Monthly Tide Predictions


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For today's and yesterday's sea and weather conditions, click here.

For more information, please contact: Tony Amos at afamos@mail.utexas.edu

Information about the Tide Calendar:

The calendar shows predicted tides for the Aransas Pass Ship Channel connecting the Gulf of Mexico with Corpus Christi Bay. Other locations will soon be available. Predictions are based on a one-year series of measurements made in 1973-1974 at the Army Corps of Engineers stilling well tower which is located off the South Jetty of the Aransas Pass just east of the University of Texas Marine Science Institute's facility in Port Aransas. From the series, 37 harmonic constituents of the astronomical tide were calculated and used in a modification of the standard National Ocean Survey tidal prediction program to make hourly water level predictions and the times of the highs and lows for each day. The water level is adjusted to mean sea level rather than the Gulf Coast Datum. Consequently, the annual and semi-annual variation in sea level can be clearly seen in the position of the daily tide fluctuations relative to the zero mean sea level line (Compare January when low tides prevail with October when the opposite is true). Each hour is indicated by a vertical line connecting the curve with the zero line. In general, slack water will be at the times which the curve intersects the zero axis, but when the curve is offset as in January and October, some interpolation may be necessary. Flood and ebb tidal currents will be at a maximum at the times of high and low water respectively. This astronomical tide is often radically changed by strong winds before and during the passages of cold fronts and during extra tropical depressions. The astronomical signal will still be found "riding" on top of the meteorological surges. Past history has shown that the predicted times are quite accurate, although the range of the tides in the predictions is somewhat exaggerated. The author is working on new predictions based on a multi-year tidal series measured at the UTMSI pier (since 1985). 

Local times of the highs and lows are listed beneath each daily box (all heights are given in feet and all times are local). They are listed in "order of appearance"; if the first tide extreme is a low then the time and height will be preceded by L1, for the Low 1. Heights here are given in feet and inches. The next tide will be H1 for High 1, etc. These numbers may be difficult to read on some VGA screens. Note: the English units are given here because it is the system most commonly used by the general public. The shaded areas each day show the hours of darkness. Phases of the moon are shown for each day with the New Moon (NM), First quarter (FQ), Full Moon (FM), and Last Quarter (LQ) marked on the moon symbol where appropriate. The relative size and shape of the moon will be quite close to reality each day, but the moon's orientation is always vertical on the calendar. The author is working on a method of depicting the moon as it appears to the observer. The symbols appear on the night of the day closest to when the phase occurs, e.g. If full moon is at 1215 (24-hour clock) on the 25th of a month, then the symbol will appear straddling midnight of the 25th. Should it occur at 1145 then the symbol will appear on the 24th of the month. 

The local time zone in use is given at the top of each monthly chart. When Daylight Savings Time comes into effect in April and reverts to standard time in October is depicted by either a shorter or longer day and the symbol "CDT" for Central Daylight Time, or "CST" for Central Standard Time on the day these changes take place. Notice how it messes up a perfectly good calendar. This was one of the more difficult aspects of the calendar to program. If anyone notes any obvious errors or has any comments, please contact Tony Amos by email (afamos@utmsi.utexas.edu). Hard copies may be obtained by writing or E-mailing him a request.