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inverse barometer effect The inverse barometer effect (IBE) is an indication of how much the tide rises above harmonic predictions when the local pressure has been lower than the seasonal average for that time and place. The effect is about 1 cm of rise for each 1 mb of pressure below average. The average pressure for US coastal waters by month is in the Coast Pilot. It varies from about 1012 to 1017 mb. A suppression of the tide height likewise happens for high pressures. See examples in The Inverse BarometerEffect in Puget Sound. Note that the Operational Forecast System (OFS) tide forecasts include the IBE so during unseasonal pressures if OFS forecasts and harmonic predictions disagree then the OFS is likely to be right, assuming the difference is about as indicated above. Wind and river run off can also affect tide height. See Operational Forecast System. Abbreviation:  IBE

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