Simple analytical expansion of monthly mean vertical ionospheric electron content (TEC) and its standard deviation (SD) is made over the American continent. TEC Faraday rotation observations at four receiving sites are used around the 75 ¿W meridian. Hourly values for each day of 1981 (high solar activity) and 1986 (low solar activity) linearly interpolated for any given sunspot number Rz allow us to use simple trigonometric functions F(t,s,g) for analytical modeling of TEC and SD. Contributions due to local time t, season-month s, geomagnetic latitude g are separated based on four nodes for t, s, g defined as 90¿¿n (n=0,1,2,3). Comparison of the present regional analytical model with International Reference Ionosphere global TEC predictions is presented. Application of the model for estimates of the monthly probability of occurrence of TEC disturbances is illustrated. The same approach can be adapted to other geographic area and/or data sources by relevant replacement of the input database, for example, using Global Positioning System-Global Navigation Satellite System observations of TEC including contributions of the ionosphere and plasmasphere. ¿ 1999 American Geophysical Union