More things we didn't know as we prepped for our first hurricane: how to intrepret the timing info in forecasts. What you need to know.

Hurricane Prep: How Much Time Do You Have

If there is a hurricane headed towards you, a big question is always “how much time do I have to get ready?”

The answer, we’ve come to realize, isn’t always so clear.

Many forecasts estimate when the storm will be “at” a particular place or when it will make landfall. It’s important to know that most of these forecasts, notably including those from the (US) National Hurricane Center, are talking about the location of the center, or eye, of the storm. Gale force winds (35 knots) will extend out considerably from the center and most of us consider their arrival to be the “start” of the storm.

Once gale-force winds reach a location, you really can’t do any further prep. It will also be extremely difficult to evacuate — even trying to get to a safe place ashore by dinghy, let alone if you’re in an area that requires evacuation further inland.

So the first important point is to know how a particular forecast that you are looking at is reporting time and location of the storm. Some, such as Chris Parker, do talk about the time that all preparations should be complete. But even with these, it’s helpful to understand the logic.

So the first question is when will the gale force winds reach you? And if you’re going to evacuate, how long before then do you need to be leaving?

It seems like a simple math problem from there: how far away is the storm (center), how far out do gale force winds extend, how fast is the storm moving toward you.

I say seems because there are two unknowns in the equation, one major and one somewhat more minor.

  • The speed of the storm can vary considerably both over time and from what is forecast (this is the major unknown)
  • The size of the storm can change, with gale force winds reaching out further — or not as far

Hurricane forecasting gets better every year, but a forecast is never a guarantee of what it will do. So I look at the National Hurricane Center forecast (and usually read info from other forecasters). From these, and with a chart (either paper or electronic) I do the following:

  • Mark the current location of the center of the storm
  • Figure out how far it is from my location (straight line — assume the worst that it heads straight at me)
  • Find out how far out the gale force winds extend
  • Find out how fast the storm is forecast to move

But then I go a step further and read the NHC Forecast Discussion to see how confident the forecasters are about the timing. I can’t overestimate the importance of reading the discussions — often you’ll discover that there is considerable uncertainty with the track, strength or speed of the storm!

From there, I do some quick calculations about how the timing changes with possible changes in speed (they usually don’t call for greatly increasing storm diameters, but if they do, I’ll do some alternate calculations to take that into effect too).

And remember that if you need to get things secured ashore and travel inland, you have to allow time for that before the gale force winds hit. So if you need 3 hours ashore to get to safety, subtract that as well to figure out how much time you have to prep and when you need to be off the boat.

Now for the story behind this post. You knew there had to be one, right?

You see, with our first (and most serious) hurricane, we didn’t really think about what it meant that “the storm is 200 miles away.” (My only excuse is that we both came from the Midwest and blizzard forecasts usually tell when the snow will start, not when the center of the storm will pass overhead . . .) We figured that if it was 200 miles away and moving at 4 knots, we had 50 hours to be ready.

No, even if it kept moving at 4 knots we’d only have about 25 since the gale force winds went out 100 miles. So we’ve just gone from two days to finish preparing to one. We should have figured that out, but interestingly, none of the hurricane prep material I read said anything about the forecast storm location being the center . . . it was just assumed that any idiot would know this. Well, we were the “better idiots” who didn’t. And it seems like no one else in our hurricane hole thought about this, either.

BUT — the storm didn’t keep moving at 4 knots. Overnight, it sped up to 20 knots. Instead of having at least all day to double-check our work, we had less than an hour from when we woke up. All the high-priority things had been done the day before, and we came through the storm with no damage.

And that has made me a huge advocate for first, understanding how to calculate how much time you might have from the forecast info; second, having a checklist with the high-priority items clearly marked; and third, actually doing the high priority items first.

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