Most hurricanes tell you they’re coming. Sometimes a week in advance. That extended lead time can certainly help you prepare, but it also leaves room for doubt, confusion, or even apathy over a forecast.
This guide can help you overcome the “information overload” problem often associated with model hype, spaghetti plots, and the infamous cone of uncertainty.
First, you need a good filter (a.k.a. this hurricane guide!). Then, learn how credible data applies to your situation. And most importantly, know when to act on it.
Disclaimer: This guide was constructed based on the average forward motion of a hurricane, which is 12 mph. If the storm is moving (or forecast to move) more than 20 mph, you may want to consider shifting your response up a day.
6+ Days: Too Soon for Most Decisions
The right decision at the wrong time could be costly.
Making a significant decision six or more days from when a hurricane might come ashore is usually not justified.
Paying attention to what’s brewing in the tropics isn’t necessarily a bad idea. Long-range forecast models have certainly come a long way. But there’s a reason the National Hurricane Center (NHC) doesn’t issue a forecast for a tropical cyclone more than five days out. The science beyond that time frame is just not credible.
Team Rubicon is an organization that relies heavily on donations and volunteers to help people prepare, respond, and recover from disasters. They are acutely aware of how important timely and credible weather data is to their operation.
“It would be haphazard to start moving resources or making solidified plans, you know 6 or 7 days out,” says William Porter, Deputy Director of Operations Support.
“Trying to play hopscotch with models is costly, and we want to get our people as close to the impacts as possible without putting them in danger,” Porter adds.
It’s easy to forget how large the Atlantic Ocean is and how slow (about 12 mph) a hurricane moves. The map below represents typical lead times to first impacts for storms aimed at the continental United States. This can be used as a good first step to filtering out unnecessary hype or fear.
A long track hurricane from the central Atlantic usually presents the lowest confidence forecast within five days (yellow areas on the map above). This is both a product of distance, atmospheric conditions and potential obstacles through the northern Caribbean or the Bahamas. If a storm forms in the Caribbean or western Atlantic, the typical lead time is usually four or five days, but even these can miss the U.S. entirely.
You can save yourself some emotional energy – which will certainly come in handy later – by not stressing over the forecast model snapshots beyond five days. However, if your hurricane plan necessitates the movement of large quantities of resources, some regional planning may make sense at this stage.
Five Days: Caution with the Cone
We have a cone! If you’re in the path of the cone or close to it, there is still plenty of time. Use caution at this time when pulling the trigger on something that could turn into a costly mistake, especially if it can wait another day. The margin of error of a forecast cone from the National Hurricane Center 120 hours out is 205 miles in either direction. And this still only happens 2/3 of the time. That’s a 410-mile spread in potential landfall.
“We’re going to start moving things around five days out, calling in folks to our operations center for example. But we wouldn’t start prepositioning people that early,” Porter said.
Spaghetti plots are somewhat helpful at this time frame, as they can communicate a level of confidence in the forecast. However, make sure you follow these best practices…
- Filter out the models that don’t perform well.
- Look for groupings of the lines into two or more definable paths.
- Overlay the NHC cone of uncertainty to determine forecast confidence.
Four Days: Identify Outcomes
Every waking moment becomes increasingly critical when you’re four days from landfall. This is where an expert meteorologist can help you calculate what a worst-case scenario may look like.
You want to ensure you factor in the appropriate level of strength uncertainty, not just the track. The average margin of error on storm intensity at 96 hours is around 15 mph of maximum winds. Emergency managers often encourage preparations for one category higher than explicitly forecasted.
Forecast data is becoming much more reliable at this point, usually identifying a smaller range of potential outcomes. However, there could also be two distinct scenarios to consider. For example, the storm may (or may not) cross a landmass and weaken, or the storm may (or may not) move through an area of favorable conditions for intensification.
Three Days: Prepare for Impacts
Now it’s time to pay close attention to higher-resolution forecast models. They often exhibit the skills necessary to make difficult decisions on strategically positioning resources out of harm’s way, both during and after landfall.
William says Team Rubicon usually feels “comfortable” at the day three mark, putting his plan into action. “We know at this point we can get people as close as possible without putting them in danger, allowing them to more rapidly respond,” he says.
The most important impacts to assess at this stage are the magnitude and timing of heavy rainfall and high winds.
Flash flooding and widespread infrastructure damage can disrupt a supply chain response, sometimes hundreds of miles from where the eye comes ashore. Insights on where your trouble spots may be are credible at this time for the day of landfall, with further refinement on inland areas in subsequent days to come.
Day Two: Deadline Day
Nearly all final resource and response preparation decisions should be made today. Tropical storm conditions often arrive 12 to 24 hours ahead of landfall, which could be before sunrise tomorrow. Confidence in the overall magnitude of impact is also significantly higher, increasing your ability to complete appropriate action plans.
Storm surge depth and the precise path of the strongest winds are the two hazards most prone to shifting within 48 hours of landfall. Constantly monitoring the high-resolution model simulations mentioned in day three can help you identify subtle trends in the storm track. Updates are typically available four times per day, usually around 4 am and every six hours after that.
Another tool that Team Rubicon relies heavily on is an alerting application that can be set up for multiple locations.
William says it’s such a “relief” to his team to know that no matter where his team is, they can get timely alerts for things like tornadoes and high wind gusts.
“For our people on the ground, they have to be aware of their surroundings at all times, making sure their supplies stay secure and people they need to reach are accessible.”
24 Hours: Stay Vigilant
It is now unsafe for most outdoor tasks or traveling, but there are things to watch for as every outer band comes ashore. Tornadoes can spin up quickly and put assets at a greater risk suddenly.
A standard radar map is full of color when a hurricane is approaching. This can make it difficult to understand all of the potential threats from a storm's outer bands. Using data tools that highlight wind velocities, for example, can help you identify tornadoes that may suddenly spin up.
Hurricanes often wobble, sometimes shifting the path of the strongest winds or highest storm surge by dozens of miles. We recommend having an “always-on” tracking tool that is mobile and bandwidth-friendly to constantly watch observations and updates.
Landfall: Watch for Inland Hazards
Multiple hazards may exist for several hours, or even days, after a hurricane makes landfall. Bands of heavy rain can delay the recession of floodwaters, tornadoes can still pop up, and it can become dangerously hot and humid in the storm’s wake. Your hurricane plan should account for these complications, and the task of monitoring the weather should continue.
No two hurricanes are alike. While there are similarities in how you might prepare for one, every storm’s path and motion are unique and require strategic thought and flexibility. The timing of your implementation can be just as important as the planning itself.
We hope this guide can improve the efficacy of your response by giving you confidence in when to make those difficult decisions. We've given you several brief examples of exactly how Baron technology could benefit your organization. Let us know if you want to and discuss how our superior weather data can help you make better hurricane decisions.