Weather Bell

Michael Lowry

Weather Bell

National Weather Service

Houston meteorologist Matt Lanza recently noted that a city on the upper Texas coast, Galveston, had been setting a staggering number of high temperature records this winter. About one-fourth of the days saw record highs, so Lanza reached out to the local forecast office of the National Weather Service to see if they had any concerns about thermometer calibration or recent land-use changes at Scholes Field in Galveston, where the temperature is recorded. No, he was told, it has just been that "sort of winter."

From the period of November through February, Galveston ended up setting a total of 31 record high temperatures. And it is not like Galveston is a recently thrown-up beach community; the city it has a history that goes back two centuries. It formerly served as the capital of the Republic of Texas, and it has formal meteorological records that date all the way back to 1874.

It wasn't hard to find the culprit for Galveston's heat this winter, as the barrier island's weather is dominated by the Gulf of Mexico. The Gulf has been extremely warm this year. In fact, for the first time on record according to Michael Lowry of The Weather Channel, the daily average surface temperature never fell below 73 degrees Fahrenheit during the just-concluded meteorological winter. It's enough for us to wonder, beyond the climate implications of a steamy Gulf and its impact on temperatures in the southern United States, how might the heat affect storm seasons later in the year?

Tornadoes

For the spring and early-summer storm season in the central and southern US, the warm waters will likely have an effect. While the relationship is far from absolute, scientists have found that when the Gulf of Mexico tends to be warmer than normal, there is more energy for severe storms and tornadoes to form than when the Gulf is cooler.

One of the best predictors of storm activity is a variable known as convective available potential energy, or CAPE, which essentially measures the amount of energy available to rapidly lift a parcel vertically through the atmosphere. (Such lift is essential to bring warm, moist air higher into the atmosphere and create instability). Values of 2,500 joules/kg are generally considered high enough to provide ample energy for severe storms to form.

Last year, atmospheric scientists studied the relationship between CAPE and Gulf of Mexico sea surface temperatures, and they found that warmer conditions in the Gulf leading into and during the spring storm season resulted in a small but significant increase in tornado activity. For some areas of the central and southern United States, CAPE values were about 250 J/kg higher during years with high temperatures than low temperatures.

Given the very warm baseline for Gulf temperatures this spring, some meteorologists are already concerned about the potential for an early and active spring storm season, with warmer, more moist air flowing in off the Gulf of Mexico. However, it bears repeating that the relationship is not absolute—there are still many other ingredients needed for supercells to form, including large, upper-level storm systems spinning down into the central plains from the Rocky Mountains.

Hurricanes

Sea surface temperatures also factor into the formation and strengthening of hurricanes, although hurricane season doesn't formally begin until June 1 and really doesn't get going until late July or August. Typically, waters of about 80° or warmer support hurricanes, so even with the record warmth this winter, it's not like the 74° waters in the Gulf are going to support tropical cyclones any time soon.

But what about later this year? Does exceptionally warm water in winter augur a harsh hurricane season? The short answer is not really, says Phil Klotzbach, an atmospheric scientist at Colorado State University who specializes in seasonal hurricane activity. "They really don't correlate well with Atlantic hurricane activity," he said of winter sea surface temperatures. "I think the primary issue is that Gulf sea surface temperatures are always plenty hot to support major hurricane activity during the season."

Phil Klotzbach

Phil Klotzbach

Rather, Klotzbach told Ars, other factors will be more dominant in determining whether hurricanes ultimately form and intensify in the Gulf this summer. Among those variables, he said, are vertical wind shear and moisture levels in the mid-atmosphere.

Listing image by Eric Bangeman