Sweeping off the African coast in thick plumes of tropical moisture, most equatorial storms die quickly in the Atlantic Ocean, little more than windy downpours Sweeping off the African coast in thick plumes of tropical moisture, most equatorial storms die quickly in the Atlantic Ocean, little more than windy downpours. But the hurricane season that begins on June 1 could usher in a far more active pattern.
Experts at the National Weather Service (
NWS) expect that close to a dozen tropical storms will survive to threaten the southeastern and Gulf coasts of the United States. Three or more could become Category-3 hurricanes, defined on the Saffir-Simpson Hurricane Scale as cyclones with maximum sustained winds surpassing 110 miles (175 kilometers) per hour.
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This season, there are more eyes in the skies than ever to monitor and track hurricane formation and development. Helping forecasters to fine-tune their predictive computer models is a varied constellation of 10 key satellites, using an array of 15 different instruments that train sophisticated sensors on the fronts roiling the air and water below.
Boosting this wealth of real-time satellite observations are readings from weather balloons and airplane fly-throughs, plus a powerful new machine: an NWS supercomputer that will eventually run nearly 30 times faster than its predecessor. Add it all up, and coastal dwellers should rest a little easier knowing that theyll likely have plenty of advance warning for the most ferocious blows.
"In the last five years in particular weve taken tremendous strides," said Stephen Lord, director of the Environmental Modeling Center, part of the National Atmospheric and Oceanic Administrations (NOAA) Centers for Environmental Prediction. "Theres no question that over the past decade satellites have improved our forecasting ability. For forecasts longer than two days, were very dependent on satellite data. Its pretty much the only game in town."
Counting on the gear
Hurricane modelers use a variety of satellite-mounted instruments in order to "initialize," or enter into computer models current information on weather systems. Most look directly at and through the atmosphere, measuring such parameters as air temperature, water vapor and precipitation, as well as wind speed and direction. Several examine ocean temperature and ocean height, key elements when assessing the threat of hurricane intensification.
"For forecasts longer than two days, were very dependent on satellite data. Its pretty much the only game in town."
The gear is piggybacked on a variety of platforms, including Department of Defense and civilian, along with national and international dedicated-environmental spacecraft. The F series of satellites in the DODs Defense Meteorological Satellite Program, for example, carry a microwave imager that measures precipitation, wind speed and water vapor. European satellites feature a device known as a scatterometer that collects data on winds and the direction of surface waves on the ocean.
The SeaWinds scatterometer on NASA's QuikSCAT satellite is a specialized microwave radar that measures oceanic near-surface wind speed and direction. A U.S.-French venture, the
TOPEX/Poseidon satellite, uses an altimeter to measure ocean wave height and wind speed, from which researchers infer water temperature and salinity. Other satellites overseen by NOAA use infrared detectors to chart air temperature and moisture."All the instruments essentially provide some measure of atmospheric radiation," Lord said. "We use that information to infer atmospheric temperature and moisture and, in some cases, winds. The more looks we give the atmosphere the better we understand its structure at any given moment. A storms movement depends on atmospheric structure --- wind and temperature."
Lord says that the models have been better at predicting storm track than intensity. In part thats due not so much to lack of sensor coverage or sensitivity, but the ability of models to successfully incorporate ever-increasing amounts of information. Software and hardware upgrades are underway to address those issues. The stakes are high: the current maxim is that coastal evacuation costs a minimum of one million dollars a mile.
GOES a go
Additional hurricane help may come from the newest in the family of Geostationary Operational Environmental Satellites, GOES for short. The successful May 3 launch of GOES 11 brings to three the number of NOAA hurricane-monitoring weather satellites. On May 18, GOES 11 transmitted its first image from 22,300 miles (35, 885 kilometers) out in space.
"The good news is that its working perfectly," said Dennis Chesters, GOES project scientist for NASA Goddard Space Flight Center. "Its the best one weve ever done. GOES 11 is likely to last a long, long time."
Like its GOES 8 and GOES 10 kin already on station monitoring the Atlantic and Pacific oceans respectively, when fully operational this newest addition will beam to Earth pictures of clouds and cloud formation, as well as temperature readings and atmospheric moisture measurements.
For now, the satellite is still undergoing testing and evaluation of critical systems. Should a hurricane develop in the interim, GOES 11 may be placed in rapid-scan mode, transmitting images every five minutes rather than the usual 30. For now, though, forecasters plan to rely on GOES 8 and GOES 10 for day-to-day hurricane monitoring.
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