The point of all tidal data being approximations has been well made, and this is even before you have taken into account what the barometer is reading. High pressure will reduce your tidal heights as well as lessen the tidal rate. If you cannot go to the chore of drawing up your own graph, if you have not Reeve- F excellent publications, try using these formulae to get a rate of tide.

INTERPOLATION OF TIDAL CURRENTS
When range of tide for the day is closer to mean neaps range:
Range of tide for the day x Neaps tidal rate divided by
Mean Neaps Range

When range of tide for the day is closer to mean springs range:
Range of tide for the day x springs tidal rate divided by
Mean springs Range