Between 1963 and 2012, only 11% of tropical cyclone (hurricane and tropical storm) deaths were due directly to the wind. Yes, hurricane-force winds can be frighteningly destructive and frankly awe-inspiring, but when the numbers are tallied, water is undeniably the deadlier threat. Combined, storm surge, inland flooding due to heavy rains, and high surf are responsible for 88% of tropical cyclone deaths. The storm surge alone kills nearly half of all people who lose their lives during these events.
The reasons for this are simple but not necessarily obvious.
Especially in areas with modern building codes and construction, structures can withstand long duration strong winds. Even when structures are significantly damaged by debris or the wind itself, they continue to offer some shelter and protection from the wind. This is why people in the path of a tornado are advised not to jump in their car and drive away but rather to shelter in place in an interior room on the lowest floor. The roof can be ripped off a building and the exterior walls toppled, yet a tiny bathroom or closet often remains intact and offers a pocket of safety amidst the chaos.
Water is different. It rises inexorably, under doors and through windows. No room is safe. Entire neighborhoods are engulfed at once – there is no accessible safe haven once the water begins to rise. Storm surge water seethes with debris, from toxic waste to power lines to floating vehicles. And unlike the wind, which weakens quickly as a storm departs, storm surge and inland floodwaters can engulf a region for days to weeks. Those who don’t drown during the storm are often trapped without water or food until rescue personnel arrive, and when the impacted area is large and damage is extensive, rescue can be slow coming.
If you were watching news coverage as Hurricane Matthew marched menacingly up the east coast of Florida earlier this month, you probably noticed that meteorologists and local officials were focusing far more on the potential for unprecedented storm surge than on the storm’s maximum winds, despite Matthew being a Category 3 or 4 storm with winds up to 145 mph at times. Major Florida cities along the Atlantic coast and along the St. John’s River (which empties into the Atlantic Ocean just east of Jacksonville, FL) were threatened by a storm surge unseen for at least a century.
Matthew was a major hurricane with destructive winds, but it was the water, not the wind, that led governors, mayors, meteorologists, and emergency managers alike to issue impassioned pleas for those in the path of the storm to evacuate. Like hurricanes Sandy, Ike, and Katrina before it, Matthew testified to the fact wind tells only part of the story of a cyclone’s destructive power.
The rest of that story, and the far deadlier chapters, are told by water.
And starting this year, emergency managers, public officials, and the general public have another tool to evaluate the impact of that water on their communities. Developed by the National Weather Service and made operational for the 2016 hurricane season, Potential Storm Surge Flooding Maps are specific to each tropical cyclone and show a reasonable worst-case scenario for storm surge inundation at the neighborhood level. In other words, it shows the storm surge heights that a person should prepare for before a storm, given the uncertainties in the meteorological forecast.
The Potential Storm Surge Flooding Maps are based on the existing National Weather Service (NWS) Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model. (Modeling involves a dizzying and inescapable array of acronyms.) The SLOSH model takes into account forecast uncertainty and, when run as an ensemble, provides an envelope of possible storm surge outcomes based on the current forecast.
Ensemble modeling involves running a model (or group of models) many different times, each time with small differences in the initial conditions or model assumptions. For the SLOSH model, these differences represent plausible futures for the track and intensity of the hurricane given current observations and historical forecast errors. The result is a set of possible storm surge scenarios, with each member of the set representing a slightly different hurricane track and intensity.
Once this set – or “ensemble” – is assembled, it is analyzed statistically to determine a reasonable worst-case storm surge scenario at each location, and the depth of that storm surge is displayed on the Potential Storm Surge Flooding Maps. In this instance, “reasonable worst-case” is defined as that storm surge depth which has a 1-in-10 chance of being exceeded at each location. (In other words, at any given location, there is a 90% chance that the actual storm surge will be less than or equal to what is displayed on the map, given the current forecast.)
The Potential Storm Surge Flooding Maps are a valuable visual tool to assess storm surge risk as a tropical cyclone approaches land. The SLOSH model that forms the basis of the maps takes into account the factors most critical in determining storm surge:
However, the potential storm surge flooding map does not take into account a number of factors that do not impact storm surge directly but that nonetheless greatly impact overall flooding and water damage. The maps do not account for:
Wave action can significantly increase the impact of storm surge along the immediate coast, overtopping seawalls and sandbags where the storm surge alone would not. The potential storm surge flooding maps show only the potential storm surge – they do not provide any information about expected wave height. In many cases, the height of waves riding atop the storm surge can exceed the height of the storm surge itself.
Information about expected wave height and wave action impacts can be found in hurricane-related text products from the National Weather Service, including the local area forecast discussions and hazards and impacts statements. Interests along the coast and in areas protected by levees should pay particular attention to the impacts of wave action and weigh those impacts in addition to the direct impacts of the storm surge when making hurricane preparations.
Freshwater and Inland Flooding
Flash flooding, areal flooding, and river flooding due to excessive rainfall are responsible for over one quarter of all tropical cyclone-related deaths and can impact areas far inland and outside of the storm surge risk area. Hurricanes and tropical storms can dump tremendous amounts of rain in a short period of time. Even weak tropical systems can produce devastating amounts of rain. For example, the remnants of Tropical Storm Amelia in 1978 flooded central Texas with four feet of rain. Interests in low-lying areas prone to flooding and along creeks and rivers expected to be impacted by a tropical system should pay careful attention to rainfall forecasts and expected impacts.
Forecasting the protection offered by levees during a tropical cyclone is complex and difficult, as Hurricane Katrina tragically demonstrated in 2005. Wave action, the depth and speed of the storm surge, and the strength and construction of the levees all influence the amount of protection they provide. Interests living in leveed areas need to remain especially vigilant as a tropical cyclone approaches, and consider all relevant risks, not just those posed by the storm surge.
The potential storm surge flooding maps issued during Hurricane Matthew’s approach of Florida’s east coast offered a clear and dire assessment of the risk for unprecedentedly severe storm surge inundation.
The maps for Hurricane Matthew were so dire because the worst-case scenario was squarely within the cone of uncertainty. It wasn’t just possible. It was likely that locations along the east coast and the St. John’s River would be under several feet or more of water if the hurricane continued to hug the coast or made landfall in northeast Florida or southeast Georgia.
More than just the beaches were under threat. The potential storm surge flooding maps showed areas along the St. Johns River — inland regions that don’t typically think of themselves as vulnerable to storm surge –- under up to 6 feet of water as Matthew pushed a wall of water at the coast and up the mouth of the St. Johns. Although the worst-case scenario fortunately did not materialize, reports were still received of the St. Johns River flowing backwards on the morning of Saturday, October 8th, as storm surge and hurricane-force onshore winds pushed the sea inland.
“Fortunately” is the correct word in this situation, because it was nothing more or less than luck that prevented a truly worst-case scenario from actualizing. Had Matthew drifted 20 miles farther the west, the Atlantic coast of Florida, and inland river cities like Jacksonville and Palatka would have experienced truly devastating flooding.
The National Weather Service’s new potential storm surge flooding maps provide a graphical, easy-to-understand, quantitative assessment of storm surge risk along the U.S. Gulf and Atlantic coasts. By displaying a reasonable worst-case scenario at each location, they show both local officials and the general public the storm surge depth for which they should prepare themselves, enabling well-informed preparation and evacuation decisions.
However, these maps are not intended to offer a complete picture of water-related risks associated with tropical cyclones. They do not take into account wave action (i.e. waves riding atop the storm surge), rainfall-induced flooding, or potential levee failures. These impacts must be considered separately when assessing the impact of a hurricane or tropical storm in a given area.
And, as always, the output of any model is only as good as its input.
Ultimately, the accuracy of the potential storm surge flooding maps depends on the accuracy of the hurricane track and intensity forecast. Those forecasts – and the storm surge inundation maps derived from them – are continually refined as new data from in-situ and remote sensing platforms (like hurricane hunter aircraft measurements and satellite imagery, respectively) as well as new model guidance become available.
Ah, springtime – the season when life, greenery, and sandals return to the land and towering storms return to the sky.
Severe weather is already visiting parts of the southern Plains this year (including Oklahoma and Texas), and it will soon begin its annual march northward across the country as winter gives way to spring and summer.
Severe storms are fueled by the tremendous energy of an unstable atmosphere, where cold air vies with warm in a perennial battle for territory. Storms fire up and ride along the front lines – sentinels flashing, booming, blowing, and occasionally swirling their way across the landscape. For this reason, there really is no true, nationwide severe storm season – that clash of warm and cold air masses occurs at different times of year across different regions of the country, resulting in regionally variable storm climatologies.
Typically, storm season ramps up first in the South, where warm air returns earliest (or never really leaves): the Gulf Coast states experience severe storms, including hail and tornadoes, every month of the year. During late winter and early spring, severe storms in the South are usually triggered by strong cold fronts that also bring heavy snow and ice to more northern latitudes.
As March slides into April and May, the southern Plains see the annual resurgence of supercell severe storms, fed by warm Gulf moisture pulled northward on southerly spring breezes and triggered by strong midlatitude storm systems that sweep out of the Rockies. Supercells – a specific type of thunderstorm that is highly organized, long-lived, and characterized by a persistent region of rotation (the mesocyclone) – are responsible for some of the world’s most damaging severe weather, including almost all significant tornadoes (EF2 or greater) and most giant hail.
During June and July, the jet stream shifts northward, steering storm systems (and their accompanying entourage of thunderstorms) into the northern Plains and upper Midwest, where storm season peaks in mid-summer.
But don’t get too attached to the timeline – severe weather doesn’t respect the notion of a “season” and can strike well outside the boundaries of what’s considered the climatological norm, as winter tornado outbreaks so destructively illustrate.
Because of that variability in when severe weather strikes, it’s an excellent idea to remain storm ready throughout the year. However, that first window-rattling rumble of thunder in the spring can certainly provide a little extra motivation and a helpful sense of urgency. Below are some essential storm preparations to ensure that you and your family are ready to weather the storm (pun intended).
Trees are beautiful, stately, and attract a wonderful diversity of wildlife. Deciduous trees are also great for your utility bill: providing leafy shade in the summer and allowing the sun to warm your home unimpeded during winter. But if not properly cared for, they can become highly efficient house- and car-crushers during wind storms.
Before the howling winds of spring start blowing across your newly leafed-out trees, call in a reputable arborist or tree trimming company to remove unhealthy limbs and trees and to shape healthy trees to be more wind-resistant. Services typically cost a couple hundred dollars (for basic limb removal) to a couple thousand dollars (for removal of entire trees), and are ideally performed every 3-5 years. A few hundred bucks in preventative maintenance now can save you not only your insurance deductible but also the hassle of major car and home repair.
Speaking of insurance, now is the perfect time to make sure you have enough and the right type of insurance. Dust off your insurance policy documentation – or better yet, call your insurance agent for a comprehensive review of your policy. Is your deductible affordable in your current financial situation? The purpose of having insurance is to use it when you need it, so make sure your deductible is an amount you can afford to pay should your home or vehicle sustain damage.
Review your coverage amounts for the structure and its contents – if the worst happens, will your insurance policy pay enough for you to repair or replace your house and belongings? Know whether you have replacement coverage (i.e. the insurance policy will pay for a brand new item equivalent to what was lost) or whether your policy covers only the depreciated value (i.e. the value of a used item equivalent in age, wear and tear to what was lost). Is the type of coverage you have what you need? Have you recently purchased any high-value items that might need to be insured separately as valuable personal property?
Consider purchasing flood insurance if you haven’t already. Standard homeowners’ policies do not cover flooding, whether from severe storms (flash flooding), prolonged rain (areal flooding), snowmelt, hurricanes, or even sewer back-ups. With an average flood insurance claim of $42,000, that’s not a check you’re going to want to write.
You don’t have to live in a designated floodplain to experience flooding – a third of all federal disaster assistance for flooding goes to people outside of mapped high-risk areas. In fact, if you don’t live in a flood plain, you’re likely to get a preferred rate on your flood insurance policy ($35/mo is the average premium for low-to-moderate risk properties). Flood insurance is offered through the federal National Flood Insurance Program (NFIP) and can be purchased through your insurance agent.
What you don’t know can, in fact, hurt you. This is especially true when it comes to severe weather. As technology becomes ever more sophisticated, the channels through which we can receive about information about wicked weather headed our way has rapidly expanded.
Despite the myriad new options, a NOAA weather radio is still an easy, relatively inexpensive, and extremely reliable means of receiving weather alerts even when you’re not by your TV, phone, or computer. There isn’t one brand of weather radio – instead, NOAA maintains a network of radio stations broadcasting information directly from the nearest National Weather Service office, including forecasts and weather warnings. These stations broadcast on a fixed set of frequency channels, and any commercially-available emergency radio worth buying will come pre-programmed with them.
When comparing weather radios, look for those that:
For those whose cell phones have become a fifth appendage, Wireless Emergency Alerts (WEA) put critical information right in the palm of your hand. WEA messages are overseen by the FCC and include Amber alerts, presidential messages, and weather warnings. Many if not most newer cell phones are already capable of receiving them. Participation in the WEA program is voluntary but also widespread among mobile carriers. If your phone is WEA-capable, you can choose which WEA messages you receive (with the exception of presidential messages, which are mandatory), so check for instructions specific to your phone make/model to ensure that WEA weather alerts are enabled.
Another mobile device solution is the use of apps. A wide variety of apps will send you a text or alert you through the app itself if hazardous weather is headed your way. The National Weather Service maintains a list of apps, and you can check around for other options. Be aware, though, that cell phone service can be interrupted during and after a major storm – it’s wise to have a back-up means of receiving weather information in case cell service is disrupted.
Once you know a storm is coming, what are you going to do? The National Weather Service’s Weather-Ready Nation campaign and The Department of Homeland Security’s ready.gov have resources for a number of specific weather hazards, including thunderstorms, tornadoes, floods, and hurricanes. Read through the information for the weather hazards that can impact your area, and formalize a storm plan for each. Make sure everyone in your family knows what the plans are, and practice the plans, especially if you have small children. Some things to consider: where will you go during a severe thunderstorm or tornado, when a hurricane threatens, when floodwaters rise? How are you going to get information as the weather unfolds? Where do you keep your storm kit?
Speaking of storm kits – it’s a really good idea to have one and to keep it in or near your storm shelter (i.e. basement; lowest-level interior, windowless room; or safe room). If you already have a storm kit: excellent! Time to check and refresh the supplies. If you don’t already have a storm kit, it’s time to put one together. Ready.gov and Weather Underground both have thorough checklists for building a basic storm/disaster kit.
At a minimum, storm kits should include food and water, a first aid kit, medicine, sanitation products, supplies to shelter in place (tarps, duct tape, etc), gloves, basic tools for turning off utilities, flashlights, a portable radio, extra batteries, signals for help (whistle, flare, etc), and infant and pet supplies if applicable. You can expand your kit to include other useful but not necessarily critical supplies based on your own needs.
We know it’s a lot to think about, but preparing now — before severe weather strikes — will save time, money, and heartache down the line. At a minimum, you’ll have peace of mind knowing you’ve mitigated against preventable damage, planned how you’ll ride out the storm and its aftermath, and insured your property against loss. And if storm season happens not to spare you this year, you’ll have much more than just peace of mind. You’ll have the tools needed to weather the storm.
3150 days, give or take a few. That’s how long it’s been since a major hurricane, defined as a Category 3 or higher storm, has made landfall in the U.S. The previous record was about 2250 days, almost 2.5 years shorter. Although the time between major hurricane landfalls has varied significantly since 1900, it’s been about 500 days (or every 1-2 years) on average.
So, are we really due?
It’s hard not to think so. After all, if we flip a coin 8 times (for the last 8 years in which the US escaped a strike by a major hurricane) and all 8 come up heads, we start thinking, “It’s bound to come up tails next time.” But we’d be wrong (well, unless the coin was rigged). Statistics just don’t work that way. Each coin flip has the exact same 50/50 probability of heads/tails, regardless of the pattern of results that came before. So the fact that we did not suffer a major hurricane landfall last year or the year before does not in any way influence the probability of a landfall this year.
What does influence the probability of a landfall is the number of storms that form and the atmospheric steering flow that guides those storms toward or away from the US coastline. This year, an El Niño pattern is expected to form during the summer or early fall, bringing warmer waters to the eastern equatorial Pacific Ocean, and, among other things, stronger vertical wind shear, stronger trade winds, and greater atmospheric stability to the Carribean and tropical Atlantic Ocean. Strong vertical wind shear inhibits tropical cyclone development, as it tends to rip nascent storms apart before they have the opportunity to organize and develop, and enhanced atmospheric stability does just what it sounds like – stabilizes the atmosphere and hinders storm formation. For these reasons, moderate to strong El Niño years are often associated with below-average hurricane activity in the Atlantic basin.
In addition to the predicted development of El Niño later this year, Atlantic sea surface temperatures (SSTs) in the main tropical cyclone development region are expected to remain slightly below average throughout the June 1 – November 30 hurricane season. Tropical storm systems draw their energy from the warm waters over which they develop – cooler water means less energy and, generally, fewer and less intense storms.
These two major factors – the expected development of El Niño and cooler sea surface temperatures in the tropical Atlantic – have led most hurricane forecasters, including NOAA, to predict an average to below-average hurricane season for 2014.
Given the lack of a major hurricane landfall in the US during the last 8 years and the below average 2014 Atlantic hurricane season forecast, the most dangerous part of this year’s hurricane season may be complacency. We would do well to remember that it only takes one storm to create devastation (like Hurricane Andrew in 1992 that struck during an otherwise quiet season) and that even non-major hurricanes can bring widespread destruction (Hurricane Ike in 2008 and Sandy in 2012 come immediately to mind).
Both Ike and Sandy go to show that the sustained wind speed of a tropical cyclone (and therefore its Saffir-Simpson category) does not solely determine its destructive potential. The physical size of the storm is also a critical determinant of its storm surge, and water kills far more people and destroys far more property than wind.
The danger that storm surge poses to life and property is often poorly understood outside of the meteorological community (despite the well-publicized tragedy and horror brought by Hurricane Katrina’s storm surge in 2005). To address this common knowledge gap, the National Weather Service will begin issuing experimental Potential Storm Surge Flooding Maps for the U.S. East Coast and Gulf Coast during the 2014 hurricane season. For each hurricane that is forecast to make landfall, the storm surge maps will show the geographical areas where storm surge could occur as well as how high above ground level the water could reach in those areas. The maps are intended to provide a reasonable estimate of the worst case scenario for flooding in those areas that could be impacted by an approaching storm.
Last week’s National Hurricane Preparedness Week, highlighted the many dangers associated with tropical cyclones, including storm surge, inland flooding, and wind. These hazards, especially inland flooding, wind, and severe thunderstorms, can affect locations hundreds of miles from the coast, so hurricane preparedness isn’t just for those folks lucky enough to live where most of us only vacation. Chances are, even if you don’t live near the coast, you have friends or family who do. Both the National Hurricane Center and Ready.gov offer excellent resources related to understanding and preparing for tropical cyclones.
Many coastal states, including Florida, Louisiana, and Virginia, offer sales tax holidays when you purchase hurricane preparedness supplies at the start of the hurricane season. For those of you in Florida, like us here at Blue Skies, that sales tax holiday runs through this upcoming Sunday, June 8.
We’re hoping for a season as quiet as the forecast, but even so, we’re gathering our storm supplies and reviewing our plan. We hope you’re doing the same!