelihood of less common flooding events by amplifying tidal and storm surge. Most of the U.S. Virgin Islands are well above sea level; however, waterfront property in the capital, Charlotte Amalie, is generally within a few feet of sea level.

Global sea level is projected to rise between 1.0 and 8.2 feet by 2100 as a result of both past and future emissions from human activities (Figure 9), and similar rises are likely for Puerto Rico and the U.S. Virgin Islands. Some island-level estimates for Puerto Rico project a rise of up to 2.1 feet by 2060 and 4.9 feet by 2100 (Figure 10). Rising sea levels will likely result in increased coastal flooding, coastal erosion, and disruptions to coastal ecosystems and critical infrastructures.

Projected Change in Global Sea Level

Projected Change in Global Sea Level

Figure 9: Global mean sea level (GMSL) change from 1800 to 2100. Projections include the six U.S. Interagency Sea Level Rise Task Force GMSL scenarios (navy blue, royal blue, cyan, green, orange, and red curves) relative to historical geological, tide gauge and satellite altimeter GMSL reconstructions from 1800–2015 (black and magenta lines) and the very likely ranges in 2100 under both lower and higher emissions futures (teal and dark red boxes). Global sea level rise projections range from 1.0 to 8.2 feet by 2100. Source: Adapted from Sweet et al. 2017.

Projected Change in Sea Level for San Juan, PR

Projected Change in Sea Level for San Juan, PR

Figure 10: Relative sea level change for San Juan, PR from 1992 to 2150. These U.S. Army Corps of Engineers’ (USACE) sea level change curves are computed using the historic global mean sea level (GMSL) change rate of 1.7 mm/year, NOAA tide gauge data for San Juan, Puerto Rico (1.65 mm/year rise since 1962), and the estimated local vertical land movement rates of −0.02 mm/year for San Juan. All scenarios start in 1992 which corresponds to the midpoint of the current National Tidal Datum Epoch of 1983–2001. These island-level estimates of sea level for Puerto Rico project a rise of up to 2.1 feet by 2060 and 4.9 feet by 2100. Source: Adapted from PRCCC 2013.

 
Lead authors:
Jennifer Runkle, Kenneth E. Kunkel, Laura E. Stevens
Contributing authors:
Sarah Champion, David Easterling, Adam Terando, Liqiang Sun, Brooke C. Stewart, Glenn Landers
Recommended Citation:
Runkle, J., K. Kunkel, and L. Stevens, 2018: Puerto Rico and the U.S. Virgin Islands State Climate Summary. NOAA Technical Report NESDIS 149-PR, 4 pp.
 

Resources

  1. Avila, L.A., and J. Cangialosi, 2011: Tropical Cyclone Report: Hurricane Irene (AL092011). National Hurricane Center. [Available online at http://www.nhc.noaa.gov/data/tcr/AL092011_Irene.pdf]
  2. Bush, D.M., R.M.T. Webb, J.G. González Liboy, L. Hyman, and W.J. Neal, 1995: Living with the Puerto Rico Shore. Duke University Press, Durham, NC.
  3. EPA, 2016: What climate change means for Puerto Rico, EPA 430-F-16-063, United States Environmental Protection Agency, 2 pp. [Available online at https://www.epa.gov/sites/production/files/2016-09/documents/climate-change-pr.pdf]
  4. EPA, 2016: What climate change means for the U.S. Virgin Islands, EPA 430-F-16-065, United States Environmental Protection Agency, 2 pp. [Available online at https://www.epa.gov/sites/production/files/2016-11/documents/climate-change-usvi.pdf]
  5. Jury, M.R., S. Chiao, and E.W. Harmsen, 2009: Mesoscale Structure of Trade Wind Convection over Puerto Rico: Composite Observations and Numerical Simulation. Boundary-Layer Meteorology, 132, 289-313, doi: 10.1007/s10546-009-9393-3.
  6. Jury, M.R., R. Rios-Berrios, and E. Garcia. 2011: Caribbean hurricanes: changes of intensity and track prediction. Theoretical Applied Climatology, 107, 297-311. doi: 10.1007/s00704-011-0461-5.
  7. Knutson, T.R., J. McBride, J. Chan, K.A. Emanuel, G.J. Holland, C. Landsea, I. Held, J. P. Kossin, A. K. Srivastava, and M. Sugi, 2010: Tropical Cyclones and Climate Change. Nature Geoscience, 3, 157-163. doi:10.1038/ngeo779.
  8. Kunkel, K.E., and Coauthors, 2008: Observed changes in weather and climate extremes. In Weather and Climate Extremes in a Changing Climate: Regions of Focus: North America, Hawaii, Caribbean, and U.S. Pacific Islands, Synthesis and Assessment Product 3.3 [T.R. Karl, G.A. Meehl, C.D. Miller, S.J. Hassol, A.M. Waple, and M.L. Murray (eds.). U.S. Climate Change Science Program, Washington, DC, pp. 35-80. [Available online at https://downloads.globalchange.gov/sap/sap3-3/sap3-3-final-all.pdf]
  9. Kunkel, K.E, and Coauthors, 2013: Regional Climate Trends and Scenarios for the U.S. National Climate Assessment. Part 2. Climate of the Southeast U.S., NOAA Technical Report NESDIS 142-2, 94 pp. [Available online at http://www.nesdis.noaa.gov/technical_reports/NOAA_NESDIS_Tech_Report_142-2-Climate_of_the_Southeast_U.S.pdf]
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  12. National Weather Service, cited 2017: Extended Period of Heavy Rain and Flooding in Puerto Rico and the U.S. Virgin Islands, May 12–June 16, 2011, http://www.weather.gov/media/sju/hydrology/flood_May12_Jun16.pdf.
  13. National Weather Service, cited 2018: Mean Annual Rainfall 1981-2010, https://www.weather.gov/images/sju/hydrology/2010_ncdc_precip_normals_PR_USVI.jpg.
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  15. NOAA, cited 2018: National Hurricane Center, 2017 Atlantic Hurricane Season, https://www.nhc.noaa.gov/data/tcr/index.php?season=2017&basin=atl.
  16. NOAA Office for Coastal Management, cited 2018: Historical Hurricanes Tracks Tool v4.0, https://coast.noaa.gov/hurricanes/#/search/location/18.220833/-66.590149/200/nmi.
  17. Parris, A., and Coauthors, 2012: Global Sea Level Rise Scenarios for the United States National Climate Assessment. NOAA Technical Report OAR CPO-1, National Oceanic and Atmospheric Administration, Silver Spring, MD, 37 pp. [Available online at http://scenarios.globalchange. gov/sites/default/files/NOAA_SLR_r3_0.pdf]
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