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Archive for February, 2015

Making weather decisions sailing Mexico’s West Coast and the Sea of Cortez

First: a disclaimer. I am not a meteorologist or weather forecaster. Neither are you.

So, with that in mind, after two and a half years of cruising Mexico’s West Coast, with a bit of research you can still manage to pick up some useful techniques for making decisions about crossings of the Sea of Cortez, weather along your route, and general weather along parts or all of Mexico’s West Coast and the Sea of Cortez.

I am going to suggest a set of links for weather, wind forecasting of strength, gusts and direction, wave height and direction, swell interval, and tide table locations so you can enter your favorite anchorage or harbor with the maximum amount of water under your keel.

I will outline a process we use for making decisions about a route or passage we are about to attempt. The tools I suggest are only a beginning, but they are very useful–especially if you have never been in Mexican waters before.

The most common way beginning cruisers get weather in Mexico is the morning SSB radio nets, like Amigo Net, Sonrisa Net, or Picante Net.

In addition, if you are setting in a major harbor with marinas, there is almost always a VHF (your Coast Guard Radio) net in the mornings that does a weather summary. They vary in quality depending on the dedication of the person doing the thankless job of collecting the weather for everyone else.

All start with the disclaimer, I gave you above. They are not meteorologists or weather forecasters, just sailors who want to help other sailors.

In addition, many who own Single Side Band radios, have added very expensive old-style Pactor modems that operate at a baud rate similar the first years of AOL (9600 to 14,400 baud) for a couple of thousand dollars and get GRIB files which are kind of line drawings of the weather. We do not use this method for several reasons mostly relating to its objectionable, antique, obsolescent technology, and exorbitant costs (for the equipment not the files).

Thus, most of what I will show you below is free and accessible thru your radios or the internet.

Internet in Mexico is an entirely separate topic but here is a short version: If you have a laptop get a TELCEL Banda Ancha modem.  Anywhere there is a cell tower in reach, you will have internet access. If you have an IPAD or tablet that takes a phone chip … chip it with a TELCEL chip, and ditto, internet access along large parts of the coast and many anchorages.


First and foremost:  It is your boat, your lives, and your RESPONSIBILITY to look at the weather and make an informed decision.


(1)  look out the porthole (reality check)

(2)  check the satellite pics of Mexico’s waters (global view)

(3)  listen to on SSB net or pull down from internet weather forecasts  (general passage info)

(4)  check NOAA experimental offshore waters forecasts for Mexican waters (new is always better)

(5)  check weather underground for your current location if in a port in Mexico  (does it agree with #1?)

(6)  check weather underground for location to which you are headed


(7)  check Passage Weather wind predictions (click thru) speed and direction

(8)  check Passage Weather wave predictions (click thru) height and direction

(9)  check Wind Finder for wave height and period for both ends of your passage


(10)  Check tides at both ends of your passage.  (high tides estimated time of departure and arrival)

(11)  FINAL STEP  … check the Earth Wind map.  Winds and Waves models. (data three hours old)

Big sigh!


Start with the basics, look out the freaking window (portal) of your boat. Is it sunny, cloudy, windy, or calm?

This lets you double check your attempts to forecast local weather. If you do what I suggest and your carefully researched prediction doesn’t match the weather outside your porthole, welcome to weather forecasting in Mexico.  It is possible that you are either doing what I suggest wrongly, or you’re using the wrong online weather stations, or you have done everything right, and, the weather is being perverse in the extreme.

So how do you start?

Start with an online weather source for Mexico. I will supply you with three for cruisers. Use all three to get a detailed sense of the general weather for large parts of the West Coast of Mexico.

I like to look at the satellite view of Mexico’s waters first. It will tell you a thousand things very quickly.
Go here:

Look at all the pretty pictures. I like the third down which is a time lapse satellite view of Mexico’s West Coast … it will give you a lot of info quick about the general state of the area weather. You can zoom in if you are on a IPad.


It also has GRIB style line drawings for you old school types at the bottom. It loads in an instant so great to grab some weather from.


Then we go to the online Sonrisa Net weather forecast. This is an online version of the presentation they do over the Single Side Band radio network. It is very trusted. And, I usually start with the Passage Forecasts because they give thumbnails of the most common passages you will use.  The online site is here:

And, finally, we check the ‘NEW’ NOAA offshore waters for Mexico’s West Coast. This is an experimental forecast and very, very , very detailed and useful. It is currently machine generated, so no real forecaster looks at it. Use with caution, but use!

It is easiest to find here:

It is a text file. Be sure to check the time and date of the bulletin because sometimes the Vallarta Yacht Club forgets to update. Once you have it, you will have to decipher the names of the zones since NOAA decided to call the Sea of Cortez the less politically correct, in Mexico, ‘the gulf of California’. Once you get used to that, the rest is pretty intuitive.

They have only been doing this for about the last 10 months and it is wonderful. Looks to become permanent, unless, the Republican Congress can figure out a way to shut down the government again.

Once you have looked at these three sources, you have as much info as most of the people who are broadcasting forecasts on the radio.

A final check might be here, once you think you know what the weather is likely to be. Look at

Now, how to know more. You need to know more.  Repeat after me, “I need to know more!”

To really plan for a passage (coastal or crossing), you need more info.

You need local weather for where you leaving from and for where you are going too. We use Weather Underground for the ports we are headed to and from. It gives a very nice 7-10 day forecast with lots of details. And, you can adjust what station you are looking for precisely.

An example of when that is useful might be Mazatlan which used the International Airport as the default station. But, you can shift that to a station just north of the Cid marina which is then spot in for weather at the entrance to the marinas and at the breakwater.

Go here and pick a city:

This is for the City of Mazatlan. To see another, change cities. To change stations, click on nearby stations and a map will pop up … zoom in and click if you see a better location near your destination. Simple.

On our recent crossing attempt we checked Mazatlan (going from) and La Paz (going to) for the 7-10 day forecast. We needed a three day window of good weather on both sides.

It is not just about the weather generally. Because you are in a boat powered in part by the ‘weather’, you need more details.  You need wind speed and direction.

So now look here for wind speed and direction:

Click on the zones, It will take two clicks, one for eastern Pacific and one for West Coast of Mexico and Baja.
What you see will look like this.

Surface Winds SurfaceWaves

Look carefully below the images and you will see player controls like for music, advance forward, reverse, play. These controls let you advance by hourly of half day intervals to see upcoming weather and wave set directions. Play with it for the days you are thinking of doing your passage … cool, huh!

You still need more info on the waters you will cross. You know direction and some idea of height. You need more. What you need is interval or period. The time between waves. For example three foot waves from the front of your boat at 20 second intervals is not all that bad. But three foot waves at a five second interval from the front will pound you to death, shake everything in the boat loose from its cabinet, and more importantly slow you to a crawl. It will also shake up you fuel tanks causing everything from air bubbles in the fuul lines, to stuff from the bottom of the tank being mixed up with the diesel again and pumped to the engine.

Surfers love waves, unlike sailors, so, you can predict interval by using surfing sites like this:

The six lines you want to look at are wind direction, wind speed (kts), wind gusts (kts), wave direction, wave height (m), wave period (sometimes called interval).


You will already have some notion of the winds from your first three sites or the radio nets. The wave information will let you know what to expect on the hull of the boat. Short intervals or periods are choppy and hard to make headway in. They are what is classically called bashing if you are headed into them. Abeam, they make the boat rock madly back and forth like a drunken sailor. From behind you hobby horse. But, long interval wave sets are gentler (depends on height) and the boat makes good progress. Easier to handle abeam (from the side) and what is classically called following seas, if from behind.  For us, short interval/period is anything under 10 seconds and long interval/period is anything over 15 seconds.  You will adopt a range that suits your sailing style and experience after you have some of either.

Look at the port you are leaving from and the port you are going to for the nest few days of your anticipated crossing.


This is not obvious.

You will know how long you think it will take you to make your passage. You need to know the local tides for where you are leaving from and where you are going to. This may seem like too much detail, but it is not. You do not need to arrive in your big 30 hp sailboat that does 7 knots only to find that the tide is out and the depth of the entrance to the bay or harbor is 6 inches less than your boat draws. You do not need to arrive and find 6 knots of outgoing tide and a head wind. So, look at your predicted arrival and see when the days high and low tides are …


Go here and choose a port or nearby port for your destination:


I have saved the best for last. This bit of trivia will make up for not having studied weather wind and sea patterns for years. Meaning, you are new at sailing and want to learn fast.

Go here:,22.90,408

This is the earth wind map.


It is beautiful, hypnotic, calming, frightening at times and more to the point, it shows the actual winds on the planet about three hours old real time. Repeat that and listen … actual winds… three hours old … real time.

If you are careless or not paying attention, it also has a setting that will show you the planetary wave action, three hours old, real time.

Find these settings and play with it …. there used to be (and still are) entire books that contained the anecdotal and statistical info contained on this map. Based on Google Earth, you can zoom in on sections of it to get more detail.

Final caveats.

Again, I am not a meteorologist. I am a sailor. If you sail then you already know that weather, wind and waves, in particular are extremely fickle.  Once you are at sea, and under way, never ever let your forecasts interfere with good judgement based on what you are actually experiencing.  The place you are making passage to will always be there next week, next month, or next year.  Know when to say … this is not what I expected!  Know when to turn around.

Most of these require some ability to get the internet. You can use a phone, IPhone, modem, sat phone, Banda Ancha USB stick modem, wi-fi cafe, wi-fi extender antenna but you have to get on the net.  If you want weather gribs, you need a modem.

The ones that do not require and internet connection, require some form of radio be it VHF or Single Side Band.

The process described here works well for Baja and the West Coast of Mexico as far south as Manzanillo, perhaps even Zihuatenejo or Acapulco.  It is not the method for looking at weather in the far south of Mexico (namely the Tehuantepec crossing).  Other methods are needed there.


I thought I would share this because I have not seen good info for new cruisers on how to predict (0r at least get) weather along Mexico’s West Coast. I hope you enjoy and use. You do not have to learn it all at once. If you have suggestions, contact me at or leave a message here on the blog.