Tide Basics
Tides are basically long-period waves that move through the oceans in response to the forces exerted by the moon and sun. Tides originate in the oceans and progress toward the coastlines where they appear as the regular rise and fall of the sea surface. When the highest part, or crest of the wave reaches a particular location, high tide occurs; low tide corresponds to the lowest part of the wave, or its trough. The difference in height between the high tide and the low tide is called the tidal range.
Spring Tide
Spring tides occur at the time of a full moon. During this period the high tide will be higher and the low low tide lower than normal.
Neap Tide
A Neap tide will occur after the first and last quarter of the lunar month. During this period the high tide are lower and the low tides are higher than usual.
Horizontal movement of water often accompanies the rising and falling of the tide. This is called the tidal current. The incoming tide along the coast and into the bays and estuaries is called a flood current; the outgoing tide is called an ebb current. The strongest flood and ebb currents usually occur before or near the time of the high and low tides. The weakest currents occur between the flood and ebb currents and are called slack tides. In the open ocean tidal currents are relatively weak. Near estuary entrances, narrow straits and inlets, the speed of tidal currents can reach up to several kilometers per hour.
Most coastal areas experience two high tides over a 24 hour period. High tides occur 12 hours and 25 minutes apart, taking approximately six hours for the water at the shore to go from high to low, or from low to high.
Tidal Effects
The shape of bays, estuaries as well as local wind and weather conditions can combine to magnify the intensity of tides. Strong offshore winds can move water away from coastlines, exaggerating low tide exposures. Onshore winds may act to pile up water onto the shoreline, virtually eliminating low tide exposures. High pressure systems can depress sea levels, leading to clear sunny days with exceptionally low tides. Conversely, low pressure systems that contribute to cloudy, rainy conditions typically are associated with tides than are much higher than predicted. Source: NOAA.
Tide Predictions
Operating within the Australian Bureau of Meteorology (BOM) the National Tide Centre (NTC) supports climate monitoring, defence, navigation, public safety and ship operations in Australian and nearby waters. Visit: http://wwwwww.bom.gov.au/oceanography/tides/ to get the latest tide predictions for your area.
Published by NSW Maritime download the latest NSW Tide Tables for 2011-2012.