Archive for the ‘Wind force’ 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 FORCE OF WIND – A GREAT SURPRISE FOR MOST PEOPLE

Moving along under a light breeze - working upwind with sails sheeted in close.

Please left-click this image for enlargement.

In order to changes gears for a moment, I’ve inserted a photo of a form of travel, recreation, and sport that utilizes the wind.  The image above is of my little sloop, Nature’s Way.  It was taken by my wife from a position onshore.  The craft has a fixed shoal draft keel that accounts for one-third of the weight (displacement) of the craft (1,100 pounds).  In spite of the keel, she is very easy to launch from the trailer and also easy to retrieve – pretty much a one-person job.  I wish for everyone that they could experience such peace as is provided by sailing in fair weather.  However, experienced sailors know that when the wind picks up, the force from it increases exponentially.  If they don’t know that fact and the wind velocity increases more quickly than they anticipate they are likely to some day find themselves in a position where they have waited too long to reduce the sail area.  Then they will have their hands full – especially if sailing solo.

This image shows the craft moving 45° “off the wind.”  In other words, under skillful hands the boat is being “pulled” as well as pushed by the wind in a general upwind direction.  Most sailboats with this type of rig can sail 45° off the wind but no closer than that.  However, by zig-zagging from one tack point to the other, the boat can reach an upwind objective.  It reminds me of working upslope on a mountain trail by taking a switchback route, rather than climbing directly upward.  SO, DON’T THINK THAT SAILBOATS ONLY SAIL IN THE GENERAL DIRECTION OF THE WIND – THEY CAN ALSO SAIL IN A GENERAL UPWIND DIRECTION AS IS BEING DONE IN THIS IMAGE (though there is about a 90° degree arc – 45° degrees on either side of the wind-line that they can’t sail effectively).  To be thorough I must add that some extremely well-designed boats with well-cut sails can get closer to the wind with a skillful skipper.

A sailboat can also sail nicely broadside to the wind.  That position is called a beam reach.  In time, for those of you who are interested, I will probably post a little tutorial on the points of sailing.  For now, I hope the image below with some elaborations will whet your appetite.  To reach it you must click the enticement to read on when you reach it at the end of the next paragraph.  Now – LET’S DISCUSS THE POWER OF A STORM’S WIND OR ANY OTHER WIND ACCORDING TO ITS VELOCITY:

There are some widespread misconceptions about the relationship between the wind’s velocity and the force it is able to exert.  Doubling the wind velocity quadruples the air’s potential force upon a surface that it strikes at right angles.  Early on in my teaching career it because quite apparent to me that most people assume that doubling the velocity simply doubles the force.  But that is far from true.  For example, a 110 mph wind has 4 times the potential force of a 55 mph wind! Continue reading

Hurricane Ike – Where Is He Going? No One Knows!

Though Hanna is a concern these days, it appears that Ike is going to be much more powerful.  Perhaps in 5 days we will know what he’s going to do but right now there are significant differences of “opinion” among the models and, I presume, among the forecasters.  One “take” is that Ike will veer at some point and stay in the Atlantic, maybe posing a substantial threat on the East Coast all the way from Florida up.  The other “take” is that he could slip into the Gulf of Mexico, at which time the West Coast of Florida and other Gulf Coast states could get a big one.

This afternoon Ike’s winds have been sustained around 140 mph – a Cat 4.  This hurricane is a classic Cape Verde type and not one to be casually regarded.  I urge you to read Dr. Jeff Masters’ assessment of Ike in his posting this morning.  If it no longer appears you can find it archived at the site.

http://www.wunderground.com/tropical/

There are some widespread misconceptions about the relationship between the wind’s velocity and the force it is able to exert. Continue reading