Air pressure changes and their meanings

Air pressure in our surrounding world is usually changing all the time and these changes in air pressure may give us precious informations about future developments in our atmosphere, like storms. But not all changes in air pressure are weather depending ! Offshore a rapid movement towards a low pressure area may lead to a sharp drop in air pressure without any information-content for future weather developments. Rhythmic movement of a boat in waters where the tides are high may lead to rythmic air pressure changes > 1 hPa. High waves may influence the behaviour of some barographs. 8,5 m difference in height mean 1 hPa. The precise value of air pressure is much less helpfull than the vaiations of pressure over time. Observing clouds, winddirection, changes in winddirection and changes in windspeed may be more usefull. In tropic region you should observe the regular variations of air pressure (for instance in the trade-wind areas): is this rythm disappearing ? This can be a sign for bad weather.

 This is the typic situation during high pressure periods (perhaps 1025 hPa). The weather is usually stable and fair (In wintertime perhaps foggy). You may observe regular daily variations of the pressure. These waves are depending upon your latitude. During some high-pressure periods you may think for days or even weeks that your barometer is out of order.

for the region of north sea and baltic sea (40 - 60 degrees N) may be valid:

air pressure change / hour air pressure change / 3 hours exspected windspeed (Bft) author(s)
( > + 1,3 hPa )
> + 4 hPa 6 - 7 Kaufeld
( +2 bis +3 hPa ) +6 bis +9 hPa 8 - 9 Kaufeld
( > +3,3 hPa ) +10 hPa
10 oder mehr Kaufeld
-1 bis -2 hPa -3 bis -6 hPa
6 - 7 Karnetzki
> -2 hPa > -6 hPa 8 - 12 Karnetzki

In subtropic and tropic regions some of the above rules may not be valid at all ! In trade wind zones you should observe the daily variations: are they still present ? If not: possible gale is to exspect.

Rapid pressure drop with no or almost no wind: sudden increase of windspeed / gale possible without any other sign ! Weather front with rain coming before wind comes up: stronger winds are exspected. Wind coming before rain: wind will probably not increase.

 some usefull German literature concerning air pressure:

Coles,K Schwerwettersegeln Delius Klasing Verlag
Eyern,P Wetter, Wind und Segeln Nymphenburger Verlag
Herkert,R Wetterkunde für Sportschiffer Busse Verlag
Karnetzki,D Luftdruck und Wetter Delius Klasing Verlag
Karnetzki,D Wolken und Wetter Delius Klasing Verlag
Karnetzki,D Wetterregeln für Segler Delius Klasing Verlag
Kaufeld/Bauer/Dittmer Wetter der Nord- und Ostsee Delius Klasing Verlag
Prügel,H Wetterführer See-Selbstverlag Koch (antiquarisch)
Wiedersich,B Das Wetter dtv

All informations without warranty ! 

air pressure
diurnal rhythm of air pressure