Tackling the Tehuantepec

7/1/2012

By Tom Morkin

During our little meander around the planet there have been about eight areas where we expected to encounter more wind than we wanted. In some of those areas, a heck of a lot more. They stand out in my memory:

  • Cape Mendocino, California
  • Alenuihaha Channel between the Island of Hawaii and Oahu
  • Cape Wessel, northern Australia
  • Strait of Mannar between Sri Lanka and the Indian subcontinent
  • Gulf of Suez in the northern Red Sea
  • North coast of Colombia, at the mouth of the Rio Magdalena
  • Northern Costa Rica and Nicaraguan area of Papagayo winds

And last but certainly not least is the Gulf of Tehuantepec in the deep south of Mexico. This nasty piece of geography and climatology we recently put behind us. Let me first give you my humble summary of the whys and wherefores of the area.

Why is the Gulf of Tehuantepec the bane of sailors’ existence when sailing between Mexico and Panama? Statistics for starters:

  • During the winter months, the percentage rises dramatically. In January it peaks when you can expect gales almost every day and storms regularly.
  • Winds of 50 to 60 knots in December, January and February are not uncommon.

Every year, hapless vessels both large and small get caught out in the 200 mile wide gulf when it shows its malicious side. Even large ships are unable to resist the storm force winds and fast building and breaking seas. Vessels have no option but to turn downwind and brace themselves for a long and frightening ride south and out to sea for 200 to 300 miles, at which point the effects of the Tehuantepec winds begin to fade.

The mechanics of these winds are not difficult to understand.

A close look at the isthmus of Mexico around Tehuantepec reveals two significant points:

  • 1) The isthmus is only 125 miles wide. That is the distance between the Bay of Campeche on the Caribbean side and the Gulf of Tehuantepec. It is so narrow that serious consideration was given to cutting a transcontinental canal here instead of Panama.
  • 2) A look at a relief or topographic map will show that this is the lowest area in the otherwise mountain studded isthmus.

These two factors taken together make a damn fine wind tunnel for those persistent winds from the Caribbean. This wind funnel is at its most dangerous when the winds from the Gulf of Mexico come from the north as so often happens when a high pressure ridge sets up over Texas. These north winds are funnelled south into the Gulf of Tehuantepec, where the wind speed is often doubled as the winds fan out into the Pacific.

Although the Gulf is about 200 miles wide, the maximum winds are squeezed through a corridor 30 miles wide. The winds in the corridor blow from the north, but as they fan out in the Gulf, the winds west of the corridor can blow northeast to east, while east of the corridor they have a northwest to west component. This behavior is of key importance to crews crossing the gulf, as we were to discover.

The conventional wisdom is that weather forecasts for Tehuantepec report average wind speeds over the entire Gulf and do not factor in the non linear nature of gap winds. The funnel effect produces shot gun blasts of wind, especially in the 30 mile gap. So, if a gale of 35 knots was predicted in the Tehuantepec, you can count on 45 plus knots in the 30 mile funnel zone. Veterans of the Tehuantepec tell you that weather forecasts don’t sometimes underestimate winds in the Gulf, they always underestimate them. Winds of 50 to 60 knots in December, January and February are not uncommon.

The most dangerous aspect of the ferocious winds is the even more ferocious sea that can rapidly build to 15 feet with only a four to five second interval. Bear in mind 15 foot seas with an 11 to 14 second interval in the open and deep ocean is a comfortable shallow sloped swell, whereas as the short, almost vertical 15 foot walls of white water in a “T- pecker” are enough to make prairie farmers out of the keenest of sea going sailors.

So what’s a pair of chicken cruisers the likes of Liz and me going to do to get across the ‘Gulf of Grief’? Fortunately, and not surprisingly, there’s a lot of good information in two of the popular cruising guides of Central America. The Sarana Guide produced by Eric Baicy and Sherrell Watson is unquestionably the most current and reliable. The recommendations offered are very explicit. One watches the weather pattern in the Gulf of Mexico and waits until the low pressure system is established over Texas. This shuts down the usually consistent northeast trade winds resulting in southerly winds in the Gulfs of Mexico and Tehuantepec. That’s the weather window one wants and hopes will stay open for the two day trip.

The problem, of course, is that these windows have a nasty habit of slamming shut quickly and unexpectedly. It is generally accepted that the only prudent strategy for the crossing then is the ‘one foot on the beach’ approach. So rather than the 235 mile straight line course from Puerto Chiapas Mexico to Huatulco Mexico, the favored route is along the shore of the Gulf about a mile offshore in 100 feet of water until the winds really howl, then moving within ¼ mile offshore in 30 feet. This adds 30 miles to the trip and doesn’t protect you from the wind but since the wind is blowing offshore, there is virtually no fetch and therefore, no big waves. In fact, anchoring off the beach if the crew is too tired to carry on is a viable option, because for the most part the shore slopes very gradually and has a sand bottom, ideal for anchoring.

The cardinal rule is to never get so far offshore that if the winds kick up you can’t sail or power upwind to get in close to shore to get in the flat water.

We spent nine days in Puerto Chiapas prior to heading across the Tehuantepec. The almost finished marina allowed boats to stay free of charge which was too good to pass up. We took advantage of the opportunity to head into the mountain town of San Cristobal. For much of that nine day period the Tehuantepec was experiencing gales so we were only too happy to head into the hills and not think about it.

Upon our return we got daily weather reports and forecasts. Rather than wait for the perfect weather window which could have meant another week of waiting, we took off knowing there would be a 12 to 24 hour period when forecasts called for 25 knots, even though we knew forecasters always underestimate the wind speeds.

After a thorough official harbor check-out, complete with a sniffing dog wearing boots, we were off.

The first 20 hours of the Gulf were as mellow as mellow could be as we motor sailed with a double reefed main and staysail. However, as we approached the head of the Gulf we saw that the mountains on shore were getting smaller and smaller until they ceased to exist as we pressed west. About that same time, the wind started to pick up around 0400 on the second morning just as I went off watch for three hours. When I opened my eyes at 0700 I immediately sensed the situation had changed. The boat was pitching to short choppy seas and I knew the boat speed would be low.

When I poked my head out of the companionway, I knew we were in for a miserable day. The wind was up to 25 to 30 knots which wouldn’t have been bad, but it was from the west northwest, right on the nose. “We’ve got a contrary current of ¾ to 1 knot. Our speed over the bottom is only 2.5 to 3.5 knots and sometimes the bigger waves almost stop us completely” reported Liz. Argh.

Since the wind was almost paralleling the shore, hugging the shore was of only marginal help.

Our buddies Greg and Deb (seen here leaving Puerto Chiapas) of the Telluride Colorado based Lion’s Paw were 20 miles ahead of us when we contacted them on the SSB ‘Amigo’ net. “We’ve just passed the ‘dragon’s maw’” (the area around Bahia Ventosa, “air hole” in Spanish, where the land is low lying and flat virtually the entire 125 miles to the Caribbean), “and we clocked winds of 37 knots” was their warning.

But the good news was that in the 20 miles that separated us, the wind direction clocked around to the north northwest, a direction we could sail. It also meant we would eventually derive benefit by being close to shore.

We just had to stick it out for another six or seven hours and keep as close to shore as we dared. It was precisely at this point that our depth sounder began to malfunction, reporting depths from 300 feet to 4 feet and then for minutes at a time indicate we were off soundings. Occasionally, it would show depths of 80 to 90 feet, which we felt was accurate, but only for a couple of seconds in a five minute period. We couldn’t trust it enough to venture really close to shore especially as we watched the surf pound the windswept shore just half a mile to starboard.

Hour after hour we watched that godforsaken, barren shoreline pass way too slowly. Salt water washed over the decks every five seconds as we — often unsuccessfully — tried to take cover behind our dodger.

By 1130 our boat speed began to slowly increase. The wind direction was changing and we actually started to derive benefit from the now strengthening wind. We were approaching the ‘dragon’s maw’ but could now lay the course. Hallelujah! The wind shift meant our speed went from three knots to sevens and eights and the seas got flat by the minute. Soon the wind was almost on the starboard beam, the engine was switched off and all of a sudden the ordeal became an incredibly exciting adventure, a joy ride. With only a fraction of our sail area in use, we smoked along at eight and a half knots thinking “that big ole dragon ‘aint so scary after all”.

By 1500 we were lamenting our lack of wind because at that time we came under the wind shadow of the mountains on the western side of the Tehuantepec. Our remaining 35 miles to Huatulco were virtually windless and by 0200 on the third morning we had the hook down. Tehuantepec was just a memory.