Rapid Hurricane Intensity Changes

Loop Current spawns '60s style weather phenomenon

VIRGINIA KEY, FL (October 3, 2005) — Not since 1961 have two category 5 hurricanes assailed the same basin in the way that Katrina and Rita made their mark this hurricane season, demonstrating once again, the power of the Gulf of Mexico Loop Current system. A team of researchers has learned a lot from Katrina and Rita as the scientists monitored ocean heat circulation on the surface and at greater depths in the Gulf of Mexico to understand why tropical storms can gain intensity so quickly and ultimately to improve forecasting of these intense land-falling storms

“A positive outcome of a hurricane season like this one is that we've been able to collect a great deal of data that will help us learn more about the Loop Current and associated warm eddies, which are basically a hurricane intensity engine,” said Dr. “Nick” Shay, University of Miami Rosenstiel School of Marine & Atmospheric Science professor of meteorology and physical oceanography. “The last time we had a season with two category 5 hurricanes in the same basin was in 1961 with Carla and Hattie. However, the same phenomenon occurred the year before in 1960 with Donna and Ethel.”

The Loop Current is a horseshoe-shaped feature and flows clockwise, transferring warm subtropical waters from the Caribbean Sea through the Yucatan Straits into the Gulf of Mexico and then back out of the Florida Straits as the Florida Current that forms the core of the Gulf Stream along the eastern seaboard. This year, the Loop Current flows extended deeply into the Gulf of Mexico – approximately 500 kilometers – during hurricane season. The currents at this time of year typically become unsteady and pinch off deep, warm eddies. The warm water then becomes ideal for hurricanes to build up strength as they pass over the ribbon-like Loop Current or any of its eddies.

After Hurricane Katrina and one week before Hurricane Rita, Dr. Shay, Dr. Peter Black from the NOAA Atlantic Oceanographic and Meteorological Laboratory (AOML) Hurricane Research Division, and Eric Uhlhorn from the UM/NOAA Cooperative Institute for Marine and Atmospheric Science deployed Airborne Expendable Conductivity, Temperature, and Depth profilers (AXCTDs); Current Profilers (AXCPs); and Bathythermographs (AXBTs) to obtain information on water temperature to depths of up to 1,000 meters. The AXCTDs and AXCPs, which were funded through the National Science Foundation, are dropped from a NOAA WP-3D aircraft to measure salinity and current.

"Scientists have known that hurricanes form above the world's warmest ocean surface waters," said Jay Fein, program director in the National Science Foundation (NSF)'s division of atmospheric sciences. "This study adds new information about hurricanes' journey to landfall and will help to better predict their path and intensity changes during their final hours over open water."

Additionally, just two days before Rita, Dr Black, in collaboration with Dr Peter Niiler of the Scripps Institution for Oceanography and Dr. Rick Lumpkin of AOML, deployed 20 surface drifters that measure surface and subsurface thermal conditions while traveling clockwise around a Loop Current warm eddy lying in the path of Rita just south of Louisiana. This deployment, supported by Scripps and NOAA, was conducted in collaboration with the Air Force Reserve Command from a C-130J aircraft flown by the 53rd Weather Reconnaissance Squadron, whose base in Biloxi, Miss., was badly damaged by Katrina. This effort was an outgrowth of an Office of Naval Research-supported CBLAST experiment conducted with NOAA during the past two years, which demonstrated the utility of using drifters and floats to sample the upper ocean and air-sea interface during a hurricane.

“We are learning a great deal this year, as these storms pass over the deep, warm waters of the Loop Current,” Dr. Shay said. “We have long known that these systems of ocean circulation are a very important way for the ocean to distribute heat and energy, but until now, we just didn't have much data on the role they played in building extreme hurricane intensity.”

Consequently, scientists now have data sets that are part of a comprehensive ocean sampling program, which will be critical to develop and evaluate the new NOAA coupled hurricane-modeling system (HWRF) being developed at the National Centers for Environmental Prediction and to evaluate algorithms for intensity prediction at the National Hurricane Center/Tropical Prediction Center.

“This represents one of the most comprehensive ocean data sets where two major hurricanes passed through the same region,” said Dr. Frank Marks, director of hurricane research at AOML. “In many ways, these series of observations are a testament to how new ocean observations are helping us understand hurricane intensity change better.”

Hurricanes Katrina and Rita have a lot in common with Hurricane Opal, which happened 10 years ago on Oct. 4, 1995. This was when meteorologists first recognized the pivotal role the deep, warm eddies play in quickly building hurricane intensity. Opal encountered a warm water eddy in the Gulf of Mexico and strengthened in intensity from category 1 to category 4 in just 14 hours.

Rosenstiel School is part of the University of Miami and, since its founding in the 1940s, has grown into one of the world's premier marine and atmospheric research institutions.

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Media Contacts

UM Rosenstiel School
Ivy Kupec or Annie Reisewitz
(305) 421-4704/ (305) 824-1601
Scripps Institution of Oceanography
Mario Aguilera or Cindy Clark
(858) 534-3624
Natl. Oceanic & Atmospheric Administration
Jana Goldman or Erica Rule
(301) 713-2483, ext. 181/ (305) 361-4541
National Science Foundation
Cheryl Dybas
(703) 292-7734
Office of Naval Research
Ms. Jennifer Huergo
(703) 696-0950