"WARM" or "HOT" ?

Today, some cooler weather is (finalkly) bringing some relief from the heat that has been grasping the Midwest and the East coast here in the U.S.. As I’ve traveling east, it seems I’ve been following the heat-wave and that has made life a bit less... fun .

Yet I am puzzled by some American English usage here; when I landed in Baltimore, the flight attendant said: “It is quite warm out there today – 98°F (37°C),” which made me jump, “What? “98°… quite WARM?! ... so when excatly does it ever get HOT for you lady?”.

In fact, I have been noticing that many people say “WARM” when I think “HOT”. I’d say something like “It’s hot today” to which people would say, “Yes, it’s quite warm”. So they agree with me but use “quite warm”. Is it the same to them?

When I checked the dictionary though, it seems there is a difference :

• WARM = “somewhat hotter than temperate; having or producing a comfortable and agreeable degree of heat; moderately hot”

• HOT = “being at a high temperature.” – not necessarily boiling, just a “high temperature”.
  

I imagine that the whole idea of a heat-wave is that it brings "high temperatures”. Interestingly, while some newspapers talk about the danger of the hot weather , others say it was the warmest temperatures [in a long time..]. Why not “the hottest” temperatures?

I’ve been trying to figure it out but it’s still very confusing. My theory has been that the use of “warm” is either ironic – in tongue and cheek manner, or that it just makes it sound better and more bearable. The other possibility of course is that some people use it indiscriminately because they don’t know the difference.