Archive for the ‘Hurricane winds’ Tag

HURRICANE MISCONCEPTIONS – A LIST OF 23

Image source of Ike radar loop = WeatherUnderground.com

Image source of Ike radar loop = Weather Underground

LEFT CLICK IMAGE TO ENLARGE AND SEE A RADAR LOOP OF IKE AS HE COMES INTO VIEW AND EVENTUALLY MAKES LANDFALL.  WATCH FOR A DISTINCT RIGHT TURN TRACKING DIRECTLY TOWARD HOUSTON JUST BEFORE REACHING THE COAST.  IF IT HAD CONTINUED STRAIGHT, THE WINDS AND THE SURGE ALONG THE COAST AT GALVESTON AND SOUTHWESTWARD WOULD HAVE BEEN EVEN WORSE BECAUSE THAT COAST WOULD HAVE BEEN CROSSED BY THE RIGHT-HAND LEADING QUADRANT OF THE STORM

(see item 13 below).

23 COMMON MISCONCEPTIONS ABOUT HURRICANES

©* Tonie Ansel Toney (see conditions for copying at the end)

https://cloudman23.wordpress.com/

I have learned of these misconceptions by communicating through the years with my students, friends, neighbors, attendees of some of the hurricane seminars that I have conducted and visitors to hurricane expos where I have given presentations.  Most of this occurred in Florida.  I learned that these items have been relatively “common” misconceptions through informal pre-tests I have given to college students at the beginning of certain semesters, answers to questions I have asked in classes during the course of myriad semesters, through conversations with people of all walks of life (and a broad range of ages and experience), and by listening carefully.

ALL 23 UPPER CASE STATEMENTS ARE FALSE IN SOME WAY.  BRIEF EXPLANATIONS FOLLOW.

1. IF THE SPEED OF WIND BLOWING DIRECTLY INTO THE SIDE OF A DWELLING CHANGES FROM 40 MPH TO 80 MPH, THE FORCE THAT IT EXERTS INTO THE STRUCTURE WILL INCREASE TO TWICE WHAT IT WAS. THE TRUTH: A doubling of the velocity will cause a four-fold increase of the force upon a surface being struck at right angles.  The relationship is “exponential,” not “linear.”

2. IF, DURING A HURRICANE, YOUR TRUE WIND DIRECTION IS FROM THE SOUTH, THE HURRICANE’S EYE IS TO THE NORTH OF YOU. THE TRUTH:  It is generally west of you.  Hurricane winds move approximately parallel to (or concentric with) the nearly circular eye-wall.  A good rule-of-thumb for eye location (in the Northern Hemisphere) is: Imagine standing with the wind at your back.  Extend your left arm out from your side and your hand will be pointing toward the eye.

3. IF AN APPROACHING HURRICANE IS ABOUT ONE DAY AWAY, PRUNING OF TREES IS ADVISABLE. THE TRUTH:  It is too late to prune at that time – it should have been done much sooner, preferably prior to the hurricane season.  Pruned material must be disposed of properly – if lying around the items can become a dangerous airborne hazards. Please read on by clicking here; there are 20 more which might interest you. And, don’t miss viewing the animated image of Ike at the beginning of this post.

The Effect of Hurricane Winds Upon a House

Image courtesy of NOAA

Image courtesy of NOAA

What follows is an excerpt from a 1998 publication titled AMERICA’S HURRICANE THREAT under the auspices of the South Carolina Sea Grant Consortium.  What I’m showing you is a small part of their sobering account of what can happen to houses in the strong winds of a hurricane.  The house on the left in the image above is mildly damaged compared to many in that neighborhood.  I have been reading the above-mentioned report tonight due to my special interest in Hurricane Andrew.  Those of you who have been following this web-log since its beginning 18 days ago might recall having read somewhere that our home was a total loss in that 1992 hurricane.  In time, I have written about the experience in a recent posting dealing with window protection.  Here is the excerpt from the report:

“Andrew totally destroyed 63,000 homes and partly damaged another 110,000, making 250,000 people homeless. With roofs damaged or blown off, rain following the hurricane poured inside structures, soaking and collapsing Sheetrock and destroying billions of dollars worth of furniture, carpeting, televisions, and other items. The insurance industry estimates that 25-40% of insured losses were due to slipshod construction practices.

Most homeowners do not give a second thought to their roofs-until they leak or disappear. Yet roofs are the Achilles heel of homes in hurricane-prone areas from Maine to Texas.

As strong winds strike a building, their flow is diverted, swirling over and around the structure. Think of a mountain stream roaring against a giant boulder, which deflects the current. The stream flow accelerates around the obstacle, resulting in rapids. In the same way, hurricane winds speed up around corners and edges, creating suction that pulls on building materials like a super-powerful vacuum hose. Fierce gusts and suction pressure make a dangerous combination, especially for roofs. They yank off tiles and shingles, first at the roof edge and then along its slope as you’d peel an orange. During Andrew, huge numbers of tiles were stripped from roofs this way, and carried off by high winds, they crashed through windows by tens of thousands.

If you lose a window or door during a hurricane, you’re in big trouble. Extreme winds push through an opening in a building, increasing air pressure inside like blowing up a balloon beyond its capacity. If you force enough air pressure inside a house, it can break at its weakest point, usually the roof.

As roofs are being pushed off from within, they are being pried loose from the outside. Peel away tiles or shingles and you’ll find a covering of roofing paper, under which is plywood attached to rafters. But a roof won’t stand much of a chance in hurricane-force winds if builders haphazardly tie down plywood to rafters-if they use too few nails or miss the rafters altogether with their nail ‘guns.’ After Andrew, engineers reported that many contractors had routinely missed their marks. ‘With the use of automatic nail guns, the workman lost his feel for the nailing process,’ said Saffir. ‘The result was that many nails went through the sheathing into thin air, not into the truss or rafter below. This was a common occurrence.’

If your plywood sheeting flies away in the wind, you’ve lost more than just a roof covering. You’ve also lost a portion of the house’s structural integrity. That is, plywood sheets are often the sole lateral bracing for the rafters, actually holding the roof together. So with the plywood gone, the rafters are loosely tethered in the wind.

To compound the problem, many contractors fail to tightly fasten wood gable ends-the flat ends of a pitched roof-to walls. So when a powerful gust hits an unbraced gable, the gable end can be pulled loose at the wall, allowing wind to enter the building. If the roof sheathing is pulled off at the gable end, the rafters can fall over.

During hurricane Andrew, tens of thousands of homes were damaged due to such failures in roofs.”

NOTE FROM CLOUDMAN23:  Many of you reading this could be living in dwellings without adequate roof truss tie-downs and/or with poor roof sheathing attachment.  Do you know what the codes were when your house was built?  Do you feel confident that your dwelling was built according to code?  Were the inspections thorough and particular or were they inadequate?  For some, those are hard questions to answer.  In any event, please evacuate if Ike is heading your way.  Heed the warnings.  Please.

Please visit the rest of this web-log at https://cloudman23.wordpress.com/.  If you are interested in weather, there are some tutorials scattered about and more will be added in time.  At the end of this page there is a cue to click to the previous page or the next page.