When we first published this article (September 10, 2013), Humberto was still a tropical storm near the Cape Verde Islands. The forecast showed it was en route to become the first Atlantic hurricane of the 2013 season, and it did. However, its status as a hurricane is still likely to be very brief, on the order of 48 hours.
A look at the oceanic sea surface temperatures (Fig. 1) retrieved by NASA’s Atmospheric Infrared Sounder (AIRS) in Near-Real Time, along with the projected hurricane track (+ symbols), makes it clear Humberto is heading in the “wrong” direction. Humberto will have its chance, though, to intensify and become a Category 1 hurricane during September 11-12, during his turning north. However, this turn will mean a rapid doom for the storm, bringing it over a tongue of cooler waters off the west coast of Africa.
Studies have determined that (among many other things) hurricanes require substantial storage of heat in the oceanic surface layer, which can be very approximately manifested as persistent ocean surface temperatures of about 27 degrees Celsius (300 Kelvin). Although approximate, it is a simple and good indicator of sufficient energy supply for a tropical depression to grow into a hurricane and maintain its strength. This temperature is placed in the middle of the color bar temperature scale for Figure 1. Thus, the boundary between the reddish and bluish hues in the image roughly distinguishes the areas that would facilitate hurricane development from those that would suppress it.
Note the hot average daily land surface temperatures observed by AIRS over Africa – the breeding grounds for tropical “waves”. They appear as areas of low atmospheric surface pressure with moderate cyclonic rotation, propagating west into the tropical Atlantic. At the same time, autumn cool is steadily advancing in Canada.
Barring drastic changes in the current state of the tropical Atlantic, the next tropical wave or depression that takes a more southern route will have improved chances to develop into a more powerful hurricane. September and October are the peak months for the occurrence of Atlantic hurricanes.
Figure 1. Sea surface skin temperatures (TSurfStd) retrieved by AIRS, an instrument on NASA’s Aqua satellite. The image depicts a two-day average for September 8-9, 2013, derived from the Near-Real-Time retrieval. Symbols (+) show the current location and predicted track of Humberto. The color bar temperature scale ranges from blue to yellow/red, transitioning at a temperature of approximately 27 C (300 K), the temperature basically required for hurricane formation and maintenance. (Click on the image to view it full-size.) White colors indicate areas with persistent cloudiness that did not allow observations of surface temperatures.
“AIRS is managed by NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif., under contract to NASA. JPL is a division of the California Institute of Technology in Pasadena.”
AIRS near-real time data is available from LANCE (Land Atmosphere Near real-time Capability for EOS).
Get AIRS data from the GES DISC with Mirador: http://mirador.gsfc.nasa.gov/
Plot AIRS data with Giovanni: http://giovanni.gsfc.nasa.gov
Questions or comments? Email the NASA GES DISC Help Desk: email@example.com