The heat marches on... but we are a little held back with the heat index values today compared to yesterday. For most of us, at least as of the 2:00 hour, heat index values are holding under 105 degrees, but they are still hot enough. Showers and thunderstorms are staying off to the southeast today, but hit-or-miss thunderstorms will be working back into our forecast for the rest of the work week. Because of the high heat index values and the sultry overnight temperatures continuing, the Heat Advisory for our area has been extended through Wednesday evening, and it may need to be extended further through the week.
We stay partly cloudy to mostly clear as the head into the evening hours. Notice that many of us are still above 89 or 90 degrees as we head toward sunset. With dewpoints well into the 70s, we won't be cooling off quickly, and we look to only make it down to the mid 70s toward daybreak Wednesday morning. We once again head for the mid 90s on Wednesday, but Futurecast is picking up on the idea of a few isolated showers and storms across northern Alabama during the evening hours. There has been disagreement on how widespread this will be and where exactly it will set up, but this is a sign that rain chances are returning.
Scattered hit or miss thunderstorms look to continue in the forecast Thursday and Friday, before a weak frontal boundary brings slightly cooler and somewhat drier air into the area for the weekend. As of now, all the storm activity looks scattered, but we're into the time of year where thunderstorm complexes don't get handled well in advance by the models, and we will be watching Friday night as that front moves in just in case thunderstorms end up being a bit more widespread.
The heat hangs around through Friday before we take a step down with afternoon temps for the weekend. Highs Saturday and Sunday might be as low as the upper 80s over southern Tennessee and in the lower 90s over north Alabama. That's not too much cooler than what we have now, but drier air will be moving in as well, and that lower humidity will mean those upper 80s and lower 90s for the weekend will be much more tolerable and not nearly as dangerous.
The break is short-lived though as the upper-level ridge over us this week builds back overhead next week after the weekend front shifting it west. That upper ridge means subsidence aloft, sinking air. That puts a lid on thunderstorms, on widespread clouds, and that sinking air is also warming air. We look to be hot next week as well, and temperatures by the middle of next week MIGHT be a little warmer than anything we're seeing this week!
We are watching a tropical disturbance off the coast of Nicaragua and Costa Rica in the western Caribbean. The National Hurricane Center gives it a 40% chance of developing into a tropical depression or stronger over the next 5 days. Should the system develop, it looks like it would head northwestward across the Yucatan and into the Bay of Campeche and southwestern Gulf before possibly moving into Mexico. This does not look to be a threat to the United States, and we don't see any reliable data that suggests a tropical threat to the United States for at least the next 5 to 7 days.