The 2012 hurricane season in North and Central America arrives
with a muddled outlook. Sea surface temperatures are not particularly warm or
cool, and the El Nino–Southern Oscillation (ENSO) is drifting in a neutral state that
NASA climate scientist Bill Patzert playfully calls “La Nada.”
The map above shows sea surface temperatures (SSTs) in the
tropical Atlantic Ocean and tropical eastern Pacific on May 30, 2012. The map
was built with data from the Microwave Optimally Interpolated SST product, a
NASA-supported effort at Remote Sensing Systems. Researchers
combine observations and analyses from NASA’s Tropical Rainfall Measurement
Mission and Aqua and Terra satellites, as well as the U.S. Navy’s WindSAT instrument on the Coriolis satellite (operated jointly with the Air Force).
Shades of blue depict water temperatures below 27.8 degrees
Celsius (about 82 degrees Fahrenheit), while yellows, oranges, and reds depicts
waters above that threshold. Scientists generally agree that waters above that
temperature are needed to build and sustain hurricanes, though there are exceptions. Of course, measurements of sea
surface temperature account for only the top few millimeters of the ocean, and
the amount of heat stored at greater depths (which is harder to measure) can
also be a factor in hurricane development. So SSTs do not tell the whole story,
but they are a fair predictor of the readiness of the ocean to sustain tropical
storms.
“The waters look on the slightly cool side across some of the
‘main development region (MDR)’—the tropical band extending over the east and
central Atlantic off Africa,” noted Jeff Halvorson, a hurricane researcher at
the University of Maryland–Baltimore County. “Whether this will persist for
several months as we get into the high season, I don't know.”
The official start of hurricane season is June 1, though four
named tropical storms in May—Alberto and Beryl in the Atlantic, Aletta and Bud
in the Pacific—didn't wait for the calendar. The Hurricane Research Division of
the National Oceanic and Atmospheric Administration (NOAA) announced on May 24,
2012, that it is expecting a near-normal season, with nine to fifteen named
storms and four to eight hurricanes. According to NOAA, an average season
between 1980 to 2010 produced 12 named storms with six hurricanes, including
three major hurricanes.
“We shouldn't be fooled by the storms that have already
developed off the southeast U.S. in May,” Halvorson said. “Development can and
does happen this early—albeit infrequently—and these developments are almost
always not far off the U.S. mainland. They have little to do with what is
coming off Africa and streaming across the MDR. So these early home-grown storms
are not necessarily a predictor of the August to October season, which is
dominated by Cape Verde storms.”
Meteorologists often look to ENSO for a sense of whether
atmospheric weather patterns will promote or tamp down hurricane formation. In
general, researchers believe that El Nino reduces hurricane activity and La
Nina promotes it. But the science on the matter is not really settled, and it
may be that ENSO affects the number but not necessarily the intensity of
storms.
La Nina just ended earlier this spring, and the next El Nino may
be some months off. “The equatorial Pacific is neutral, with no El Nino
developing...not even a hint,” said Patzert, who is based at the Jet Propulsion
Laboratory. “If El Nino builds, I think it will be late and whimpy.”
In the eastern Pacific, NOAA is calling for a near-normal or
below-normal season. “Forecasters estimate a 70 percent chance of 12 to 18
named storms, which includes 5 to 9 hurricanes.”
Regardless of the predictions, the key to hurricane season is
vigilance. “The important issue is hurricane preparedness along the coasts,”
said Patzert. “All it takes is one in your neighborhood to wreak havoc. Listen
to the National Hurricane Center, know your evacuation routes, and be super
prepared.”
1. References
NASA Earth Observatory image by Jesse Allen, using WindSat and
MODIS data from Chelle Gentemann and Frank Wentz, Remote Sensing Systems.
Caption by Michael Carlowicz.
Instrument:
Coriolis
- WindSat