chas
New member
One often hears about the effect of a High Pressure system on the height of the tide. Can anyone quantify the actual effect (ie x millibars = y inches lower)? Does it make a difference of inches or feet?
High Pressure and Tidal Height
- Thread starter chas
- Start date
rogerroger
New member
yes, it can be determined
Tide heights are given for a pressure of 1013 (I think) - and for every mb or 2 above or below the tide is different - I can't remember what the figures are but I'm sure someone will.
I once spent 2 hours on a buoy banging about on the bottom as the tide was 50 cm less than predicted due to high pressure (thankfully it was a charter boat !)
Roger Holden
www.first-magnitude.co.uk
Tide heights are given for a pressure of 1013 (I think) - and for every mb or 2 above or below the tide is different - I can't remember what the figures are but I'm sure someone will.
I once spent 2 hours on a buoy banging about on the bottom as the tide was 50 cm less than predicted due to high pressure (thankfully it was a charter boat !)
Roger Holden
www.first-magnitude.co.uk
DoctorD
New member
From Macmillan Reeds
"a change of 34 millibars can cause a 0.3 metre change in the height of tide."
Tide tables assume average pressure in the local area. Usually 1013 to 1017 mb or thereabouts. Higher pressure is the main issue because it causes lower height of tide.
"a change of 34 millibars can cause a 0.3 metre change in the height of tide."
Tide tables assume average pressure in the local area. Usually 1013 to 1017 mb or thereabouts. Higher pressure is the main issue because it causes lower height of tide.
jimmie
N/A
Re: High Pressure and Wind
Is a force 8 in high pressure more than a F8 in low pressure due to the increased density or weight of the wind?
Is a force 8 in high pressure more than a F8 in low pressure due to the increased density or weight of the wind?
Ohdrat
New member
re F8
Well I think maybe you also take into account the moisture content of the wind as a moist wind I would imagine would be "heavier" and thus increase the force it exerts on your wind guage / sails / hull etc.. possibly the odd bird content too..
Well I think maybe you also take into account the moisture content of the wind as a moist wind I would imagine would be "heavier" and thus increase the force it exerts on your wind guage / sails / hull etc.. possibly the odd bird content too..
G
Guest
Guest
Standard mean is 1013 mb and for every 30 mb = approx. 1 foot ( o.3 mtrs) +/- on tide height, but beware wind direction and speed can also have an effect, especially in esturies. If wind is against main flood it can also hold back the predicted tide height.
NigeCh
New member
Hectopascals
The easiest way to remember it is to think 1 cm difference per millibar taken from 1013 millibars .... But unfortunately millibars are out. The new SI definition for a millibar is a Hectopascal (It's still the same on the barometer .... but scientific committees rule.) .... and then under SI it shouldn't be cm but 10 millimetres!
In old language it's about 1/2" per millibar.
NigeCh
The easiest way to remember it is to think 1 cm difference per millibar taken from 1013 millibars .... But unfortunately millibars are out. The new SI definition for a millibar is a Hectopascal (It's still the same on the barometer .... but scientific committees rule.) .... and then under SI it shouldn't be cm but 10 millimetres!
In old language it's about 1/2" per millibar.
NigeCh
chas
New member
Thanks
Thank you very much for all the information. I move from the boat yard to my mooring on Friday morning - starting with about 6 inches under the keel on one of the highest tides of the year.
Perhaps I had better mount a barometer next to the echo sounder!
Thank you very much for all the information. I move from the boat yard to my mooring on Friday morning - starting with about 6 inches under the keel on one of the highest tides of the year.
Perhaps I had better mount a barometer next to the echo sounder!
jollyjacktar
New member
Tidal Height Good Answers, but.......
Some very good answers to the problem. I can not add any more, except to say that I met a knowledgable mariner once who assured me that [even taking account of tidal differences] sea level in the Irish Sea was a different height than sea level in the English Channel. I'm not too sure how he came to this conclusion but have been pondering matters since then.
Some very good answers to the problem. I can not add any more, except to say that I met a knowledgable mariner once who assured me that [even taking account of tidal differences] sea level in the Irish Sea was a different height than sea level in the English Channel. I'm not too sure how he came to this conclusion but have been pondering matters since then.