Jul 14, 2011

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It is July, and of course with the arrival of mid summer comes the heat and humidity across much of the US (Especially from the Plains eastward). When it is hot and humid you will often hear meteorologists refer to the heat index.  The heat index simply put is the temperature perceived by your body due to the combo of heat and humidity. For example if is 95 degrees outside and the heat index is 103, your body “thinks” it is 103 and that is how it will behave. With this in mind the summer of 2011 has seen these numbers over 115  in portions of the Plains through South on a few occasions in recent weeks. So is that the worst it can get?  The answer: Not by a long shot.

Looking at recent history the heat index reached as high as 124 degrees in Mt. Pleasant, SC  just this week! At these temperatures any prolonged exposure is dangerous and could potentially lead to heat stroke.  This however is still a long way from the top in terms of observed values.  Millington, TN on August 3rd, 2010 reached a heat index of 130!  This is essentially a life threatening level where heat stroke will occur very quickly.  While it is not often these values are experienced in the US it is still not even close to the world’s highest. For that we must look to the Middle East.

In particular one must look to Dhahran, Saudi Arabia on July 8th, 2003.  Dhahran is a city in the Eastern portion of the country very close to the Persian Gulf. It is the administrative center for the Saudi oil industry. The heat index on that day reach an incredible 172 degrees! For anyone outside this would be deadly very quickly!  When this recorded the actual surface temperature was 108 degrees with an off the charts dewpoint of 95!  It is by way of the Persian Gulf  that this kind of humidity finds its way into the desert in this portion of the world. The surface water temperatures are too high to generate a real cooling effect (sea breeze) so instead they just provide a moisture source resulting in very humid  summer conditions.  Heat indicies in the 130-145 range are not uncommon! It may help to give this some thought the next time your area is slated for a heatwave. Either way be sure to follow common sense when it gets hot and do all you can to stay cool and hydrated!

Sources:

Extreme Weather a Guide & Record Book – By Christopher C. Burt, Mark Stroud

NOAA

Charleston Post Courier