Sea Surface Temperature

Sea surface temperature (SST) is an important factor in hurricane dynamics. SST is measured over large portions of the ocean by satellites.

World Sea Surface Temperature graph (SST)at 50km resolution. The image is from July 7, 2009. Daily SST images can be found at: http://www.osdpd.noaa.gov/ml/ocean/sst/sst_anal_fields.html Figure from NOAA.

Sea surface temperatures are generally warmer at low latitudes and colder at high latitudes but SST will vary with the seasons and with surface ocean currents. For forecasting hurricanes, more detailed maps of SST are produced for areas of hurricane formation.

Scientists used more refined data that is a blend of the satellite and in-situ instrument data to produce the high-resolution SST analysis, such as the Reynolds analysis image below.

The image shows color contours of the sea surface temperature Reynolds analysis on July 12, 2009. Note the sharp jump in color contrast at 5 degree Celsius increments in contrast to the gentle gradient of the world SST image above. The sharp jump helps highlight areas of higher temperature such as the particularly warm spots in the Gulf of Mexico. Figure from NOAA-NHC

For hurricane forecasting, it can also be very useful to look at the SST anomalies. A SST anomaly is the difference in the current SST measurement from the long-term average temperature for a given month, in a given place (the climatology). Positive temperature anomalies indicate that the water is warmer than usual and negative anomalies indicate that the water is cooler than usual.

The figure shows the temperature anomalies in the North Atlantic, Caribbean Sea and Gulf of Mexico for July 4, 2009. The temperature anomaly is the difference between the temperature measured and the climatology. Figure from NOAA-NHC.

The vertical temperature distribution in the ocean is also important for understanding hurricane dynamics. While satellites can measure the surface ocean temperature over large areas rapidly and repeatedly, measuring the temperature through the water column requires a fixed buoy with instruments or a ship that can deploy instruments in a specific area. There are also instruments that can be deployed from a plane. The temperature profile through the water column is variable and will change seasonally, as the mixed-layer changes, and as storms pass over.

The warm water is present at much deeper depths in the Caribbean Sea than in the Gulf of Mexico.