The temperature Thursday in Washington soared to 98 degrees, the hottest so far this summer. The heat index, which factors in humidity, registered 104 degrees.

Get used to it.

An analysis released Wednesday by Climate Central, a nonprofit science communication group based in Princeton, N.J., says these kinds of brutally hot and humid days are becoming more common.

Climate Central’s States at Risk project, featuring an interactive website, not only analyzed historical heat and humidity data to document observed trends but also, using climate models, projected how hot and humid days will evolve into the future.

All data point toward steamier times ahead.

Hot and humid days up substantially since 1970

The District is now sweltering in 95-degree heat on 7.5 more days per year than it did in 1970, Climate Central says. In 1970, D.C. averaged seven or eight 95-degree (or hotter) days in a typical year. Now the number is closer to 15. In the scorching summer of 2012, we had a record-tying 28 such days.

But it’s not just the heat.

Summer dew points, which are an absolute indicator of humidity, have also risen substantially.

In the early 1980s, when Climate Central began its dew-point analysis, the average summer dew point was around 63 degrees in Washington. Now, it’s around 67 degrees.

The increase in dew point has practical implications for how uncomfortable it feels. As the dew point approaches 70 degrees, it becomes noticeably more steamy outside.

Era of sultry summers just getting started

Climate Central projects that the punishing hot and humid days will dramatically increase in frequency in the coming decades.

In Washington, the number of days in which the heat index is predicted to reach at least 105 degrees triples by 2030 and increases by a factor of five by 2050, relative to 2000.

Climate Central calls such days “danger days.” In Washington, danger days (heat index of 105 or higher) equate with the threshold at which the National Weather Service issues heat advisories, as it did Thursday. Under such conditions, heat-related sickness and even deaths become more likely.

“Elevated heat, especially along with high humidity, makes it difficult for the body to cool itself,” Climate Central explains. “In addition to increasing the risk of mortality, heat can cause problems throughout the body. It can range from dehydration, cramps, exhaustion, dizziness, vomiting and heat rash to more serious issues involving kidney failure, heart issues and exacerbation of respiratory issues.”

D.C.’s summer climate to resemble South Texas?

Using projections of summer warming by 2100, Climate Central says D.C.’s climate will, by then, most resemble today’s typical summer environs in Pharr, Texas — a Mexico border town. That is, it projects D.C.’s average summer high temperature to rise from roughly 87 degrees to 97 degrees.

Of course, such projections are based on climate models which assume the emissions of greenhouse gases will continue unabated through the end of the century. If the global community finds ways to cut emissions, the warming would not be this steep. Also, if the climate is less sensitive to increases in greenhouse gases than assumed by these models, the warming would be less.

But, observed data make it clear the D.C. area is on a warming trajectory.

Climate Central’s analysis documents similar trends in hundreds of metro areas across the Lower 48. “Using several measures, our findings show that most U.S. cities have already experienced large increases in extreme summer heat and absolute humidity, which together can cause serious heat-related health problems,” the analysis states.