How To Avoid Hurricanes

In this post we’ll cover tropical cyclones in the Weathermuffin app for sailors.

What is Weathermuffin?

It’s a unique and novel weather app for sailors—and especially world cruisers—designed by a fellow sailor.

Weathermuffin actively monitors the conditions you care about most and alerts you of uncomfortable or potentially hazardous conditions you may encounter such as…

  • steep waves
  • confused seas
  • wind opposing current
  • lightning
  • calms
  • …and more

Why use Weathermuffin for hurricanes and tropical cyclones?

If you’ve ever looked for tropical cyclone information online you’ve realized that there are myriad regional sources, each with its own particular quirks and idiosyncrasies.

Weathermuffin gives you a single, unified picture of world-wide
tropical cyclone activity… a one-stop shop for cyclone information.

Furthermore, Weathermuffin’s graphical presentation of tropical cyclones is straightforward and easy to understand—particularly, seeing the movement and intensity of storms through time in context with your vessel’s projected future position.

As you can imagine, the timeliness of tropical cyclone information is crucial. If you’ve ever read anything about the El Faro disaster of 2015, you understand this very well.

Generally speaking, tropical cyclone information is available in the Weathermuffin app within 10 minutes of its being published by the relevant government authority.

Furthermore, aside from tropical cyclone text advisories—which can be challenging for a fatigued or short-handed crew to interpret while underway—the existing data options are generally not low-bandwidth satellite data friendly.

Weathermuffin’s tropical cyclone data is optimized for quick downloading such as when using the Iridium GO!

Finally, Weathermuffin has the tropical cyclone information that is most useful to you as a sailor. That includes:

  • the track (where the cyclone has been)
  • the forecast (where it’s anticipated to go)
  • maximum wind speed, gusts, and seas
  • 34-knot wind radius, and 12-foot (3.5 m) seas radius
  • closest point of approach (CPA) and time to CPA

What geographic areas are covered?

Generally speaking, most of the world’s waters where tropical cyclone development and activity is possible. This includes the Atlantic, Pacific, and Indian Oceans, but excludes the Arctic Ocean and the Mediterranean Sea.

What information is available?

Let’s take a look at the app:

Here we’re looking at some tropical cyclone activity in the Atlantic and Pacific Oceans. Already we can see there’s a couple storms. There’s a big one over in the Atlantic Ocean, a smaller one in the Pacific Ocean, and one that is developing just to the south of that.

We can see there’s a storm track and forecast track. The red colored line is the track—where the storm has been over the last 72 hours—and the orange line is the forecast—where it’s anticipated to be in the future.

There won’t always be a forecast track… many storms are not forecast until they develop into a cyclone.

Note that the track and forecast depict the location of the storm’s center.

If we zoom in we see some additional information:

(For now we’ll focus on the hurricane “Jova” shown.)

Here we see the storm name and classification. It is a category one hurricane named “Jova.”

We may also see here storm speed and direction of travel. This is not always available with every forecast, but often is.

Just below the storm name we have the description of whether that point in time is a track or forecast point, and the time for which the location on the next line is relevant.

So in this example at 1200 Zulu on October 4, hurricane “Jova” is located at 13°18’N by 109°00’W.

Just below that we have maximum winds, gusts, and maximum seas. Here we see that the maximum wind is 75 knots sustained, gusting to 90 knots.

Just below that we have 34-knot wind radius and 12-foot (3.5 m) seas radius:

This tells us the radius at which we can expect to find 34 knot and higher winds, and 12 foot (3.5 m) seas

In this example we would start to encounter winds of 34 knots at a radius of 70 nautical miles from the storm center, and we would start to encounter 12-foot or 3.5 m seas at a radius of 90 nautical miles from the storm center.

Just below that we have closest point of approach (CPA) and the time to CPA. In this example (and based on our current position, course, and speed) we can expect to get to within 629 nautical miles of the “edge” of the storm in about 74 hours.

In this context when we’re talking about the “edge” of the storm, we’re referring to what is the larger of the 34-knot wind radius or 12-foot / 3.5 m seas radius.

So we would expect that based on this CPA information we would get to within 629 nautical miles of the 34 knot winds, or the 12 foot seas, whichever farther out from the center.

However, note the line below indicates a CPA warning:

It says, “CPA based on last data point; may be closer.”

This means that the CPA that was computed is based on the last data point that we have for the tropical cyclone. Beyond that, there isn’t further data available. It may be beyond the window of forecasting, for example.

So the actual CPA could end up being closer than the 629 nautical miles shown (we may get a newer forecast later with more data further into the future, for example).

So this warning is telling us that we need to be extra careful and monitor this storm closely, because the CPA could actually end up being closer than what is shown.

One additional thing to note: if the time to CPA is “now,” that effectively means that the closest point of approach is right now.

In other words, your vessel and the storm are likely moving away from each other, and are not expected to get any closer.

The next line tells us who is the reporting authority for this track and forecast, and how recent it is.

In this example we see that the National Hurricane Center (NHC) issued this track and forecast 42 minutes ago.

This is the time at which the information was published by the government authority that issued it.

Finally, on the last line we read that the storm graphic is an artificial depiction. This means that the storm does not actually look how it’s shown here.

However, the storm size shown is based based on the 34-knot wind radius and the 12-foot (3.5 m) seas radius, whichever is larger.

In this example we know that the 34 knot wind radius is 70 nautical miles, and the 12 foot (3.5 m) seas radius is 90 nautical miles. The larger of the two is 90 nautical miles. (The larger is chosen in order to be conservative.)

So the storm shown on screen here is depicted using a radius of 90 nautical miles:

Thus, the storm graphic shown depicts an area we’d want to avoid:

This is where the 34 knot winds and/or 12 foot (3.5 m) seas are going to begin.

Important Cautions

⛔ This should in no way be construed as suggesting that you can safely approach the depicted “edge” of the storm! Prudent seamanship dictates, for safety of crew and vessel, keeping as far away from cyclones as possible.

⚠ The effects of a cyclone (such as rain, clouds, gusty winds, and swell) may extend well beyond the 34-knot wind radius and the 12-foot (3.5 m) seas radius.

⚠ Although cyclone forecast accuracy has improved significantly over the last few decades, no forecast can be relied upon as being 100% accurate. Your ship is in your hands, and only you can make the best, most appropriate call for your vessel and crew.

We’ll now turn our attention to this disturbance that’s just to the south:

This is a disturbance… it actually hasn’t formed into a cyclone yet, so it has not yet been named. Although, it is being actively monitored by professional meteorologist as a system of interest.

This also means that it does not yet have a forecast (as evidenced by the lack of an orange track).

But we see something new here which is just below “Max wind 20 kts sustained”:

It says, “Formation chance 60% in 48 hrs, 90% in 7 days.”

This is the forecast probability of development for this disturbance. In other words, there’s a 60% chance of it developing into a cyclone in the next 48 hours, and a 90% chance of it developing into a cyclone in the next 7 days.

So this is something we would want to keep a very close eye on.

Again we have our CPA and time to CPA, as well as the issuing authority (NHC), and how recently the track was published.

Now, one interesting thing we can do in Weathermuffin is to look forward in time to see where these things are going.

If we use the time slider down here at the bottom we we can choose different points of time in the future to see how the storms move and develop in intensity:

If we slide forward in time, we see that suddenly “Jova” has very
rapidly intensified into a major hurricane with maximum winds of 115 knots:

All the information that’s displayed updates based on the selected time.

We can also see in context with our vessel’s current position, course, and speed. Looking in the top-left corner, we have our vessel with its projected future position:

In this hypothetical scenario, we’re departing out of San Francisco and heading out to sea. We can see that we might be converging with this storm “Jova,” and almost certainly want to alter course, or turn around and head back to port.

Zooming in, information is available for every point in time so we can see how all the data changes over time based on the storm’s forecast.

Returning our attention once again to the disturbance, you’ll see right in the middle it has a flashing question mark symbol:

Any time you see the flashing question mark, that means that the storm location and associated data that’s shown is more than 12 hours beyond the available data.

In other words, we’re looking at a time beyond which there is available data. And in that case, it’s not knows where the storm will be.

It could be 12 hours beyond the end of the track, or 12 hours beyond the last forecast point. But there isn’t information about where the storm will be at that time, so it’s not possible to position it on the screen at an accurate location.

So the question mark warns us, “Hey! We don’t actually know where the storm will be at this time.” It could be anywhere in that vicinity, or anywhere else for that matter.

There are a couple settings related to tropical cyclones.

Tapping the chart layers icon, we can use the Cyclones toggle to turn the display of tropical cyclones on and off:

If you’re going to download via the Iridium GO!, then you can choose whether or not to download cyclones using this option:

However, the tropical cyclone data in Weathemuffin is optimized for fast downloading over slow connections, so downloading cyclones every time is recommended.

To review, the information that is available is:

  • the storm track (in red) and the forecast track (in orange)
  • storm classification and name
  • speed and direction of travel (some forecasts)
  • maximum wind, gusts, and seas
  • 34-knot wind radius and 12-foot (3.5 m) seas radius
  • closest point of approach (CPA) and time to CPA
  • time at which the track and forecast were issued by the authority
  • 48 hour and 7-day development probability (for disturbances under investigation)

Where does the information come from?

The tropical cyclone information comes directly from the relevant government authorities. This means the National Hurricane Center (NHC) for the North Atlantic and Eastern North Pacific, and the Joint Typhoon Warning Center (JTWC) for everywhere else.

Let me stress again that the timeliness of information is extremely important. If you’re sailing in an area with active tropical cyclone activity, you’ll want to check and update the information as often as possible throughout the day.

The government authorities generally update the track and forecast a bit after the synoptic cadence of 00, 06, 12 and 18 Zulu. This means after midnight, 6:00 a.m, 12:00 noon, and 6:00 p.m. in the UTC time zone.

Again, the information is generally available in the Weathermuffin app within about 10 minutes of its being published by the relevant government authority.

What about passage planning?

If you’re looking for historical cyclone information for passage planning purposes, then you’ll want to check out the Ocean Atlas app.

It contains data for historical cyclones from 1980 onwards, as well as other up-to-date climate data useful for passage planning.

Ocean Atlas gives you the latest up-to-the-year climate data, which may not be the case for pilot charts or other printed materials.

With the effects of climate change being what they are, it’s ever more important to have access to the most up-to-date information possible.

If you’re interested in learning more about the Ocean Atlas app, click here.


In this post we covered

  • What is Weathermuffin?
  • Why use Weathermuffin for hurricanes?
  • What geographic areas are covered?
  • What information is available?
  • Where does the information come from?
  • What about passage planning?

For timely, real-time tropical cyclone information, download the Weathermuffin app today.


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