The Atlantic’s Great Tropical Cyclones – cont’d
by: Eric Brown
21st Century
“The storm is master. Man, as a ball, is tossed twixt winds and billows.”
Friedrich von Schiller – William Tell
Tropical Storm Allison, June 2001 – One of the worst misconceptions about tropical cyclones is that only the strong ones are deadly and destructive. Wind, however, isn’t the hurricane’s greatest killer…it’s water. And as the previous two entries demonstrated, it often isn’t the water from the sea that you should worry about, it’s the water that falls from the sky. In November, 1991, Tropical Storm Thelma drowned the Philippines in an astonishing 20 inches of rain in just three hours. This was one of the highest rainfall rates ever recorded and it unleashed devastating flash floods that wiped out entire villages. It’s believed that at least 7,000 people died with possibly over 1,000 more unaccounted for. Nearly 5,000 of those were in the city of Ormoc alone. Of all the incredible, devastating typhoons that have ravaged the Philippines over the years, this puny little tropical storm that never had winds stronger than 50 mph was the deadliest (at least until epic Typhoon Haiyan killed 7,400 in 2013). Ten years later, this painful lesson would be brought a little closer to home.
Houston, Texas is the fourth largest city in the United States, home to 1.9 million people at the turn of the millennium. It sits in a flat, marshy coastal plain, laced by rivers and bayous much like New Orleans. The city’s average elevation is only about 50 feet above sea level, with many areas lower than that and a very high water table. However, before Allison, few tropical systems had exploited this geography. In 1837, a hurricane known as Racer’s Storm reportedly caused up to four feet of flooding in downtown Houston. The historic Galveston hurricane in 1900 caused minimal damage in Houston, as did the 1915 hurricane. In 1983, Hurricane Alicia blasted downtown with wind gusts approaching 100mph, blowing out numerous skyscraper windows. However flooding was minimal and mainly confined to eastern suburbs. No one realized just how vulnerable the city was.
After World War II, the city’s population exploded. Home to less than 400,000 before the war, by 1970 Houston was home to 1.2 million. As the city grew, so did its need for land and resources. Marshy, wetland areas were reclaimed to build new subdivisions and dredging of the city’s rivers and bayous lowered the land’s elevation. It was a recipe for disaster.
Allison’s origins can be traced back to a tropical wave that left the coast of Africa on May 21, very early for an African wave. It traveled all the way across the Atlantic nearly devoid of thunderstorms, moving inland over northern Venezuela before crossing into the Pacific. Threat, gone…or so it was thought. On June 2, it stalled off the south coast of Mexico and developed a strong circulation, however strong wind shear prevented any development and the wave moved north, inland over Mexico. The wave disappeared, however the strong mid-level circulation remained and emerged over the Gulf of Mexico on June 4. Ripe conditions triggered strong thunderstorms and a disturbance developed beneath the strong mid-level circulation. It wasn’t long before a low-level center redeveloped and Allison was born.
This is when things got complicated. A low pressure system high in the atmosphere over south Texas southwest of Allison interacted with the storm’s circulation and helped fuel the explosion of thunderstorms around the center. It also helped Allison greatly broaden its wind field. Within hours of its official formation, tropical storm force winds (>40 mph) extended out up to 230 miles from its center and the storm itself, despite tepid water temperatures, had intensified with 60 mph sustained winds. Now the real question remained…where was it going?
Trapped beneath a large high pressure system over the southeast, Allison initially wasn’t going anywhere. Model forecasts were all over the place. Some took the storm west into southern Texas and northern Mexico. Others took the storm east into Louisiana. Instead, helped in part by the push from the upper low to the south, Allison drifted north toward east Texas. The storm actually weakened before making landfall, due in large part to cooler water near the coastline. However, it’s what happened after landfall that changed everything.
Once inland, Allison quickly weakened to a tropical depression. Now it had moved away from the influence of the upper low that had been helping it drift north and ran into a wall of high pressure. The storm came to a dead stop right over the Houston metro and all their bayous. Making matters worse, the circulation was so large that it was able to tap into the warm waters of the Gulf of Mexico, funneling a terrific deluge of rain into the Texas coast.
Parts of the Houston metro received over two feet of rain in 12 hours. Rainfall rates as high as six inches per hour were recorded as the storm parked over the city. The effect was catastrophic. Five of the six bayous in the city burst their banks. Four of them reached the highest water levels in over a century of record keeping. By the morning of June 9th, downtown and sprawling neighborhoods north of Interstate 610 were inundated. Despite the worst of the flooding miraculously missing Friday rush hour the previous afternoon, thousands of vehicles were stranded on the city’s freeways, which were under several feet of water in places. Hundreds of drivers were rescued by helicopter or were forced to seek higher ground on foot. Thousands more had to be airlifted off of rooftops as homes flooded into the upper floors.
The sprawling complex of hospitals that make up the Texas Medical Center, the largest complex of its kind in the world, was also inundated. Multiple hospitals lost all power, including backup generators, and were forced to evacuate thousands of patients, many of them in critical condition, down dark stairwells in sweltering 100+ degree heat. Patients who could not breathe on their own had to be manually ventilated for hours before they could be airlifted to other hospitals by Coast Guard and National Guard helicopters. Miraculously, no patients died during the evacuation. Multiple medical science centers lost decades of priceless research, including the life’s work of many scientists. All three major universities in the city also suffered significant flooding, none more so than the University of Houston, whose law library lost 174,000 books.
The flooding was arguably exacerbated by Houston’s system of underground tunnels that connect many of the city’s buildings downtown. Floodwaters spilled into the tunnels and inundated the basements of numerous buildings. This included parts of the upscale theater district, shopping centers, government buildings, underground parking garages, and several high rise office towers.
After spending about two days parked over Houston, Allison began a slow drift back to the south as two competing high pressure systems to the northwest and northeast battled for dominance. Finally, Allison emerged back over the Gulf of Mexico on June 10. The high pressures had begun to weaken and an upper level trough to the south began to move the storm east-northeast toward Louisiana. As it interacted with the trough, its circulation expanded even more and began to take on the characteristics of a non-tropical low pressure system, becoming something of a hybrid.
Allison made landfall over the Louisiana bayous, unleashing another deluge of rain. Parts of Louisiana got nearly 30 inches of rain. Luckily this was over much more sparsely populated areas. As it was, over 1,000 homes were flooded in St. Tammany Parish alone. And so Allison began its weeklong march across the southeast that everyone pretty much forgot about. The storm dropped over ten inches of rain on nine states, causing widespread flooding in all of them. Extensive river flooding struck Pennsylvania, where over 200 homes were destroyed and numerous roads and bridges were washed out. Flooding occurred as far away as New England. Finally, on June 17, Allison moved off the New England coast and became extratropical.
The devastation in Houston was incredible. Over 73,000 homes were flooded, nearly 3,000 of which were total losses, and 300,000 people were left homeless. Also, roughly 95,000 vehicles were flooded. Hospitals at the Texas Medical Center were shut down for over a month. A temporary hospital with 88 doctors was ultimately set up to compensate for the loss of medical service for the city. 22 people died in the Houston area, most of them in cars that became trapped in floodwaters. Miraculously, none of the deaths occurred in homes. This is likely due to the worst of the flooding happening in daylight. Damage in Houston alone came to $5.2 billion. Overall, Allison killed 41 people, making it the deadliest storm in US history that never became a hurricane. Eight people died in Florida and seven died in Pennsylvania, evidence of the far reaching effects of the storm. Damage came to $8.5 billion.
In the wake of Allison, however, little was done to beef up the city’s flood control systems. The Harris County Flood Control district actually saw funding cuts that caused some improvement projects to be shelved entirely. Allison was seen as Houston’s “perfect storm.” Few with actual authority to make decisions seemed to think it could ever happen again. Sadly, 16 years later, an even greater catastrophe struck the city of Houston.
Allison should remind us that any storm can be devastating, no matter how strong it is, and it’s up to us to understand the vulnerabilities of our communities and prepare accordingly. Unfortunately, it usually takes a tragedy to bring about meaningful change. Mother Nature teaches us hard lessons. It’s up to us to listen.
Hurricane Isabel, September 2003 – Just four years after Floyd, a Category 2 hurricane again brought devastating flooding to the Mid-Atlantic region. Isabel was a classic Cape Verde hurricane. It formed from an African wave late on September 5 about 50 miles west-southwest of the Cape Verde Islands. Within 36 hours, it was a hurricane, which it would remain for nearly two weeks. For the next three days, it churned northwest through a weakness in a high pressure ridge to its northeast into the open central Atlantic. During that time, it rapidly intensified into a Category 4 hurricane.
On September 10, Isabel ran into the large Bermuda High. The Bermuda-Azores High is a largely constant ridge of high pressure high in the atmosphere that ebbs and flows between Bermuda and the Azores Islands. It is the dominant force that steers tropical cyclones through the Atlantic. When it intensifies and builds west, it acts to force hurricanes west toward the Caribbean and US mainland.
Now beneath that high, Isabel turned west and found itself in near-perfect conditions. It exploded into an incredibly powerful hurricane. Just how powerful Isabel got isn’t entirely clear. Pressure nosedived a remarkable 33mb in just 30 hrs between September 10 and 11th. On the 11th, Air Force reconnaissance aircraft recorded winds as high as an astounding 230mph inside the eyewall at an altitude of 4,500 ft. Friction reduces wind speeds closer to the Earth’s surface and an average of surface observations from the aircraft resulted in a peak intensity of 165 mph, still making Isabel a Category 5. However 230mph that close to the surface is insane and it’s likely stronger winds at least periodically reached the surface. Isabel was a monster.
By September 15, the hurricane reached the western edge of the ridge and slowly swerved back to the northwest, aimed right for the coast of North Carolina. Fortunately for North Carolinians, Isabel got a blast of wind shear that reduced it from a Category 5 down to a Category 2, but the storm would weaken no further. Normally, hurricanes like this would recurve around the ridge and out to sea. This time, the ridge stayed strong enough to keep Isabel going northwest. Unlike with Floyd, the forecasts nailed it. Three days out, the forecast landfall was within 40 miles of where it actually occurred. The resulting mass evacuations of North Carolina’s Outer Banks saved countless lives.
The history and geography of the Outer Banks has been shaped by hurricanes. Over the years, storm after storm has remade the coastline. It’s a legacy that is plain to see. The 200 mile span of the Banks is cut by dozens of ever-evolving inlets, most of them created by hurricanes. Most significant hurricane impacts on the Banks will leave a new inlet behind as a calling card. As years pass, many will fill in and disappear and then a new hurricane will come along and open a new one. Thus is life on the Outer Banks.
Drum Inlet is actually a group of three inlets midway between Cape Lookout and Cape Hatteras that have been carved out of the Banks by over a century of hurricanes. It was first created by a major hurricane in 1899 that had devastated Puerto Rico and was the longest-lived Atlantic hurricane in history. Over the years, it closed and was reopened by a hurricane in 1933 and Hurricane Dennis in 1999 (less than 3 weeks before Floyd). Isabel was about to leave its own legacy.
It plowed into Drum Inlet on Thursday, September 18 with 105 mph sustained winds. Isabel brought a storm tide of at least eight feet, leaving the barrier islands underwater in many places. Numerous homes were destroyed or severely damaged. Most homes in the area are built on pilings to allow storm water to pass under them. However, many of them were washed off their pilings and carried some distance. South of Cape Hatteras, north of where Isabel came in, a new inlet formed called Isabel Inlet. It was Isabel’s calling card. The inlet was ultimately filled in by engineers in the aftermath of the hurricane, a decision not everyone agreed with, as hurricanes and the changes they make are seen as a natural part of the evolution of the Banks.
The damage Isabel caused on the coast was severe, however the real damage happened inland. Isabel had a very large circulation and unleashed a torrent of rainfall. Extensive flooding occurred along the Pamlico and Neuse Rivers, most of it surge related. Unlike in Floyd, North Carolina managed to escape the worst of the flooding. Hardest hit was actually Virginia. A large storm surge was driven into Chesapeake Bay and many of Virginia’s rivers flooded, with a height of nine feet being recorded along the James River in Richmond, where there was widespread flooding. Downtown Norfolk was blasted by hurricane force wind gusts, storm surge, and battering waves. The historic Harrison Pier along the Norfolk waterfront was destroyed. Many parts of Hampton were underwater from storm surge and river flooding. Inland, up to 20 inches of rain fell across the state, causing widespread flash flooding. Rivers across the Shenandoah Valley burst their banks, with the South River cresting at nearly 14 ft.
The damage extended along the Potomac into the Washington DC area. Isabel was the worst tropical cyclone impact to the DC area in living memory. Over 200 homes and condominiums were destroyed across Fairfax County in northern Virginia as the Potomac overflowed its banks. Wind gusts nearing hurricane force blasted Alexandria. At the Tomb of the Unknown Soldier in nearby Arlington National Cemetery, members of the US Army 3rd Infantry have patrolled around the clock, 365 days a year since 1925…a tradition they maintained even through the worst of the hurricane. A popular urban legend emerged following Isabel that claimed they defied orders to leave their post and seek shelter. In reality, there was never a fear for the soldiers’ safety and there were contingency plans for guards to stand watch from inside the adjacent guard house if necessary…plans that were ultimately never needed. Throughout Virginia, 36 people were killed, making it the worst hurricane in the state’s history.
Flooding continued into West Virginia as Isabel continued northwest, weakening and spreading out. The South Branch Potomac River crested 24 ft above flood stage, leading to widespread flooding. However, the rains were finally beginning to wane. High winds caused widespread power outages across the northeast, but flooding was much less severe beyond the Virginias. Isabel finally evolved into a non-tropical storm system just north of Pittsburgh and faded away over eastern Ontario. But the damage was done. Isabel brought the Mid-Atlantic’s second devastating, hurricane-borne flood event in four years, and offered yet another reminder that a hurricane’s dangers extend far beyond the coast.
Hurricane Charley, August 2004 – Activity in the Atlantic Basin has always run in cycles. These cycles have ebbed and flowed ever since reliable records began before the Civil War. They are linked primarily to jetstream and ocean current patterns that evolve over long periods of time. An uptick in activity had been expected for years, with the Atlantic having entered a new active phase in 1995. However the historic onslaught of 2004 and 2005 defied belief and led to revolutionary changes in hurricane science, awareness and preparedness.
The west coast of Florida, which includes the major commercial port of Tampa, has been remarkably lucky when it comes to hurricanes. No major hurricane had struck the west side of the peninsula north of Cape Sable in 40 years, which made what happened that day in August all the more shocking. Charley formed from a tropical wave that left the coast of Africa on August 4, organizing into a tropical depression in the southeastern Caribbean.
Moving quickly northwestward around the edge of a high pressure ridge, the storm strengthened steadily. By the time it raked by Jamaica, it was a Category 1 hurricane. The island suffered extensive wind damage, but rainfall was remarkably light. Charley continued to intensify as it approached Cuba, plowing into the island as a major hurricane with 120 mph sustained winds. A 13 foot storm surge inundated the south coast, wiping out some small villages. Havana was blasted by hurricane force winds that damaged or destroyed 70,000 homes and knocked out power to much of the city for 12 days.
Concern in Florida was growing. Initial forecasts took Charley right into Tampa Bay as a major hurricane. The famously-lucky city hasn’t had a direct hit from a hurricane that strong since 1921 and is very vulnerable to storm surge. Nearly 2 million people were ordered to evacuate, including all of Pinellas County, where St. Petersburg-Clearwater is. An estimated 1.42 million ultimately fled the coast in the state’s largest evacuation since Floyd five years earlier (which famously missed the state…a fact that was undoubtedly on the minds of the hundreds of thousands who stayed). However, Charley had one more surprise up its sleeve.
By dawn on Friday, August 13, the hurricane had moved off the coast of Cuba as a Category 2 with a 110 mph winds, on its predicted north-northeast path toward the Tampa metro. However in just seven hours, Charley exploded into a monster Category 4 with 150 mph winds and turned hard right into Charlotte Harbor nearly 100 miles to the south. The effect was catastrophic. Punta Gorda and Port Charlotte, which had been expecting just a close brush, were blasted by winds well over a 100mph, obliterating hundreds of homes. Charlotte Regional Medical Center recorded a gust of 172 mph, the highest wind speed recorded in a US hurricane since Andrew hit 177 twelve years earlier. 80% of homes across all of Charlotte County were damaged or destroyed.
The hurricane passed directly over North Captiva Island and cleaved it clean in two. The storm surge peaked at 10-13 feet near Naples, however, despite impacting a heavily populated area, damage was limited to the immediate coast and lighter than expected. The real story, like with Andrew, was the wind. The small, fast-moving hurricane tore through the heart of Florida like a tornado. Mobile home parks throughout the path were annihilated. The destruction extended well inland, even as the storm quickly weakened. 95% of buildings in downtown Arcadia, 45 miles from the coast, were damaged.
Orlando was hit with winds gusting to 105 mph, causing widespread major damage throughout the city and blowing down numerous trees. The Orlando area had many large, heavy southern oak trees that had withstood upwards of a century of hurricanes. Charley blew many of them onto homes. The storm emerged into the Atlantic Ocean early on the morning of August 14, having ripped through 200 miles of the Florida Peninsula in just eight or so hours. In that time, Charley caused a staggering $14 billion in damage and left thousands of buildings in ruins. 29 people died in Florida.
The hurricane made landfall again in South Carolina as a Category 1 with winds of 80 mph. A storm surge as high as seven feet may have hit the Myrtle Beach area, however damage was largely limited to beach erosion. Charley weakened quickly over eastern North Carolina, merging with a frontal zone as it emerged back out over the Atlantic for the last time. Throughout its path, Charley killed 35 people and caused $16.9 billion in damage, at the time making it the second costliest hurricane in US history after Andrew. It would not hold that position for long. Unfortunately, this was just the beginning for Florida and the 2004 hurricane season.
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