Apologies for straying a bit off-course ...

As others mentioned, weather/climate conditions are one of many factors affecting perceived pack-weight.

Somewhat simplistic, but everybody's probably familiar with the so-called "heat index" that combines temperature and humidity to produce a "feels like" temperature. Using the chart, your 93F/78% humidity produces a heat index of 123F (nearly in the "extreme danger" of heat disorder), whereas my 102F/30% humidity is around 104F (still nasty by any standards!).

Accuweather.com's "RealFeel Temperature" index is more useful ... factors in "the effects of temperature, wind, humidity, sunshine intensity, cloudiness, precipitation and elevation on the human body."