Interpreting Pre-hurricane Wind and Storm Surge Assessments

When the National Weather Service (NWS), in conjunction with the national Hurricane Centre (NHC) in Miami, issues a watch or warning for a hurricane, it’s hard to know whether that means you should flee or stay put and batten down the hatches.  While it is always better to be safe than sorry, making that determination for yourself, based upon the wealth of information at your fingertips, can save lives, time and money.

As soon as a tropical depression reaches sufficient strength and organization to become a tropical storm (39-74mph sustained winds), it is named, and a watch is issued for a wide swath of area that it might affect.  This includes marine watches that alert ships in the area to get out of the way or put down anchor in the nearest friendly harbour and ride it out.

Just because a tropical storm is named doesn’t mean it will develop further into a hurricane.  A very rough third of such storms dissipate from there, bringing somewhat high winds and a great deal of rain.  However, the major loss of life and property associated with large hurricanes is typically avoided.  Even regions well outside the tropics can be harassed by tropical storms as those in places as far-flung as New York and even Northern Europe can attest to.

The parent body of the NWS, the National Oceanic and Atmospheric Administration (NOAA) issues maps, freely available to all online or on television broadcasts that plot the expected landfall zone of a hurricane.  While these have been sometimes and famously wrong, they usually give a fairly good idea of where the highest winds (those associated with the “eye wall”) are likely to be found.  These become more accurate as the storm nears landfall.

If a storm seems to be building quickly and heading into hot and otherwise placid waters, NOAA will often issue an evacuation recommendation along with the hurricane watch.  Within 24-hours of projected landfall, the watch turns into a warning and it is recommended that anyone leaving had better go now or prepare to stay.  Within 12 hours, another alert will be issued, advising people to take immediate shelter no matter where they may be.

As Hurricane Rita taught many in Texas, the sooner you leave, the better.  Also, heading in a popular direction by interstate highway might be the worst way to leave town, since traffic jams that result when large urban areas are given the evacuation order.  While the NOAA and state officials recommend following interstate evacuation routes, and you will certainly want to have an evacuation route planned before you leave, it’s up to you which way you’ll go.

Sometimes, when storms seem especially bad, that evacuation recommendation may turn into an order that local law enforcement is compelled to carry out.  It is not uncommon, especially in small communities that face such disastrous hurricanes, to have the police tell people they’re on their own for the next few days if they refuse to leave.  If you’re not prepared to survive for the next week without additional food, water, medicine and other necessities, then you ought to heed the first warning and get out while the getting is good.

As for the data that these recommendations are based upon, the NOAA and NHC make constant updates to the track of each storm as satellite and airplane reconnaissance comes in.  This is matched with existing flood and storm surge maps that have been prepared over the years.  Local officials, however, usually issue evacuation notices based upon one storm category higher than that actually issued. 

For instance, someone living in a coastal area that is to be evacuated in the event of a category-3 hurricane may find himself or herself under evacuation order when a mere category-1 storm approaches, depending upon the track of the storm and the headache this is likely to cause.  Ultimately, it is a local and personal decision, though there are countless stories of people who “didn’t think it’d be that bad,” who later needed expensive and dangerous rescue from those same local officials.

Preparing for Storm Surge and Water Damage

One of the most destructive products of a hurricane is the storm surge.  A very large storm can send a 20-foot wall of water a quarter mile inland, flood second story apartments and drop boats miles from shore.  Homes are also in danger of being flooded from above when roofs are ripped off in high winds and then drenched with the many inches of rain that are commonly associated with hurricanes, even many miles from the path of its eye.  There are improvements and modifications you can make to your home, structures and landscape that will reduce you risk of being flooded, and your insurance company should reward you with lower hurricane premiums for your efforts (but don’t necessarily count on that).

As a hurricane approaches, forecasters will give it a category rating from the Saffir-Simpson scale.  This gives you an idea of how high the storm surge will be around the eye-wall of the hurricane.  For instance, a category-3 storm will have a storm surge of 9-12 feet.  Add to this any waves that are already present and those churned up by winds, and you’ve got yourself a big wave if you live on the coast.  When you see sturdy-looking homes that have been utterly destroyed, it is often this wall of water that is most destructive.

Of course, evacuating yourself from the coast when such a storm is coming is the most important thing to do, but those who take measures to protect themselves will increase their chances of having a home to come back to.  Just in case, it is always a good idea to take important papers and documents with you, if you have room.  Better yet, keep such documents inside a safe-deposit box – far inland. (The storm surge from Hurricane Katrina erased entire bank buildings from the face of the earth.)  An attic or water-tight container may do in a pinch, but be advised that the attics of single-story homes can very easily become inundated with surge water in large storms. Interestingly, one watertight container that many people have used to store valuable papers and things is their dishwasher.

Some of the repairs you might want to consider include re-enforcing your home’s connection to its foundation, whether you have a basement or are located on a slab.  Mobile and manufactured homes are especially prone to this sort of damage.  Roof gables should be checked to make sure they’d keep your roof on tight in hurricane-force winds.  Your shingles are likely to want replacing with stronger models along with an additional rooftop moisture barrier. 

Those with boats should be advised that watercraft stored in a marina are in serious danger of ending up a long way inland as a result of a storm surge wave, even if well anchored.  The combination of low pressure and winds in the area of the eye are enough to suck your vessel right off its pilings.  Check with your insurer to make sure hurricane damage is covered by your boat insurance policy.

Even homes as far as 50 miles from the coast can suffer some effect of a large storm surge.  When one is approaching, be sure you prepare your home by plugging the seams of doors and doors with tape and bracing them with something.  Put all your small objects and away and pull anything you can off the floor.  Plan on your electric being out and be very careful if the power is still on and water is flooding a room up to outlet height.  Lock your pets up in carriers that you can easily take to safety if need be. 

If water does enter your home, be careful to minimize your time spent in contact with it, since it may contain irritating chemicals, fecal matter or harmful bacteria or algae that can cause skin ulcerations and may even release aerosol toxins that can sting the lungs and eyes.

Preparing for a hurricane involves making sure you protect against it, ensure the safety of your household, and make sure you can safely and completely recover from a flood incident or storm surge caused by an Atlantic or Gulf hurricane.