Former Hurricane Carlos, now a strong Tropical Storm, is producing gusty wind and rain in a substantial arc of coastal Mexico.
It is the second storm close enough to the coast to be a threat this season, which began on May 15, and El Niño dictates that more hurricanes, possibly major ones, will threaten the coast from Acapulco to Baja.
El Niño’s Effect On Hurricanes In The Atlantic And Pacific
The enhanced instability over the anomalously warm equatorial Pacific during El Niño creates an undulation in the jet stream. A ridge forms over the eastern Pacific near Mexico, and the low wind shear is a favorable environment for tropical development.
The downstream trough over the Caribbean leads to increasing wind shear across much of the Atlantic Basin, and thus decreased tropical storm activity.
A Seasonal Shift In Hurricane Tracks
Since 1950, twelve hurricanes have made landfall on the Pacific coast of Mexico, five of them major hurricanes.
As the hurricane season winds down in the Atlantic during October, activity shifts to the Caribbean and Gulf of Mexico. In the Pacific, storm tracks change in a dangerous way for the Mexican coast.For most of the summer, upper winds are light and generally easterly over the offshore Mexican waters. Storms tend to drift northwest and die over colder water, though a slight shift in the flow can push a storm such as Carlos ashore.
As the fall pattern sets in, westerlies encroach on the area, and the likelihood of a hurricane being steered to the coast increases.
Of the four category four storms to hit Mexico’s west coast, three made landfall in October. The only category five hurricane made landfall on October 27, 1959.
The Great Hurricane Of 1959
The 1959 Mexico Hurricane (it was before naming of Pacific hurricanes started) moved parallel to the coast as many do. But a trough in the jet stream caused the storm to take a sharp right turn and it slammed into Mazatlan with 160 mile per hour winds.
A Perfect Storm For Perfect Storms
Hurricanes feed off of warm water and develop in regions of light wind shear (change of wind with height). Last summer was characterized by unusually warm water off the southern Mexican coast. The warm water combined with light wind shear due to the developing El Niño to produce 21 named storms in 2014, of which 16 were hurricanes. Most of the hurricanes drifted northwest and died over colder water, but Hurricane Odile struck Cabo San Lucas on the southern tip of Baja California with 125 mile per hour winds and did extensive damage.
This year the warm pool south of Mexico persists, while El Niño has strengthened. The result has already been three named storms. Hurricane Blanca passed within 100 miles of Cabo, but weakened to a modest tropical storm before making landfall in central Baja.
Hurricane Carlos formed, as so many did last year, out of an area of disturbed weather south of Mexico. It took quite a long time to get going, but hurricanes are in no hurry as long as they are over warm water.
Finally Carlos began moving parallel to the coast on Sunday, with top winds flirting with minimum hurricane force of 75 miles per hour. The immediate coastline is being buffeted by strong tropical storm winds, but interaction with the land is keeping a lid on Carlos’s intensification.
Carlos is now a strong tropical storm, but is forecast to briefly regain hurricane strength tonight. As a result, hurricane warnings are posted from Punta San Telmo to Tecpan de Galeana. Carlos will succumb to its proximity to land and begin winding down on Tuesday. However, with such a long stretch of coastline impacted, a fair amount of damage is expected.
By Thursday, Carlos will be just a remnant low pressure center.
The Impacts Of Pacific Hurricanes Don’t End With Landfall
Like all landfalling Pacific storms, even those with little wind, Carlos’s effects will include heavy rain and flooding. Along the coast, five inches will be the norm, but as the rains sweep into the mountains, over ten inches is possible and mudslides are a risk.
The moisture from Carlos will continue north through Mexico and probably reach New Mexico and west Texas by the end of the week. From there, it could enhance rainfall in the plains next weekend.
Mexican Coastal Interests Should Be Prepared
With no end in sight to the favorable conditions for the formation of tropical cyclones south of Mexico, Mexican interests should be especially watchful this summer.
El Niño is expected to strengthen, the water is remaining warm in the breeding ground of these storms, and any nudge from the jet stream could push a storm ashore. October will be a particularly dangerous month as the jet stream shifts southward.