Expert: Tom Whiting - 12/14/2009

Question
ok this is what I got for liberia weather.

These results were from this afternoon at 1400Z. (LIBERIAN TIME)
Temperature: 84 °F
Barometer: 29.83 ‘Hg
Humidity: 74%
Visibility: 0
Wind: 7 mph blowing from SW to NE

This is what I had for 2357Z

Temperature:77 °F
Comfort level:78 °F
Dew point:75 °F
Barometer:29.89 "Hg
Humidity:94%
Wind:5 mph from 30° North-northeast

As of now the pressure is 1012 which is about 29.89 inches of Mercury and 14.69 pound per square inch.

My question for this what are the main influencing factors for this current pressure? How does it affect wind speed and precipitation here?


Answer
Not knowing anything else, it appears that a weak  cold front passed thru your region.
1. Temperature decreased
2. pressure increased as it does after every frontal passage.
3. You received some rain from the front, raising the relative humidity and dew point temp.(original dew point at 1400 hours was probably around 70 with an RH of 74%).
4. And most telling, winds shifted from a southerly direction to a northerly direction, that's nearly always the shift you see with any cold front passage in temperate zones.  So the weak frontal zone, probably a weak cold front, changed the wind direction from southerly to northerly, and you got some showers during the afternoon hours in association with the cold front passage.  That's the best I can do with the information given. Also, this is the analysis IF you're in the prevailing westerlies region of the Earth.  If you are in the NE Tradewinds region or an equatorial region (or polar region), then all this analysis may not apply.
I've never lived at those low latitudes, so the analysis may be completely different for NE tradewinds regions.   In that case, I would just guess that a low pressure system passed just to your north, moving from west to east, accounting for the southwest to northerly wind change.
Clear Skies,
Tom