Sorry your plant is now entirely dead. Rhododendrons must have a moist yet well aerated, acidic soil that drains freely and is not baked by the sun. It looks likely that a lack of one or more of these factors being present has resulted in failure.

I tried to amend the soil but clearly it didn't work. Thank you for your response!

"with temps being 98F for a week or two with no rain, swinging down to 70 and flash flooding."

Root rot of a known, scientifically tested as root rot-sensitive variety that for the most part, should not be marketed on the east coast at all. Even in Michigan, obviously, if they can have that kind of weather. Years ago I saw that there is some idiot on facebook recommending this cultivar for the midwest, but I forget who it was. Some PNW wholesaler I'd never heard of.

"I tried to amend the soil but clearly it didn't work." For future reference to anyone else, doing this would definitely have made matters worse. In plain, sandy acid soil, it might have survived. (assuming that is what you have in your area...some parts of MI are famous for it)

With a very small handful of exceptions, all rhododendrons are susceptable to phytophthora root infections of various sorts given the right conditions: hot, overly damp soil with less than perfect drainage. Yellow flowered varieties are extremely sensitive, but with a couple of weeks of temperatures in the upper 90's accompanied by drenching rains, any variety is at risk. In recent years, root rots have become far more of a problem for me in coastal Maine than they ever used to be. Hotter summer temperatures have raised soil temperatures to the point where phytophthora and other infections have become much more active and lethal than ever before.

This particular Nova Zembla may indeed be dead or very near so, but it may also be suffering from boytriosphaeria stem dieback rather than an infection of the entire root system. Try pruning out the obviously dead part and hope that the plant can regrow and recover. With a vigorous variety like NZ it is at least possible. NZ is also, btw, the only variety of red rhododendron I've seen at the big box stores in many years.

Yes but they vary a great deal. This study puts 'Nova Zembla' in the fully susceptible category, albeit not as bad as some others: https://web.archive.org/web/20151220161750/http://www.holdenarb.org/education/documents/krebs-wilson2002.pdf 

I don't think any plants in that category should be promoted outside the coastal northeast or PNW as mass-marketed plants. Especially, as you say, with high summer temps becoming more common. It's different if Rarefind wants to sell them. That big box stores and their wholesalers do something is neither here nor there. A bad idea is a bad idea.

"but with a couple of weeks of temperatures in the upper 90's accompanied by drenching rains, any variety is at risk."

Well the Southgates and previous non-patented R. hyperythum hybrids, bred in Louisiana, seem to tolerate these conditions just fine. Assuming they are in reasonably well drained soil. I actually have mixed feelings about them though. If they become gas station plants throughout the southeastern US, seems to increase the likelihood of further evolution of pathogens to attack them. Will hopefully never happen. I'm using those as rootstocks for PNW cultivars.

Thank you everyone for responding! That is what I get for purchasing a plant from Lowe's. I am going to prune back the very dead parts and hope for the best.

It looks like it dried out. Even some of the coleus leaves are wilted. Keep it watered in dry weather.