USWRPUS Weather Research Program (USWRP)NOAA

The 1999 Hurricane Field Program is the second year of a renewed effort to unravel the mysteries of these devastating storms under a multi-agency (DoD, NASA, NOAA, and NSF) effort over the next 5-6 years, the U.S. Weather Research Program (USWRP). USWRP is focused on the meteorological research community's contribution to the reduction in the impacts of disastrous weather on the nation, in particular hurricane landfall. An important national priority under the USWRP is to improve the forecasts of surface wind intensity, structure and storm surge in landfalling hurricanes in order to mitigate problems associated with these storms. A major source of difficulty in the past has been the inability to measure surface winds directly, and our inability to predict how it changes in response to external and internal forcing.

Several dramatic cases occurred in recent years suggesting a strong role of air-sea interaction processes on hurricane intensity change. Many of these cases occurred within 24 h of landfall where intensity change forecasts are especially critical. In 1992 Hurricane Andrew gained strength as it passed over the Gulf Stream just before landfall in South Florida. While in 1995 Hurricane Opal intensified rapidly as it moved over a warm eddy in the Gulf of Mexico, then rapidly weakened as it moved over colder shelf water. Over half of the 32 storms that occurred in 1995 and 1996 had significant intensity changes when crossing sea surface temperature (SST) boundaries, either preexisting or created by previous storms.

This season we will focus on the relationship between hurricane intensity change and changes in the underlying SST caused by the storm winds. In particular, storm interactions with 3 types of ocean features will be examined:

  1. permanent features, such as the Gulf Stream and Loop Current;
  2. semi-permanent features, such as Gulf of Mexico Warm Eddies; and
  3. transitory features, such as cold wakes from previous storms.

Direct linkages between hurricane intensity change and observed air-sea changes have been difficult to make since many storms are influenced by atmospheric circulations. In addition, detailed oceanographic and atmospheric observations are generally lacking. Thus, the primary goal of this study is to establish the link between changes in air-sea interaction processes brought about by changes in oceanic features and changes in the storm surface winds. To overcome these past difficulties, a mobile observing strategy comprised of air-deployed surface and subsurface probes and airborne remote sensors directly measuring the surface winds.

These experiments seek to measure the surface wind field and upper ocean structure using NOAA WP-3D aircraft flights during 4 time periods:

  1. Early Season (1-4 weeks before storm): One WP-3D aircraft will map the upper ocean structure in a predetermined ocean feature using airborne expendable bathythermographs (AXBT), current probes (AXCP), and conductivity, temperature, and depth (AXCTD) probes.
  2. Pre-Storm: One WP-3D aircraft will map the upper ocean features undisturbed structure with AXBT/AXCP/AXCTD probes 36-48 h prior interaction with the storm, and should be coordinated with a G-IV surveillance mission.
  3. Near-Storm: Two WP-3D aircraft, one following the other, will map the upper ocean structure with AXBT/AXCP/AXCTD probes while the storm is interacting with the ocean feature, and should be coordinated with a G-IV surveillance mission.
  4. Post-Storm: The final phase of this experiment requires a single WP-3D to survey the ocean features structure using expendable probes 24 h after storm interaction.


©1999 NOAA/AOML Hurricane Research Division
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For information about NOAA Hurricane Field Program marks@aoml.noaa.gov
For information about USWRP gall@ncar.ucar.edu, or elsberry@osprey.met.nps.navy.mil
Updated Monday, 28 June 1999made with Mac