Extreme heat roasts Texas, Gulf coastal states

• The heat that has plagued the region all summer has abated somewhat in southern Louisiana. But the entire Gulf Coast has seen a hotter than average season so far, and with Gulf of Mexico waters spiking to record highs, any cooldown may not last.

The big picture: Heat warnings and advisories are in effect for some of Texas' biggest cities, from Austin to San Antonio and Houston, with relief in the form of less humid and searing heat coming toward the end of the week.

• The heat has tested the Texas electrical grid, but with increased solar power capacity and battery storage to add electricity once the sun goes down, the grid has so far been stable.
• The big danger is to human health, with the Houston Metro area, San Antonio and Austin ranked as in the extreme heat risk category on Wednesday and Thursday too.
• According to the NWS, during such combinations of heat and humidity, "Impacts [are] likely in most health systems, heat-sensitive industries and infrastructure."
• The heat is an acute public health threat, particularly for any outdoor workers, those with underlying health conditions and anyone without adequate access to cooling.

What they're saying: The National Weather Service forecast office in Houston-Galveston sounded the alarm for highs of 103°F to 105°F, and heat indices above 110°F in a technical forecast discussion on Wednesday morning.

• "There's only so many ways a forecaster can write "it`s going to be
  hot." ...and I have run out of ways," an NWS forecaster stated, referencing the duration of the extreme heat.
• Forecasters noted that an upper level high pressure area, also known as a heat dome, has been stuck in place, pumping hot and humid air into much of Texas. But it will finally budge on Thursday, allowing temperatures to drop into the upper 90s.
• The high temperature in Houston reached 102°F on Tuesday.

Threat level: Forecasters warned of the potentially deadly consequences of the heat through Thursday. "These are DANGEROUS Heat Conditions," they wrote. "It is very important to make the proper adjustments to keep yourself, loved ones, and pets safe from the heat. Significant impacts from heat can occur faster than you expect."

Context: Climate change is making heat waves far more likely to occur, as well as more severe and longer lasting.

• This is having increasingly deadly consequences in the U.S. and around the world as temperatures spike to levels humans and their built infrastructure have difficulty tolerating.

By the numbers: The forecast high temperature for Wednesday in Houston is 101°F, with heat indices of about 110°F. In some spots, the heat index, which measures the heat plus humidity, is likely to be closer to 115°F.

• Houston's is not forecast to fall below 97°F for a high through Friday, however. In fact, most of Texas can expect above average temperatures this week, but the hottest days will end for most at the end of the work week.

• In New Orleans, which has had its share of stifling heat this summer, temperatures have moderated, but only into the upper 90s.
• Looking at the summer so far, Houston is tracking towards its fifth-hottest summer on record, while New Orleans is having its second-hottest summer so far.
• Parts of Florida — including Lakeland, Orlando and Tallahassee, are seeing their hottest summers. In Miami, it will likely be a top 10 hottest summer. (Meteorological summer ends on August 31.)

Zoom out: One factor contributing to the extreme heat throughout the Gulf Coastal region is the unusually hot Gulf of Mexico, which has surpassed record highs for this time of year, as measured via a metric known as ocean heat content.

• According to Climate Central's new Climate Shift Index: Ocean, which seeks to attribute ocean temperatures to climate change on a daily basis, long-term, human-caused warming is raising the likelihood of such hot waters in parts of the Gulf of Mexico by up to 500%.
• Winds blowing onto the coast from the warm Gulf prevents the air from cooling below the upper 80s°F overnight.

Storms can tap moisture from the Gulf and drench areas far to the north, as occurred over the weekend in Connecticut and Long Island, with largely unpredicted, deadly flash flooding.

• The rainfall amounts there had just a 0.1% chance of occurring in any given year, otherwise known as a "1,000-year" event.

What's next: A cooldown for the Midwest and East Coast will continue into the weekend, but outlooks for the rest of August show high odds of warmer-than-average temperatures across most of the Lower 48 states, including the Gulf Coast.