I first heard about the Gulf of Tehuantepec gales from my father who sailed with the United Fruit Company’s Great White Fleet during the late 1940’s and 1950’s. The Gulf of Tehuantepec (Spanish: Golfo de Tehuantepec) is a large body of water on the Pacific coast of the Isthmus of Tehuantepec in southeastern Mexico. The gulf extends approximately 300 miles from Puerto Angel, in southern Oaxaca state, southeastward to Barra del Suchiate, in southeastern Chiapas state, and measures approximately 100 miles across its mouth.
The onset of winter brings frequent cold outbreaks across the central and eastern US that can often result in sudden gale to storm force winds over the Gulf of Tehuantepec. The northerly winds funnel through gaps in the Sierra Madre Mountains and spill out over the Gulf of Tehuantepec and out over the eastern North Pacific.
The Sierra Madre mountains extend southeastward through Mexico and Central America and separates the Gulf of Mexico, the Bay of Campeche´ and Caribbean Sea from the Pacific Ocean. Several mountain gaps allow air to flow across Mexico and the most prominent gap is the Chievela Pass which allows strong cold air surges to pass into the Gulf of Tehuantepec on average about 15 times each winter season with about 2 of these strong enough to reach storm force conditions.
The winds are produced when there is a strong pressure gradient between the Gulf of Mexico to the north and the eastern North Pacific to the south. Northerly winds can increase to storm or even hurricane force during the more extreme events. The first event of each cool season normally occurs in mid-October with the last event occurring in late March or early April.
At the outset of gale events, surface pressures reach a maximum value of about 1028mb at Brownsville and 1024 mb at Coatzacoalcos. During storm events the pressure at Brownsville are about 4 mb higher and at Coatzacoalcos about 3 mb more. During Tehuantepec events, the track of the high pressure center is often more critical than the maximum pressure at the center. The path that the anticyclone takes drives the northerly fetch down the coast of Mexico and setting up the strong pressure gradient across the Isthmus of Tehuantepec.
As a practical matter, whenever the Brownsville pressure exceeds 1020 mb there is a good chance that a Gulf of Tehuantepec event may occur so mariners expecting to pass across the Gulf of Tehuantepec should monitor the surface forecast charts for the Western Gulf of Mexico as an indicator.
During gale events, the center of the high could track as far north as the Tennessee and Ohio River valleys while storm events require the high center to track into Mexico or the western Gulf of Mexico. Storm events are also frequently correlated to strong 500 mb upper level troughs.