Fluctuations in current speed can occur under the influence of 
tide-producing forces, with maximum speeds occurring daily about 9 
hours before upper or lower transit of the moon over the local 
meridian. The mean speed also appears to increase in some regions 
and decrease in others after maximum north and south lunar declina- 
tions. The current in the Miami-Cat Cay region is partly out of phase 
with astronomical forces; mean maximum speeds of 2.8 knots occur 
about 3 days after neap tides, and mean maximum speeds slightly below 
2.5 knots occur at spring tides. Regions A, B, C, D on Figure 18 
show the gradual change in surface speed across the axis of the 
current. 
Current meter measurements are sparse, but results of such 
observations are shown in Figure 18; Insets 1 and 2, composite current 
profiles in the axis of the Florida Current, show the differences in 
speed between April and August. Figure 19 shows average speeds of 
the Florida Current at various depths and distances from shore. 
Subsurface flow is similar to that shown for the surface except 
where submarine topography affects the direction of flow; the mean 
position of the axis of the Florida Current is located to the left of 
the deepest part of the channel and generally coincides with the 100- 
fathom contour around the southeast coast of Florida. 
Subsurface currents at depths less than 350 meters (1,148 feet) 
may flow over parts of the Florida reefs, while water at greater 
depths flow through the strait. In shallow depths of the Cay Sal 
region, the flow is generally northward, but at depths greater than 
100 meters (328 feet) the flow follows the direction of Nicholas and 
Santaren Channels. 
46 
