[joe bartels]

NEW YORK (AP) - Americans withered under yet another day of searing sun Friday as a heat wave spread in earnest into the urban core of the Northeast, while warnings about excessive heat stretched from Kansas to Maine and the Carolinas.

Temperatures were forecast near or into the triple digits Friday and into the weekend.

The high temperatures and smothering humidity will force up the heat indexes. Boston's 99 degrees on Friday could feel like 105 degrees; Philadelphia's 102 degrees like 114 degrees and Washington, D.C.'s 103 degrees could seem like 116.

So if 103 and x percentage of humidity feels like 116, then it feels like a 116 at what percentage of humidity? Are they saying at zero or x?

I can hike in 116 and 5% humidity for a couple hours without issue but 103 and 40% will mess with the mind

[Jim_H]

I never believed in the accuracy of Heat Indexes. Since it is a "feels like" index, it is all based on qualitative and therefore shaky data, if it is even based on any data. Maybe 90 F with 50% and 95 F with 40% can relate to each other through some higher numbers on a "feels like" index, but I keep hearing about indexes of 110 in city X on the east coast and I think "110 in the Canyon was nice, what are they complaining about?". Sure, 110 in 10% humidity is pretty nice, but it won't actually be 110 in these cities and 99 with 50% humidity won't feel anything like it did in the canyon. Water condensing on the skin feels nothing like water vaporizing from skin, and that is and will always be the problem with an attempt to arrive at what humidity feels like in a thermo sense. The sensation of the affects of water on the skin is not the same as an actual temperature, so in essence, it's comparing apples to oranges. What they need, what most of the horribly humid world needs (and Arizona on a monsoon day) is a Disgusting Index. An index that incorporates temperature and humidity to arrive at a non-temperature based number, perhaps on a 1 to 10 scale, or maybe even color coded, that gives people something to report on that doesn't cheapen or pervert an actual temperature of 110.

In Medford, NJ today, the forecast high is 101, and humidity will be about 46%, so the disgusting index can be a 7 or 8 out of 10. It is currently 99 with 48%, dew point 76 degrees, but the claimed heat index is 114. I guarantee you that it is nothing like 114 in Phoenix.

I remember being in 60% humidity on a 88 degree day, and that is about as nasty as it gets for me. It would be a 9 or 10/10. White skies, puffy clouds with no blue visible at all, so humid that you're drenched in sweat just sitting in the shade..

[johnlp]

DC is currently 101 feels like 117 at 46% humidity and 77 degrees dew point. Seems like it might by a bit excessive on the "feels like" number.

[trekkin gecko]

dew points in the 70s are miserable
i don't miss that at all (NE)
i'll take our high temps and low humidity any day
but i agree that 101 with high humidity doesn't compare to an actual 117 degree day
it's just mighty uncomfortable

[Trishness]

Being a native of New England I can tell you that NOTHING is worse than dew points in the 70's and humidity over 60%.....well OK there is something worse. I lived in the "Sauna State" (not the Sunshine State) AKA Florida for 3 years. Summers were beyond miserable....temps around 102-105 with 90% humidity. The air was so heavy it was oppressive. Give me 115 in Phoenix any day of the week.

[Nighthiker]

Rather hike in a pizza oven than a sauna.

[RangerKelly]

Out in the midwest and eastern US anything over 90 degrees with a high humidity is absolutely miserable, while I can hike in the desert at 110 degrees relatively easy.

[gsp416dre]

Here in south GA it regularly gets to 100 with humidity in the 80% and up. I have seen it in the high 90's and 95% + humidity. As Rangerkelly put it, it is ABSOLUTELY MISERABLE!! I thought I was gonna die when I left Yuma in the summer at 117 one day to move home to GA and found it at 95 degrees and 90% humidity!! Give me the desert any day in the summer over the "steambox south" summer. You can breathe! And on top of that, your body can actually do its job some there when you sweat, you can sweat here, but it don't do any good, no evaporative cooling going on! I was always fine in Yuma as long as I was drinking water and had it available. Here in GA, I can drink all the water I want and sweat all I want, it doesnt help much.

The heat index idea is not too accurate as to the "what it feels like" idea. 115 in the Sonoran is much better feeling than a "heat index" of 115 in the Swamp!!

[chumley]

There's a lot to be said for your body being used to something too. A few weeks ago, straight out of the desert, I was hiking in 70F and 95% humidity. I was absolutely soaked through. Then it started to rain. Despite my layers and the relative warmth, suddenly I was freezing cold. The next couple of days I had to fight through a cold. My body wasn't used to the humidity and I didn't correctly prepare to deal with it. I think it's more common for people to have poor reactions when coming to a hot-dry climate, but I certainly agree that the Heat Index is a poor scale on which to explain the effect on people. Then again, we're all different!

[gsp416dre]

I would have to agree with you on that one Chumley. I do think though that if people would take proper precautions, they would be better off when going from one climate to the other. I remember when I first reported to the MCAS in Yuma, the emphasis was to hydrate much and often. The heat wasn't as big of a problem for me then, but I did find it very easy to get dehydrated. (Going back to Georgia was a little tougher to get adjusted to.) Unfortunately, alot of folks going to an arrid area from a humid one, tend to not drink as much water because they don't realize they are sweating, even with a relatively small change in temp. Of course, dehydration is a problem in all areas, but seems that in a humid place folks notice sweat and they realize they need to drink more water. But, all in all, I think it doesn't matter where you are, a drastic change in climate can take a heavy toll on you whether it be temp. or humidity.

[Canyonram]

Website with a good description of the Heat Index. Some downloadable spread sheets and pinwheel calculators at the very bottom. The charts include rationale why one Temp + Relative Humidity combination is rated one way while a different Temp + Relative Humidity gets a lower (or higher) danger rating.

http://www.srh.noaa.gov/jetstream/global/hi.htm

If you really want to take your own relative humidity readings, you'll need a sling psychrometer. This unit has a 'wet' bulb thermometer and a 'dry' bulb thermometer. You soak the cotton at the end of the wet bulb in distilled water. The fun part is then slinging the unit to allow the water to evaporate off the end of the wet bulb. If there is a lot of moisture already in the air, less will evaporate off the wet bulb. If the air is dry, more. Like an old fashion slide rule, you then compare the dry and wet bulb temps and can calculate the relative humidity. This unit is used in public health situations to determine the comfort level inside nursing homes,hospitals, apartment buildings, etc. It is used on the athletic field to monitor athletes and fluid intake, etc.

http://www.usatoday.com/weather/wsling.htm

Using a sling psychrometer on the football field:
http://www.youtube.com/watch?v=m1JV3oeEnWg

Instructions to make your own (good science project or something to do instead of yardwork around the house):

http://www.nasa.gov/centers/langley/pdf ... h11.r3.pdf
http://www.flinnsci.com/Documents/demoP ... S10301.pdf