Northern California Tide Charts / Tide Calendars 2009

Although the primary forces affecting the tides are predictable enough, other factors like the irregular shapes and depths of the oceans, meteorological conditions, and coastal topography severely distort the tide wave. Meteorological conditions are the main reason for the differences between observed times and predicted times. Winds can alter both tide times and heights. For example, a strong onshore wind might increase the tide height and result in an earlier high tide. Low barometric pressure increases tide heights and high pressure decreases heights.

Actual tide times and heights can vary significantly from predicted times because of these unpredictable influences. DO NOT BE FOOLED INTO A FALSE SENSE OF ACCURACY with these beautiful charts. Time corrections for a given location are determined by averaging the observed time difference between the location and San Francisco. Time differences are generally considered to be accurate to within 20 minutes and 0.3 feet for corrections of less than three hours. While we do provide some time differences of over three hours, we ask the user to establish their credibility over several observations and to develop that all important local knowledge.

TIDE TIME CALCULATION: Tide corrections on this chart and on the following page are given in hours and minutes. A plus (+) sign means that the tide will occur later than in San Francisco. Add this number to San Francisco time. A minus (-) sign indicates that the tide will occur earlier than in San Francisco. Subtract the number from San Francisco time.

SUN AND MOON CORRECTIONS: times for sunrise, sunset, moon rise, and moon set are based on San Francisco times. For every sixty miles west of San Francisco, add 4 minutes to the time given. For every 60 miles east of San Francisco, subtract 4 minutes from the time given. For the exact rise and set time difference for any given location, make an observation. Your observed time difference from the time at San Francisco should be similar every day of the year.

Tide Heights Calculation: To find the height of a tide at a desired place, take the San Francisco height and multiply it by the ratio indicated by an asterisk (*). In the case where a correction is also given, first multiply by the ratio shown in parenthesis, then add (or subtract for negative values) the correction to the product.

For example: To find a high tide height at the Humboldt Bay Entrance, use the formula (*1.19) -0.7. Take the San Francisco height, multiply it by 1.19, then subtract 0.7 from the result. If the San Francisco height was 5.1, the height at the Humboldt Bay Entrance would be 5.4 feet (5.1 x 1.19) minus 0.7.