NOAA Magazine | NOAA Home Page NOAA's COASTAL WATER TEMPERATURE GUIDE May 3, 2002 — To make your next trip to the shore truly a "day at the beach," find out what to expect before you leave home. Although land and air temperatures vary dramatically within a day, water temperatures are much more stable. Therefore, average water temperatures can give you a pretty good idea of what to expect at the beach weeks (or even months) into the future, thus making it easier to plan beach activities (such as swimming and fishing). NOAA's National Ocean Data Center's Coastal Water Temperature Guide (CWTG) provides both present temperatures and climatological averages in degrees Fahrenheit. Current temperatures are based on real time observations from NOAA's National Ocean Service tide stations and NOAA's National Data Buoy Center buoys. Climatological average water temperatures, on the other hand, are computed using the same data sources, but are instead based on averages of long-period records—ranging from several years to several decades, depending on how long observations have been taken at a given station. The coastal water temperature data provided on the Coastal Water Temperature Guide Web page is broken down into the following 12 regional areas: Northern Atlantic Coast Central Atlantic Coast Southern Atlantic Coast Other Atlantic Sites Eastern Gulf of Mexico Coast Western Gulf of Mexico Coast Northern Pacific Coast Central Pacific Coast Southern Pacific Coast Hawaiian Island Coast Alaska Coast Other Pacific Islands Users can select region-specific water temperature data by either clicking the desired region on the map or text list, which then links you directly to a table containing both present temperatures and monthly climatological averages for the year by location within the selected region. By double clicking on the "Present Temperatures" hyperlink (within the table) you can obtain even more detailed information about the location site, as well as time series plots of the last few hours of NOS Water Temperature data for that tide station—along with other relevant data—or go to the NDBC Buoy Page for the location. Because water temperatures vary more along the Atlantic and Pacific coasts of the United States, these stations are further broken down into two-week averages from April through October. For the Gulf coast, however, water temperatures are more homogenous and, therefore, are reported only as monthly water temperature averages. These temperature tables (except Hawaii, Alaska, and Pacific Islands table) were originally created in the early 1980s by former NODC meteorologist Richard M. DeAngelis. Hawaii, Alaska and Pacific Islands table values are based on NOS publication "Surface Water Temperature and Density, Pacific Coast, North and South America & Pacific Ocean Islands." The CWTG was created by Mr. Don Collins and maintained by Dr. L. Charles Sun and Ms. Debria Hayes. Much of the appeal of coastal areas during the hot summer months are the cool water temperatures... but have you ever wondered why coastal waters are cooler than the surrounding air and land? Basically, due to differences in the physical nature of each media, land and air temperatures warm up and cool down more readily than water. On a large scale, tropical oceans hold tremendous amounts of heat, while polar waters can be frigid year-round. Land and the air above it, on the other hand, quickly warm and cool off with the seasons. You can test this concept on your own by going to the beach barefoot on a hot sunny day in the middle of the afternoon. The air is warm and the sand is almost too hot to walk on, although the water is refreshingly cool. If you go back at midnight (especially on a clear night), however, air and sand are chilly, while the water temperature has remained relatively constant. Other interesting coastal water temperature facts and figures include the following: Over half the heat that reaches the Earth from the sun is absorbed by the ocean's surface layer. Therefore, currents originating near the equator are warm, while currents that flow from the poles are cold. Can water temperatures differ between near-shore and offshore sites at the same latitude? Why or Why Not? Yes, several factors can influence the sea surface temperatures along near shore waters more so than offshore waters. These factors include river runoff, higher cooling and heating rates, continental air masses, near-shore ocean currents, and upwelling effects. On the West Coast, for example, near-shore waters are often much colder than offshore waters (at the same latitude) due to upwelling. Upwelling is the movement of cold water from deeper depths to the top of the ocean. Along the coasts of Washington, Oregon, and California, coastal winds effectively transport surface waters offshore. Therefore, seawater must rise from the depths to replenish the water that is being pushed away from the coast. These cooler, nutrient-rich waters rise from depths of 50-300 meters to the surface of the ocean. Therefore, waters just along the coast are usually several degrees cooler than the waters offshore. Are air temperatures the same over land and water? Because it takes far more energy to change the temperature of water compared to land or air, water warms up and cools off much more slowly than these other media. As a result, inland climates are subject to more extreme temperature ranges than coastal climates, which are insulated by nearby water. Relevant Web Sites NODC Coastal Water Temperature Guide National Ocean Service tide stations National Data Buoy Center Real-Time Bouy Data BIOLOGY AND LIFE SCIENCES: NODC Costal Water and Temperature Guide Media Contact: Patricia Viets, NOAA Satellite Service, (301) 457-5005