A Giant Step in Observing Hurricane Winds

The first operational flight of an Air Force Hurricane Hunter plane reporting surface winds from an instrument called the Stepped Frequency Microwave Radiometer (SFMR) occurred on August 1, 2007. The flight occurred in a tropical wave located just east of the Leeward Islands. The SFMR is a state-of-the-art instrument designed to continuously and accurately measure the winds at the ocean’s surface directly below the aircraft. The instrument is installed on the Air Force’s WC-130J within a pod attached to the aircraft’s wing. As the plane flies through a tropical disturbance, a tropical storm or a hurricane, the SFMR senses microwave radiation naturally emitted from foam created on the sea by winds at the surface. Computers then determine wind speeds based on the levels of microwave radiation detected.

The SFMR has been developed under the guidance of the University of Massachusetts Microwave Remote Sensing Laboratory, NOAA’s Hurricane Research Division (HRD), and the private sector company ProSensing. The first experimental SFMR surface wind measurements were made in Hurricane Allen in 1980. NOAA’s two P-3 Hurricane Hunters have had various versions of the SFMR with the first real-time retrieval of winds occurring on board a NOAA plane in Hurricane Earl in 1985 and the first operational transmission of winds to the National Hurricane Center from a NOAA plane occurring during Hurricane Dennis in 1999. The persistence and hard work of research scientists at HRD along with the appropriate staff of the NOAA Aircraft Operations Center and U.S. Air Force Reserve Command are to be commended. Also, in my opinion, the successful development of the SFMR would not have occurred without the financial support from the NOAA Office of the Federal Coordinator for Meteorology.

Three Air Force Hurricane Hunters are currently equipped with the SFMR and an additional plane is scheduled for the upgrade each month until all ten Air Force planes have been outfitted. This is occurring thanks to $10.5M directed by Congress to the Air Force in a Hurricane Supplemental Bill after the 2004 Hurricane Season.

Without the SFMR, surface winds are usually estimated from flight level winds (typically 10,000 feet in a hurricane), estimated from the sea state, estimated from pressure-wind relationships, or measured from dropsondes released from the aircraft. The SFMR directly measures the surface winds and is not confined to a single point like the dropsonde. The constant measurement of surface winds gives the National Hurricane Center a more complete picture of the storm. Having this instrument not only on the two NOAA Hurricane Hunter planes but also eventually having it on all of the Air Force Hurricane Hunters will be a tremendous help to our Nation’s Hurricane Warning Program.

One needs to remember, however, that the SFMR reports “observations” of surface winds. The National Hurricane Center has been very honest in saying that there are limitations in “forecasting” the intensity of hurricanes. Intensity forecasting has been listed by NHC forecasters as the number one priority needing improvement.

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