RV Weather

Welcome to Atlantic Hurricane Season, 2023 edition.

I hope everyone stays safe, and that we have minimal drama from the hurricane season to come. But as we all know, “hope is not a strategy,” although hope with a tangible and well thought out action plan can be powerful. In this blog, I want to give you a few key tools to use when deciding whether or not to evacuate from a tropical storm or hurricane, and alert you to a tool that is frequently misunderstood, and often misused.

I cover basic hurricane and RV safety tips elsewhere on RV Weather. Please take a look if you’re new to RVing, new to traveling or staying in locations where hurricanes are a threat, or just want to brush up and refresh your memory for this coming season.

I like the Cone! What do you have against it?

Created over 20 years ago, the cone was an attempt (and a very successful one!) to convey where the storm was going, and how much uncertainty there was in any given track forecast. The width and shape of the cone are determined, NOT by the size of the storm, or how big or intense it is expected to become, but rather by the average position errors over the past five years for 1, 2, 3, etc. days into the future. As forecasts have improved over the years, the size of these cones have slowly but inexorably decreased. The cone size is purposely designed so that, for any given forecast, there is a 2 in 3 (or 67%) chance the CENTER of the storm will be somewhere within that cone.

Well, you might be asking, what’s wrong with all that? I have a nice clean graphic, courtesy of the National Hurricane Center, that instantly gives me a pretty good idea of where the storm is going to go. If I’m staying in New Orleans, and I see the cone is heading for Pensacola, I’ll feel sorry for those folks — but I’ll be down on Bourbon Street enjoying myself and not worrying too much about that storm.

But notice I said the cone only tells you where the CENTER of the storm is going to be (and only two-thirds of the time at that). It tells you NOTHING about the intensity, scope of destructive winds, storm surge, flooding rains or tornadoes. However, it’s such a nice graphic, it’s usually the lead graphic on many TV and web sites (including for rvweather.com) — and for some people it’s the only graphic they see, or at least pay attention to.

Over time, that area inside the cone starts to look like a ‘yes/no’ type of graphic. In the cone = bad. Outside the cone = good. It’s quick, easy, simple — and very wrong. Why would we think that? Because in years past, the average size of the cone was often roughly the same as the coastal area that was damaged.

That was especially true 10, 15, 20 years ago. For example, in 2010, the diameter of the cone at 5 days was 250 nautical miles (nm). An average Atlantic hurricane may have hurricane force winds extending 25-150 nm, and winds of at least tropical storm force out as far as 300 nm. So the 5-day error and the size of a typical hurricane were, coincidentally, not all that different from each other.

Fast forward to 2023. The day-1 forecast error for the storm’s position is 25% lower than it was in 2010 (amazing!), and the day-5 error is 18% lower (really good!). But smaller errors mean smaller cones (because the cone shows where the CENTER of the storm is going to be, right?). However, the size, scale, and scope of the impacts from the hurricane itself have NOT decreased — so a greater percentage of the significant impacts will be felt outside of the cone.

Think of this another way. In some future, perfect (weather-forecasting-wise), utopian world, imagine the day 1 forecast error is only 1 nm. The day 2 error is 2 nm, etc. so the day 7 error would be 7 nm. (Forecasting fantasy, I know). But what would the cone look like? Not much more than the skinny black line of the track itself. However, the hurricanes of this utopian future are just as big, bad, mean and nasty (I mentioned big, right?) as are today’s storms — so that “cone” is useless in telling us how far the impacts will spread, who should take shelter, who should evacuate, etc.

And there’s the paradox: as our hurricane forecasts continue to improve (hooray!), the ‘cone of uncertainty’ becomes narrower and narrower, and therefore less and less relevant in showing who should take action. More and more people outside the cone need to prepare, take cover, and potentially evacuate.

OK, I get it. Don’t use only the cone graphic for my evacuation decision. What should I use?

Fortunately the Hurricane Center has some very good graphics that can help you determine your level of risk and exposure in a much more complete sense than what the cone shows by itself.

The key graphics I use for routing, diverting, and evacuation recommendations are:

• Probability of destructive winds (50 knots or 58 mph (lets call it 60 mph) sustained)
• Peak storm surge
• Maximum rainfall and excessive rainfall outlook, for freshwater flooding

While the old hurricane adage is to “run from water, hide from wind”, if we are in our RV we may need to run from the wind as well. While RV manufacturers are loath to publish what the top-end wind speeds their RV’s are designed for when being used for camping, personally, I really don’t want to chance it in anything greater than 60 or 70 mph sustained. That’s only a high-end tropical storm — not even a Category 1 hurricane. In addition to some risk of lighter or top-heavy RV’s being blown over, once you get to these wind speeds, flying debris, falling tree limbs or crashing trees can become dangerous. We have wheels – let’s use them! If there is some reason your RV is not towable or driveable, I recommend you seek shelter in a building (one that won’t flood!) to protect yourself from those winds.

Wind

This to me is a key graphic. I use the wind speed probability graphic, specifically the probability of destructive (50 knot or ~60 mph sustained) winds. For any given location, I look at the probability for the most recent warning. If it’s greater than 10%, pay attention! Look at the trend as well. If the probability is slowly (or not so slowly) increasing with each successive warning, it’s time to think about leaving where ever you are and heading to a safer place. Will there be false alarms where, in retrospect, you did not need to evacuate? Absolutely. But think about the consequences of being wrong. Traumatic, destructive, disruptive, expensive – and possibly fatal.

Storm Surge

My second key graphic. The Hurricane Center has a product that is going fully operational this year that shows peak expected storm surge for a given location and storm. You can use this information to assess whether or not storm surge is a threat to you. If you are camping on or right by the beach, even a 1-3 foot surge could threaten your RV. 6-9 foot storm surges may come well inland. On parts of the Gulf coast, 20-30 foot storm surges are possible. Water coming up through the Bayous can circle back and around, and flood miles of coastal regions, trapping people from behind. Don’t mess around with storm surge.

Rainfall and Freshwater Floods

The Weather Prediction Center, a sister branch to the National Hurricane Center, produces both flash flood guidance and rainfall outlooks for the period the storm may impact land. Be aware that unlike storm surge, flooding rains and floods may occur dozens or even hundreds of miles away from landfall, potentially long after the winds have lost their destructive punch. RVers need to be aware of these hazards even if you are no where near the coast. If you are evacuating, try not to end up in a location that will then have destructive flooding: you’ll have to move again and undergo yet more stress and anxiety.

Tornadoes

The Storm Prediction Center, another sister agency, will post the risk of tornadoes in the vicinity of the storm that’s making landfall. These tornadoes usually spin up and spin down very quickly, making the individual funnel clouds hard to predict and hard to avoid – but it’s another reason you do not want to ride out a strong tropical storm or hurricane in your RV.

National Weather Service Watches and Warnings

It should go without saying (but I’ll say it anyways!) to please pay attention to the Weather Service Warning and Watches. Hurricane-relevant watches and warnings are posted on the National Hurricane Center homepage. All RV-relevant Weather Watches and Warnings are also on the rvweather.com homepage, updated every two minutes. You will see how the Warnings and Watches often extend beyond, and sometimes well beyond, the Cone.

If you are in a watch or warning, be it for flooding, storm surge, or wind, please do what your local city or county emergency managers ask of you. My philosophy is: if you are in doubt, leave. If you are in doubt as to whether your are in doubt, leave. There is one exception. In certain locations, usually with populated barrier islands, the emergency managers have a definite order in which they want to evacuate people, starting with the most vulnerable people and locations. If your local emergency managers specifically ask you NOT to evacuate until a certain time, please respect that request.

Key Messages

What started out a few years ago as an ad hoc attempt to convey the most important few items in a deluge of storm-related information, has now become another routine product from the Hurricane Center. Not unlike my “3 Things to Know” in each daily forecast I put out, they list the top three (or four, or five) things you should know. One quibble – they start from where the storm is to where it’s going, so you might have to skim through some bullets about Caribbean Islands before you get to impacts on the Mainland. But it’s a great single graphic if you are short on time.

Where do I find this information?

Simple! Every time the National Hurricane Center issues an Advisory, they have all the graphics I mentioned above if they are appropriate. If the storm is still many days from landfall or out over the open ocean there will be no storm surge, flooding or tornado graphics – but they will always have the track and the wind speed probabilities.

For my daily RV Weather forecasts, I also include this information. Here’s an example of the forecast I wrote for Monday morning the 26th of September (2 days before Ian made landfall). In both my short term forecast and longer term forecast graphics, I show the most recent Hurricane Center graphical summary — click on that graphic to get to the Hurricane’s center website and their products. During hurricane season, there is a graphic and link to the Hurricane Center at the end of every forecast I issue, as well as links to the Hurricane Center on multiple rvweather.com pages.

Homework 🙂

Here is the link to the National Hurricane Center’s Hurricane Ian graphic archive. Click on the cone with line graphic. You can see that starting south of Cuba, the wind field for Ian is much larger than the diameter of the cone. You can also see that the Ft. Myer area was covered with Hurricane watches and warnings, even though they were sometimes on the right-hand edge, or just beyond, the cone.

Check out the 50 knot (~60 mph) wind probability graphic. If you watch Ft. Myers, you can see how by Warning #3 (nearly 5 days out), the city is within the 10% contour. With each warning the chance of destructive winds increases, slowly at first, but then more rapidly, despite the fluctuations in the forecast track.

As a reminder the right, ‘dangerous’, or ‘dirty’ side of the hurricane will almost always have more severe conditions (heavier rain, higher wind speeds, much more storm surge, more tornadoes) than the left or ‘safe’ (‘safe’ being a relative term) side. You can determine which side is the right side by imagining you are standing behind the storm, facing in the same direction as its movement. The side to your right is the ‘dirty side’ of the storm. (In the southern hemisphere, it would be the left side, but let’s not confuse things!). Only in very special circumstances would I recommend evacuation into the dirty side. Whenever possible, you want to get over onto the safe side where conditions will be noticeably less severe.

What does the National Hurricane Center say about their cone?

Glad you asked! They even made a YouTube video about it. It’s pretty good!

A personal note

One of our life experiences has been first-hand experience with a storm surge somewhere between 25 and 30 feet coming up our street. In the 1990’s and early 2000’s we lived on the Mississippi Coast and kept our home there, expecting to return for another Navy assignment. On 29 August 2005, Katrina had other ideas. While we were among the luckiest people on the Mississippi coast (no one was hurt, our personal goods were in a moving truck coming to that location but not affected, and we had both regular and flood insurance), it’s not an experience I would wish on anyone.

I don’t make RV evacuation recommendations lightly, but trust me, you do not want to be caught in a storm surge fighting for your RV and probably for your life. You have wheels. Leave early, beat the traffic (or at least the worst of the traffic) and live to fight another day.