Taking the Temperature of the Hurricane Pool

Taking the Temperature of the Hurricane Pool

According to the meteorological calendar, hurricane season began on May 15 in the Eastern Pacific Ocean and on June 1 in the Atlantic. But is the ocean ready for the season?

The map above provides at least a partial answer. Shades of violet-blue depict water temperatures below 27.8 degrees Celsius (about 82 degrees Fahrenheit), while shades of pink-red depict waters above that threshold. Scientists generally agree that sea surface temperatures (SSTs) should be above 27.8°C to promote the development and intensification of hurricanes and cyclones. (There are some exceptions.)

As of May 30, 2014, hurricane-ready waters in the Atlantic basin were concentrated in the Caribbean, along the Florida coast, and across the equator between Africa and South America. In the Eastern Pacific, the fuel for hurricanes stretched the length of Central America. Note how the supply of hurricane (cyclone/typhoon) ready waters are much broader and more substantial in the Western Pacific and North Indian ocean basins, where every season is typhoon season.

“Sea surface temperatures are one of the parameters that forecasters use to look at the fuel available for storm intensification,” said Scott Braun, a research meteorologist and leader of NASA’s Hurricane and Severe Storm Sentinel (HS3) campaign. “A more relevant parameter is ocean heat content, which is a measure of not only the warmth of the ocean but the depth of the warm layer. You can have very warm SSTs, but if the warm waters are quite shallow, the hurricane will readily mix colder water to the surface and quickly eliminate the fuel for the storm.”

Ocean heat content is often derived by satellite altimeters such as OSTM/Jason 2, which measures deviations in the height of the ocean surface. The height of the surface reflects heat content because warm water expands to fill more space than cool water. You can see a map of sea surface around the Americas in our recent Image of the Day about El Niño.

The map above was built with data from the Microwave Optimally Interpolated SST product, a NASA-supported effort at Remote Sensing Systems. The research team combines measurements from NASA’s TRMM Microwave Imager (TMI), the U.S. Navy’s WindSAT instrument on the Coriolis satellite, and the AMSR2 instrument on Japan’s GCOM-W. All three sensors observe emissions of microwaves from the sea surface; those measurements capture the temperature of the top few millimeters of the water.

In addition to satellite measurements of ocean conditions, NASA and its research partners are continuing the HS3 airborne mission in 2014. For the third year in a row, scientists from NASA, the National Oceanic and Atmospheric Administration (NOAA), and other federal and university partners will study the genesis and development of hurricanes over the Atlantic Ocean. The backbone of the HS3 campaign is the Global Hawk robotic research plane, which can fly at high altitudes and for as much as 24 hours before refueling. NASA will deploy two Global Hawks this year, with one focusing on the environment around tropical storms and the other flying over the top.

NOAA provides the forecasts and monitoring of tropical weather conditions for the United States, often integrating NASA satellite measurements into other data sets that it relies on. At the same time, NASA pursues hurricanes in the name of research and experimental observations that can further fundamental understanding of the science and improve future models and forecasts.

NASA Earth Observatory image by Jesse Allen, using AMSR2 data from Chelle Gentemann and Frank Wentz, Remote Sensing Systems. Caption by Michael Carlowicz.

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