About Surface Analysis Charts
Surface analysis are produced manually every 6 hours and depict the locations of synoptic scale high and low pressure centers with associated surface fronts and troughs for the specific analysis time. Central pressure is depicted with 3 or 4 digits.
The term "Gale" refers to extratropical lows or an area with maximum sustained winds averaged over a ten minute period, momentary gusts may be higher ranging from 34 knot (39 mph) to 47 knots (54 mph). A "Storm" refers to an extratropical low or an area with winds sustained over a ten minute period, momentary gusts may be higher of 48 knots (55 mph) to 63 knots(73 mph) . Hurricane Force refers to a extratropical low or an area of sustained winds (averaged over a ten minute period, momentary gusts may be higher) in excess of 64 knots or higher(74 mph).
Arrows point to the 24 hour forecast positions. The term "developing" gale, storm, or hurricane force means gale, storm, or hurricane force conditions are expected by 24 hours.
The pressure analysis has a 4 millibar (mb) contour interval. In some cases especially for areas in tropical regions the contour interval may be in 2 intervals with a dashed line used. Forecast pressure values are written with 2 digits omitting the preceding 10 or 9. As an example a high pressure center with a central pressure of 1032 mb would be 32 and low pressure of 974 mb would be 74. For intense low pressure centers below 1000 mb, the analyst may use a dashed line to depict the 1000 mb isobar. By convention, isobars less than the 1000 mb dashed line are defined with an 8 mb contour interval.