Hurricane Dennis Yields More than Longevity, NOAA Hurricane Scientists Say

by National Hurricane Center

HURRICANE DENNIS YIELDS MORE THAN LONGEVITY, NOAA HURRICANE SCIENTISTS SAY

September 3, 1999 — Hurricane Dennis might be the storm that just won't go away, but it has proven to be a fertile testing ground for new measurement technology. The result? Improved observations and forecasts of sea-level winds in hurricanes, say NOAA hurricane forecasters.

NOAA's Hurricane Research Division (HRD) and Aircraft Operations Center successfully transmitted sea-level wind measurements on Aug. 29 from Hurricane Dennis, using an experimental instrument aboard NOAA's P3 "hurricane hunter" aircraft.

The measurements were incorporated into HRD's real-time hurricane wind analysis system, combined with conventional winds from buoys, ships, Global Positioning System drop windsondes, and satellite cloud tracking to determine the storm's wind field. Forecasters at the National Hurricane Center then used the wind field as guidance to distribute warnings of gale force winds (40 mph or higher) over coastal North and South Carolina.

"What this new set of data provides is continuous measurement of wind speed over a large area," says NOAA hurricane wind field expert Mark Powell. "Based on successful comparison to the observations such as buoys and coastal weather stations, the data from the new instrument was accepted by the HRD analysis system, in real-time and used by the National Hurricane Center."

The technology in this experiment features a stepped frequency microwave radiometer (SFMR), a sensor built by the University of Massachusetts and Quadrant Engineering in Amherst, Mass., which is currently flown aboard a NOAA hurricane hunter aircraft. The SFMR measures the signal returned by the ocean surface beneath the aircraft as it is churned up by hurricane winds. This technology has been in use for research purposes for a number of years, but has never been available in real-time for forecasting.

The measurements from the SFMR provide a critical addition to existing tools for wind speed measurements, said Powell. Dropwindsondes deployed from aircraft flying through and around a hurricane have been instrumental in providing point observations within a storm, sending information every half second.

Winds measured at flight level (about 10,000 ft.) by the U.S. Air Force and NOAA hurricane reconnaissance aircraft are used in atmospheric models to estimate surface winds. Estimating wind speeds from that altitude have resulted in as much as 20 percent uncertainty. By incorporating the SFMR wind speeds, scientists hope to reduce that uncertainty to provide more accurate forecasts for coastal communities.

"The SFMR gives us much more complete storm coverage at the surface than the sondes, and at a fraction of the cost," said Peter Black, the HRD scientist who helped develop the SFMR. "Eventually, we hope to see this instrument on all hurricane hunter aircraft."

The Hurricane Research Division is located at the Atlantic Oceanographic and Meteorological Laboratory in Miami, Fla. It is one of NOAA's 12 environmental research laboratories across the nation.

NOAA's mission is to predict and describe changes in the Earth's environment and to conserve and manage wisely the nation's coastal and marine resources.

For more information visit the following Web sites:

NOAA's Hurricane Research Division

NOAA's National Hurricane Center

NOAA's Aircraft Operations Center