Warm Gulf adds energy to storms
Spring is the season for severe weather in Central Texas and forecasters are concerned about flooding.
The thunderstorms that started rolling over Central Texas late Monday could be a sign of things to come this spring.
The storms, which were expected to bring deluges of up to 7 inches in some spots before diminishing Tuesday, were fed by moisture from an unusually warm Gulf of Mexico. The Gulf is, in fact, going through its warmest stretch since people began tracking its temperature. That warmth means storms such as the ones that hit Monday will have extra energy — creating more potential for torrential rainfall and the wind-lightning-and-maybe-eventornadoes variety of storms.
“If you give these storms an extra 10 to 15 percent energy, that can be enough” to feed something like a tornado, said Jon Zeitler, the science officer for the National Weather Service office that covers Austin and San Antonio.
But forecasters on Monday afternoon were more concerned about possible flooding around Central Texas than twisters.
Much of the area was under a severe thunderstorm watch for most of Monday night.
Historically speaking, spring is the season for severe weather in Central Texas.
“Large hail, damaging winds, dangerous lightning, tornadoes and flash floods all increase during this time of the year,” Lower Colorado River Authority meteorologist Bob Rose said in a recent video blog entry. The May 2015 floods that ravaged San Marcos and other parts of Hays and Bastrop counties are but one example — and with spring having arrived early this year, Central Texas is well into the season for potentially devastating floods. Expect to hear the public safety man- tra of “Turn Around, Don’t Drown” a lot.
A warmer Gulf, though, does not necessarily mean more storms will form.
Other meteorological phe- nomena, such as temperatures at the equatorial Pacific, have already led forecasters to warn that more flooding and extremely high winds are possible this spring, Zeitler said. The Gulf could give more liveliness to storms that do hit Central Texas, according to meteorologists — who are quick to add that crazy storms are not guaranteed and that forecasting deals in probabilities, not the cer- tainties of people who claim to know the future.
For storms to form, three ingredients are necessary, said Troy Kimmel, a Univer- sity of Texas meteorologist: moisture, rising unstable air and lift (something to provide a nudge).
The Gulf typically provides the moisture for Central Texas storms. The instability usually comes from low-pressure systems that allow warm, high-energy air molecules to rise and churn; these systems tend to flow east from the Chihuahua des- ert, over the border moun- tains and into the American Southwest. The lift often comes from fronts that roll from the West Coast and into the Plains states and Texas.
When those three meteo- rological phenomena meet, storms often form.
Only 5 percent of thunderstorms in Central Texas reach severe status, though, Kimmel said. He said the severe varieties of storms also require, among other ingredients, strong winds high in the sky and atmo- spheric instability “on steroids.”
“Just because you have a lot of moisture doesn’t mean you get more severe weather,” Kimmel said.
But if the other ingredients are in place, a Gulf that is feeding extra energy into storms gives them more potential to create severe weather.
“While the relationship is far from absolute,” weather blogger Eric Berger recently wrote, “scientists have found that when the Gulf of Mexico tends to be warmer than normal, there is more energy for severe storms and torna- does to form than when the Gulf is cooler.”
The storms this week are also occurring against the backdrop of the warmest start to a year in Austin history. That phenomenon is also linked to the warm Gulf temperatures, meteorolo- gists say. Austin is not the only part of Texas experienc- ing weirdly warm weather. From November through February, Galveston set 31 record highs, Berger wrote.
Berger, whose blog entry was based on peer-reviewed academic papers, wrote that warm Gulf temperatures were primarily responsi- ble. The daily average surface temperature of the Gulf did not dip below 73 degrees for the entire winter — the first time that has happened, according to the Weather Channel’s Michael Lowry.
Those conditions could be a fluke, various forecast- ers and climate scientists say. Although one season is not proof of global climate change, the preponderance of evidence strongly suggests that Central Texas is in for hotter, drier and more severe conditions in the coming decades, said UT climate researcher Kerry Cook — including more storms of the variety that could be hitting this spring.
The Gulf warmth has probably also contributed to the unusually high number of tornadoes across the United States. So far this year, Zeitler said, the U.S. has seen nearly four times the typical number of tornadoes.
Tornadoes are uncommon in Central Texas. Still, the region might have already endured two rounds of them: In the overnight hours of Feb. 19-20, two twisters struck in eastern Williamson County and two cut a path in northern Hays County; on April 2 in western Travis County, eyewitnesses said they saw a waterspout form over Lake Travis just west of Austin.
Zeitler said forecasters’ advice about the season would remain the same even if the region seemed to be in for a relatively calm spring. That advice includes having family evacuation plans and knowing where in a house to go if extremely high winds hit. Knowing to head to a hallway or other interior room with no windows could be important.
This year, on May 27, the community of Jarrell in northern Williamson County will mark the 20th anniversary of a tornado that wiped out the Double Creek Estates subdivision, killing 27 people.
“That can have an impact on a community’s outlook for a generation,” Zeitler said.
The storms this week are also occurring against the backdrop of the warmest start to a year in Austin history. That phenomenon is also linked to the warm Gulf temperatures, meteorologists say.