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.

• static air pressure: 

 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.

• increasing air pressure: here is the question: how rapid is the pressure increasing ? A slow and constand increase is a sign for an improvement of the weatherconditions, maybe for a longer time. A rapid incease ( more than 1 hPa/hour ) is instead a sign for a shorter period of better weather and can be a sign for strong winds ("high pressure storm") lasting perhaps several days. Example: a low is going away and the next is following soon after. Constant rapid pressure increase is offshore often a sign for strong winds. 
  

• air pressure is falling: the question is: how quick is the pressure falling per hour (per three hours)? And is the tendency constant or is the pressure-drop increasing ? A slow constant decrease of air pressure is a sign for a slow worsening of weatherconditions, mostly at the end of a high-pressure period. At the beginning the pressure decrease may be difficult to discover. Some variations (waves) may be seen. A rapid fall of air pressure is a sign for an approaching low and is a sign for bad weather. depending upon the drop-rate (per hour) you may exspect strong winds up to a gale. The dependeny pressure-drop-per-hour > wind is depending upon the latitude. In subtropic regions it is more difficult to predict the windspeed. If the pressure-drop per hour is increasing, it is probable that a strong-wind-zone may reach us directly. In the opposite case it is more probable that the zones with strong winds will be more distant from us. Important: how is the air pressure recovering after the "valley" ? Is the pressure climbing normally or is it decreasing again ?
  

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

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.

weathertips:
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:

All informations without warranty ! 

air pressure
diurnal rhythm of air pressure

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