HARLINGEN — The South Texas summer isn’t finished with us just yet.
Weather forecasters have issued a heat alert for the entire Rio Grande Valley from today through Saturday.
Heat indices — the feels-like temperature — will range from 105 to 110 degrees for a few hours each afternoon.
Actual temperatures during the week will range from the mid-90s along the gulf to 105 and higher in the Upper Valley.
In fact, today may turn out to be the hottest day, with temperatures forecast at 98 in Brownsville and along the coast to as high as 108 degrees in the Upper Valley. The break line between the 90s and the 100s will be I-69E/U.S. 77.
“It’s going to be a hot Valley week ahead,” said Matthew Brady, meteorologist with the National Weather Service in Brownsville.
Forecasters say the worst of the potentially-dangerous heat and humidity levels could be today and Wednesday in Hidalgo and Starr counties, with heat indices soaring to between 111 and 113 degrees in the afternoon.
The blame for the searing temperatures is ridging in the mid-levels of the atmosphere which will continue to dominate the week’s weather pattern.
“The heat is due to a ridge of high pressure that is around the mid-levels of the atmosphere, let’s say 15,000 to 20,000 feet up,” Brady said.
“It’s a very dry pattern with very high temperatures, and there’s not going to be much cloud cover,” he added.
The continuation of the hot, dry weather pattern — disrupted briefly last week by the remnants of Hurricane Franklin — is also known as La Canicula, Spanish for the dog star Sirius, which in mid- to -late summer rises in the evenings in the southeastern sky.
La Canicula is caused by a persistent and stable high-pressure system which parks over New Mexico, West Texas and northern Mexico and dominates Valley weather in mid- to late -summer.
Historically it usually ends around Aug. 11, but forecasters concede the date is just an average over the years, and often the weather pattern endures much later into August and even September.
La Canicula delayed its departure until well past Aug. 11 both in 2015 and 2016, forecasters say.
On the plus side, at least for Valley residents, forecasters say La Canicula’s forceful presence is the key factor in driving tropical systems like Hurricane Franklin south of Texas to make landfalls in Mexico.
“In this position, tropical waves or cyclones are ’steered’ well south of the Rio Grande around the periphery of the ridge — most often into Veracruz,” Brownsville forecasters said in a blog post Saturday.
Overnight lows will remain warm, ranging from the upper 70s into the low 80s.
(which impacts heat index)
1. 50 percent humidity is a sponge half full – Humidity describes the amount of water molecules in the air. The amount of moisture the atmosphere can hold depends on the temperature.
2. Big cities stink in summer – we can thank humidity for that – People are better at detecting smells in a humid environment. In heat and high humidity, there are more water molecules in the air to bind and carry odorous particles to your nose.
3. Once upon a time, people measured humidity with hair curls – The first hygrometer to measure humidity was built in 1783 with, you guessed it, hair.
4. Sports and humidity, don’t ’overdew’ it – Humidity can make the difference between a home run and a long fly ball in the game of baseball. Also, exercising in high humidity can be dangerous. The higher the dew point, the less effectively your body cools itself.
5. Humidity is for the bugs, especially moths – It’s the little guy that survives in wet heat. Humidity increases survi-vorship and insects seek moist climates. Moths make the most of the moist and humidity can help moths detect which flowers are high in nectar.