For almost four decades, I have worked with hundreds of businesses, both before and after a hurricane has hit. Unfortunately, I have found that most businesses have a poor understanding of hurricane wind structure and movement, potential storm surge, and forecast accuracy. In addition, the action timelines of many companies are based on hurricane misconceptions.
With the devastation of the 2018 hurricane season still fresh in our minds, now is a good time to educate yourself on the correct time to react (based on sound meteorological data) if your business is faced with a hurricane threat.
Many companies use a phased plan of action. For example, a facility might decide to take a specific action 96 hours before the hurricane arrives. But at what point do they determine that the hurricane will “arrive” in 96 hours?
Three common & unwise triggers found in many hurricane response plans are:
Let’s discuss each of these three criteria further to see why basing decisions for action on any one of them is unwise.
Some companies still use range rings to trigger their hurricane response plan. Just because a hurricane is predicted to pass within “x” miles of a company’s location does not mean that the hurricane is a significant threat to that location. In addition, knowing that the storm is predicted to pass “x” miles away does not provide enough information to make an informed decision about a potential impact timeline.
For example, Hurricane Florence was originally forecast to only affect Bermuda. In two days, the storm drastically changed course and headed straight for the US East Coast.
Hurricane-force winds often cover only a very small area with respect to the hurricane’s total wind field. Consider that typical forecast error three or four days before landfall may be several times the diameter of hurricane force winds. Triggering a significant action upon a predicted impact of hurricane force winds does not take into account forecast uncertainty. It is best to use a probabilistic approach for such triggers, incorporating a probability of wind impact into a hurricane response plan.
Many hurricane response plans incorporate an evacuation decision based on a hurricane’s predicted Saffir-Simpson category. For example, a response plan may require an evacuation of the facility only for a hurricane that reaches a Saffir-Simpson category 3 or higher, leaving crews to ride out category 1 and 2 hurricanes. However, the Saffir-Simpson classification is only a wind scale — it says nothing about potential storm surge inundation. In some cases, a category 1 hurricane could produce a greater storm surge than a category 4 hurricane. It all depends on the size of the hurricane’s wind field. Maximum sustained winds (which determine the Saffir-Simpson category) may not actually have much impact on the storm surge.
So, what information should you rely on for your hurricane plan? In consultation with a trained meteorologist, you should be looking at:
Instead of relying on a proximity trigger to set your hurricane response plan in motion, you should be consulting with a meteorologist who knows your business and concerns. This meteorologist can identify when you should activate your hurricane response plan, based on a developing storm’s location, movement and level of uncertainty in the track forecast.
Instead of expecting a given forecast to be perfect, your business should assume that the hurricane might turn towards your location and use a calculated earliest likely time of arrival. Your plan could then be modified to say “96 hours before the earliest likely arrival of 39 mph winds.” This is much clearer and allows you to take action even when the hurricane is not initially forecast to impact your area. This calculation could be made by the layman, but there are so many variables involved that it would be best left to a trained meteorologist.
Once the hurricane is within about 36-48 hours of reaching the coast, typical forecast error is low enough that the forecast arrival time of a specific wind field can be used rather than the earliest likely time of arrival. By this time, it should be clear whether or not the hurricane is heading towards your location.
Taking into account a typical forecast track error and wind field size, a probability of wind impact can be calculated for your location. If you know the relationship between time before landfall and the probability of a certain wind field impacting your location, then you can incorporate a wind probability value into your action timeline.
Thus, a timeline based on sound meteorological data would state: “96 hours before the earliest likely arrival time of 39 mph winds plus the probability of strong winds impacting your location is greater than “x” percent.” This takes into account forecast error, hurricane size, and the probability of it turning toward your location.
For more information about how to develop the recovery phase of your hurricane plan, read part two of this series.
Part 2 of the Hurricane Prep for Business Series. According to the U.S. Federal Emergency Management Agency (FEMA), almost 40 percent of small businesses never recover after a disaster. Ask yourself — how will your business continue to function immediately after a storm?