Jun 11, 2013 9:27 AM by Dave Baker

When Are Heat Advisories Issued?

In South Louisiana, heat is as common as mosquitoes.  Summer is the season we love to hate.  In Lafayette the normal high temperature is above 90 degrees from June 3rd to September 12th or about 1/4 of the year.  We love to hate heat and mosquitoes almost as much as we love to hate humidity, because after all, humidity makes it feel much worse!

Today the forecast calls for temperatures around 92 degrees with a heat index of 98.  By the end of the week we'll go with temps around 95 and a heat index around 105.  The heat index is a measure of how hot it really feels because of high humidity.  

The higher the humidity, the longer it takes for water to evaporate.  Sweating produces moisture on your skin and when it evaporates, it cools you.  When the air is dry you might not notice you're sweating because the sweat evaporates from your skin almost instantly.  More likely you're used to your skin, clothes, hair and everything else soaked with your sweat because the air is already saturated with so much moisture, it doesn't need any more from you.  No evaporation means no cooling..and no cooling means more complaints to the weather department.

Occasionally the heat index gets to a level where it can be dangerous so a heat advisory may be issued.  In Louisiana a heat advisory is issued when the heat index is expected to be between 105 and 110 degrees for at least three hours, and/or when the night time temperature remains above 80 degrees.  But "heat advisory" heat is different in other parts of the country.

Minnesota issues a heat advisory when the heat index is expected to reach 100 or when the actual temp is 95.  We'd have a heat advisory every day here.  In Washington DC the advisory is issued when the heat index is expected to be over 105 (no time limit).  In New York city a heat advisory is issued when the heat index reaches a mere 95!  Boston uses the same criteria as NYC, but get this...a "Heat Wave" is defined in Boston as two consecutive days of 90 degrees or higher.  Ha!  Bostonians would never make it on the Gulf Coast considering we had 81 days over 90 in 2012 (Average is about 100) and 20-30 in a row isn't uncommon.

It's all relative.  Remember they laugh at us when we're shivering in winter when the high is below 60!  Be safe this summer!


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