Hurricane Andrew’s wind field
A scientist reflects on Hurricane Andrew
Monday, August 27, 2012
Just tell me if Andrew’s coming
On Saturday, August 22nd 1992, I was meeting with Herb Saffir (coauthor of the Saffir Simpson Scale) in his Coral Gables office on a manual for post-storm damage investigation as the hurricane scientist member of a panel Herb was chairing for the American Society of Civil Engineers. As the meeting ended it became apparent that Andrew, which had become a hurricane that morning, was approaching the Bahamas and was not going to recurve northward as hoped. It was coming right at us! I called my wife and told her to get to Publix since a hurricane warning was imminent and we knew from earlier storms that there would soon be a run on supplies. I headed off to Home Depot for plywood and wondered how I would protect the house and still make my scheduled research reconnaissance flight into the storm Sunday on one of NOAA’s P3 Hurricane Hunter aircraft. As a hurricane wind specialist I would be monitoring the wind field and radar displays over a proposed ten hour mission. That mission was scrubbed when it became apparent that the aircraft would need to be evacuated from their base at Miami International Airport. Instead, the Air Force Reserve’s of the 53rd Weather Squadron out of Keesler Air Force Base in Biloxi flew a C-130 into the storm late Sunday, while I thankfully completed my shutters and we accommodated some friends (and their pets) who lived in a storm surge evacuation zone. Our home was near 20 ft above sea level on the coastal ridge in Coconut Grove (about 3 miles south of downtown Miami) so flooding would not be a problem.
Well, Andrew hit overnight and by 9 am Monday morning and we seemed to be OK. Lots of trees were down and the power out but the house was intact with just a few broken roof tiles and one cracked window. We walked down to Biscayne Bay to check on the flooding and took some pictures, feeling the excitement of viewing a dramatically changed landscape. The mood changed when we received a call from another friend who was crying and upset about damage further south. We spent hours picking our way about 10 miles south to find that our guests home in “Whispering Pines” was within ground zero of the northern eyewall of Andrew. Their roof covering was peeled, double front doors were blown in, and all their living room furniture had been blasted through a sliding glass door into their pool. Our friends were in shock and time was short due to an impending curfew so we made our way to Dixie Highway (difficult since all the street signs were blown down) for the drive back to Coconut Grove. We were marveling at the lack of any organized response, when we noticed a white school bus making its way southward on US1. We all cried when we saw that the first responders were the City of Charleston Police Department. This was pay back from 1989, when Charleston was hit by Hurricane Hugo and Metro-Dade County helped in the response.
Overnight more than 200,000 were left homeless without power and with few supplies. Fifteen died from blunt trauma or drowning in the storm surge. It took days for significant relief to arrive with Kate Hale, the Dade emergency Director pleading “Where the hell is the cavalry on this one?” Despite the slow pace of response, it was amazing how the communities of South Florida pulled together to help each other out, with neighbors helping each other and sharing supplies.
It was also amazing that the Air Force crew on that C130 flew all night, monitoring Andrew as it strengthened through landfall and continuing to fly a hazardous pattern over land as the storm progressed inland. For several months afterwards our lab worked to piece together data and reconstruct Andrew’s wind field. We visited sites with incredible damage where lives were lost. The public sent data in and we worked with wind engineering colleagues who wind tunnel tested anemometers similar to the one that measured the peak wind speed in Perrine. State Attorney General Janet Reno called to check on how strong the winds were to allay some of the rumors. Back then the reconnaissance aircraft did not have a way to measure the winds near the surface so storm intensity was estimated as a fraction of the maximum flight-level winds, resulting in a Category 4 assessment on the Saffir-Simpson scale. After 10 years, a new type of instrument, the GPS dropwindsonde, could provide measurements closer to the surface suggesting that Andrew may have been a Category 5 storm at landfall. Our recent research on the Stepped-Frequency Microwave radiometer, a new instrument that remotely senses wind speed from the radiative emission of sea foam, reinforced the Category 5 assessment.
Hurricane Andrew had a profound affect on everyone living in South Florida at the time. Its one of those life milestones from which we measure everything before or after. Miami-Dade county responded with a tough new building code with product testing and enforcement, which influenced the eventual development of a unified Florida Building Code. The insurance industry started to use sophisticated models that could estimate the risk of future Andrews, and performance in emergency management and response was found to influence presidential elections. The rebuilding created an economic boom, but many folks moved away while others moved in transforming rural areas like Homestead from farm fields into suburbs.
We developed a research analysis system called H*Wind, which now allows us to monitor and analyze the wind field in real time using every piece of data we can get our hands on, including portable MET towers placed just ahead of the storm by engineering and atmospheric science students and faculty at the University of Florida and Texas Tech. We have a much better idea of the intensity and extent of the damaging winds now, and also developed new damage scales based on integrated kinetic energy that consider the destructive potential of large storms.
Thankfully Florida’s big bend has not experienced any Andrew’s but many will remember the power outages and downed trees from late season Hurricane Kate in 1985. As I write this, Tropical Storm Isaac is entering the Caribbean Sea and some of the global scale prediction models suggest Florida, perhaps even the Big Bend, will be threatened next week. Its too early to trust these predictions just yet, but its not too early to reflect on Andrew and Kate, and other hurricanes that have affected our state and country.
Andrew occurred during a year forecast to have “below normal” activity. I’m often asked, “What kind of year are we going to have”?
My answer: It doesn’t matter... just tell me whether Andrew’s coming.
Mark Powell is an atmospheric scientist for the National Oceanic and Atmospheric Administration’s Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. He is a fellow of the American Meteorological Society, and a Certified Consulting Meteorologist. Mark is stationed at Florida State University’s Center for Ocean-Atmospheric Prediction Studies. This piece represents his opinion as a scientist and does not represent an official position of NOAA.
References:
For more research by Mark go to:
http://www.aoml.noaa.gov/hrd/Powell/
As a scientist with NOAA’s Hurricane Research Division, I contributed to papers See below) on Hurricane Andrew’s wind field and additional research on how to best estimate surface winds in hurricanes.
Tree limb debris along Tigertail and Swanson in Coconut Grove looking east toward 22nd avenue
Storm surge debris runup on east end of 22nd Avenue and Bayshore Drive looking east towards Biscayne Bay
Storm surge slowly receding on Bayshore Drive looking north about 9 am, August 24th, 1992
Hurricane Andrew in Coconut Grove
(All photos by Mark Powell, ~ 9 am on August 24th)
Winds at Coconut Grove are estimated to have been over 100 mph but well below the over 150 mph peak winds that struck the Perrine/Cutler Ridge area that bore Andrew’s northern eyewall
Storm surge pushed westward up the coastal ridge. Photo looking west at Bayshore Drive and 27th Avenue.
Hurricane Andrew at Naranja Lakes
(All photos by Mark Powell)
Several deaths occurred in this development. According to engineering studies, complete roofs (with tie beams attached, became airborne and impacted buildings downwind. Note tie beam on ground in foreground.
This area was struck by 120-140 mph winds coupled with a 180 degree wind direction change that contributed to the damage.
The flat nature of the roofs and lack of a load path to the foundation allowed strong winds to generate enough lift so the roofs turned into large “airplane wings” that took-off downstream
Noted wind engineer Dr. Peter Vickery and fellow atmospheric scientist Dr. Peter Black (r) examine damage at Naranja Lakes.
This location suffered from a non-robust weather station installation. The plumbing conduit unscrewed itself during the strong winds, turning the anemometer upside down and eventually the heavy brass F420 instrument worked its way off its pedestal. Finally, the tower was hit by some debris and a guy wire pulled out, causing the mast to fall over. These issues (and others) led us to question reports that winds at this location were “pegged” for a long time period. For more info see Powell et al., 1996.
Hurricane Andrew’s damage to the Tamiami Airport Anemometer
(All photos by Mark Powell)
