Good evening from chief meteorologist Tony Petrarca..
A noticeable rise in the humidity levels Today which helped to fuel some scattered downpours. Dew points right now are well into the 70s indicating lots of moisture in the air. This high humidity will stick around thru the weekend, but starting tomorrow it will be accompanied with heat, as afternoon high temperatures soar into to the lower 90s inland.
The combination of heat and humidity makes it feel hotter and this is known as the heat index. It’s what the temperature feels like to the human body. Heat Index values on Thursday (and possibly Friday thru Saturday) will approach 100 degrees away from the ocean
Forecast Heat Index values Thursday 3PM..
When our body gets too hot we begin to perspire (sweat). When perspiration evaporates from our skin, that process actually has a cooling effect, reducing surface body temperature. However when its very humid, like right now, that evaporation process decreases and thus less cooling. This is the reason why we feel a bit of a chill getting out of a pool or the ocean when there is a dry breeze. The water on our skin evaporates quickly with drier air.
A Heat Advisory is in effect Thursday for areas shaded in orange. A heat advisory is issued if the “feel like” temperatures are expected to reach a minimum of 100 degrees for two consecutive hours. The highest chances for that to happen will be across inland areas away from the coast.
Bottom line..high humidity means less evaporation from our skin and no cooling effects….we feel hotter.
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Source – http://wpri.com/blog/2016/08/10/heat-advisory-issued-for-thursday/