| my account | login-logout | resources | classroom help | support | catalog | home | get webcard |

Online Classroom


Post New Topic  New Poll  Post A Reply
search | help desk | commons
  next oldest topic   next newest topic
» Online Classroom   » Marine Weather   » Public Discussion of Marine Weather   » Reading and Writing on Weather Maps - part 6 of 5

   
Author Topic: Reading and Writing on Weather Maps - part 6 of 5
cbassani


 - posted April 08, 2020 07:58 PM      Profile for cbassani           Edit/Delete Post 
Hi. I was trying to calculate the wind velocity based on the definition:

V = (40/(D*sin(Lat)))*0.8

V = (40/(1.7*sin(48.5)))*0.8

On my calculator, using the above order of operations, I get -19.19.
On my computer, following the same order of operations, I get 15.13 (the same as the video).

I am struggling to understand the difference between the two, because I would typically use my phone's calculator for these functions. If I do, I will be incorrect (according to the video). I'm stumped! Any thoughts?

cbassani


 - posted April 08, 2020 08:22 PM      Profile for cbassani           Edit/Delete Post 
Here's an excel version of the same calculation attached - Velocity is calculated at -19.19.

In the video, the reported wind observation was 20 kts and was also pointed in the opposite direction as would have expected based on wind direction from High to Low.

Thanks for any guidance you can provide.

David Burch


 - posted April 08, 2020 09:24 PM      Profile for David Burch           Edit/Delete Post 
You can include an image but not a file.

Your formula is right. surface wind = 0.8 *40/[D*sin(Lat)]

Be sure the angle is set for degrees if using degrees. Some apps like Excel require radians, so you would use sin(48.5*pi()/180) or sin (deg(48.5))

From: Starpath, Seattle, WA
cbassani


 - posted April 09, 2020 12:28 PM      Profile for cbassani           Edit/Delete Post 
I think that helps! What I learned is that both Excel and the calculator on my phone require me to convert degrees of Latitude into Radians as you suggested. Thank you!

The image I've uploaded is a screen capture of the spreadsheet that I've been working on to understand the calculation.




All times are Pacific  
Post New Topic  New Poll  Post A Reply Close Topic    Move Topic    Delete Topic next oldest topic   next newest topic
Hop To:

Starpath School of Navigation

Copyright, 2003-2020, Starpath Corporation

Powered by Infopop Corporation
UBB.classicTM 6.3.1.1