storms (Echternacht 1975). Table 3 

 shows the relationship between wet 

 season, dry season, and total annual 

 rainfall. The table illustrates two 

 important qualities of rainfall 

 distribution which are related to 

 latitude and maritime influence 

 (Thomas 1974). First, there is a 

 noticeable decrease of annual preci- 

 pitation from north to south. Sec- 

 ond, the wet-dry season differences 

 in precipitation become less pro- 

 nounced from north (mainland) to 

 south (lower Keys). Two of the 14 

 stations (denoted by asterisks) 

 report data based on six or less 

 years of record. These values prob- 

 ably do not represent the actual or 

 "true" annual averages because of 

 the brief recording period. The 

 questionable validity of these two 

 stations is further supported by a 

 five year cyclic pattern observed by 

 both Thomas (1970, 1974) and Sass 

 (1967) for the eastern coastal ridge 

 and the Florida Keys region. With 

 the stations in these two areas 

 removed from the data set, the two 

 trends described previously become 

 more pronounced. The probable cause 

 for the differences in these two 

 areas is the geographical placement 

 of the Keys and coastal islands in 

 relation to the prevailing easter- 

 lies, and the consequent effect on 

 the land-seabreeze convective pro- 

 cess. MacVicar (1981) reports that 

 the predominance of convective type 

 rainfall in south Florida during the 

 wet season results in much higher 

 rainfall totals on the mainland than 

 along the shore or on the coastal 

 islands. The distance of 1.6 km 

 (1 mi) inland from the coast can 

 mean a difference of 15% to 25% of 

 the wet season and annual rainfall 

 values. For example, the coopera- 

 tive station on Miami Beach, at 

 the water's edge, has a normal an- 

 nual rainfall of about 117 cm (46 

 inches). Seventeen (17) kilometers 

 (9 mi) inland, at the National 



Weather Service Office, the annual 

 average rainfall is 150 cm (59 

 inches) (USDC 1981a). The decrease 

 of convective influenced rainfall 

 decreases annual average rainfall, 

 and increases the percentage of dry 

 season precipitation (see Table 3) 

 to total precipitation. 



Synoptic processes (cold 



fronts) dominate the basin's dry 

 season (Echternacht 1975). They 

 occur in the area an average of once 

 every seven days (Warzeski 1976), 

 although the frequency decreases 

 equatorially (Thomas 1970). Rain- 

 fall related to these events has a 

 characteristic distribution pattern 

 distinct from that observed in con- 

 vective-type thundershowers. Synop- 

 tic rains typically fall over a more 

 uniform area of the front and are 

 dependent only on the temporary 

 passage of the system (Echternacht 

 1975). Data reported during its 

 passage would be expected to come 

 from a number of meteorological 

 stations simultaneously (Gruber 

 1969) and would be independent of 

 diurnal cycles reported for convec- 

 tive storms (Asplidin 1967). 



Wet season daily rainfall 

 patterns, which are dominated by 

 convective storms, exhibit large 

 differences in precipitation from 

 station to station (Bradley 1972, 

 Woodley et al. 1974, Echternacht 

 1975). Woodley (1970) estimates the 

 natural variability of rainfall from 

 a single cumulonimbus cloud in south 

 Florida to range from 200 to 2000 

 acre-feet; 90% of the 60 to 80 thun- 

 derstorms occurring annually in the 

 basin occur during the wet season 

 (Bradley 1972). These storms are 

 brief and usually intense, with 

 some strong winds. Day-long wet 

 season storms occur infrequently 

 and are associated with tropical 

 disturbances (Bradley 1972). The 

 short duration, high intensity 



26 



