Tides and the Weather:

Forecasting weather patterns with an almanac

The Facts

  • Orbiting celestial bodies follow elliptical paths around their parent bodies, in general.

  • Each year, as the earth orbit's the sun, it makes it's close approach to the sun (perhelion) on January 3rd and is farthest from the sun (aphelion) on July 4th; while the moon comes close to the earth (perigee) every 27.5 days. These mark the times of exteme lunar and solar tidal influences.

  • This "perigee period" is two days shorter than the lunation period (from new moon to new moon), so that if the new moon coincides with the perigee one month, they are more and more out of sync on suceeding months,

    until finally the perigee is coinciding with the full moon. The result is that the perigee and syzygee (new and full moons) coincide every 206 days, when the moon's major axis is directed toward the sun. [These numbers are averages which will vary slightly over time.]

  • Due to the 8.86 year precession rate of the moon's major axis, every seventh or eighth close pass (perigee) is also a new or full moon (syzygy), bringing the moon even closer to the earth and resulting in the High Tides of the Year (on a 206 day scheduel, alternately at new and full moons).

  • Tidal peaks that occur near January 3 are exaggerated by the fact that the Earth is close to the sun at that time (in the Northern Hemisphere), and the highest tides (in the Northern Hemisphere), in general, occur close to this time when the sun's gravitational effect on the earth maximizes each year.

  • Summerizing, we can say then that the tides peak twice a day, just after our location on the globe crosses the line that connects the centers of the earth and the moon. These daily peaks, peak themselves at new and full moons when the pull of the moon is combined with that of the sun. And these monthly peaks peak when the lunar perigee (the moon's monthly close approach to the earth) coincides with either a new of full moon (called syzygy collectively) approximately every seven months. The highest of these perigee-syzygy peaks would occur at a new moon on Jan 3rd, when the sun is also closest to the earth.

    It has been suggested that this combination of circumstances represents not only the highest tides, but also times of increased probabiltiy of meteorological disturbances, such as Storms and Flooding events, the nature of which depends upon the season during which the peak occurs.

    Fergus J. Wood on Tidal Floding

    I would like to acknowledge a debt to Fergus Wood, Phd., a former Research Associate at National Ocean Survey (and later NOAA), and the author of "THE STRATEGIC ROLE OF PERIGEAN SPRING TIDES IN NAUTICAL HISTORY AND NORTH AMERICAN COASTAL FLOODING, 1635-1976", published by NOAA in 1978.

    Wood, an expert on tidal phenomena, noted that the tides themselves are not the problem, but that the problem arises when out-sized tides are accompanied by strong onshore winds. Wood pointed out that while we cannot predict whether strong onshore winds will occur within several days of unusually high tides, "The seemingly above-average frequency of such concurrent events raises the question whether some interrelationship between respective astronomical and meteorological phenomena might exist which has not yet been established".

    What I have done is to apply Wood's method to meteorological events in general, suggesting that high tides have an effect on the levels of precipitation in-land as well as along the shore lines.

    Wood goes on to say that "A certain statistical relationship also seems to hold between the most severe cases of tidal flooding and the second or third alignment of a given perigee-syzygy series. Repeated flooding events often occur within consecutive anomalistic months." [By "anomalistic months" we mean the period between the moon's close approach to the earth, which we pointed out earlier is 27.5 days.]

    What this means is that the time of the tidal peak marks the beginning of a three month period of increased meteorological disturbances, the nature of which depends on the time of year.


    Notice, in the calculator below, that the lunar perigee will coincide very closely (4 hours) with the new moon on February 28 of 2006 and the full moon on September 7 (8 hours).

    Lunar Perigee and Apogee Calculator


    To display the date, time, and distance of lunar perigees and apogees for a given year, enter the year in the box below and press "Calculate".

    Year:

    Perigees and Apogees

    The Perigee and Apogee Table

    The closest perigee and most distant apogee of the year are marked with "++" if closer in time to full Moon or "--" if closer to new Moon. Other close-to-maximum apogees and perigees are flagged with a single character, again indicating the nearer phase. Following the flags is the interval between the moment of perigee or apogee and the closest new or full phase; extrema cluster on the shorter intervals, with a smaller bias toward months surrounding the Earth's perihelion in early January. "F" indicates the perigee or apogee is closer to full Moon, and "N" that new Moon is closer. The sign indicates whether the perigee or apogee is before ("-") or after ("+") the indicated phase, followed by the interval in days and hours. Scan for plus signs to find "photo opportunities" where the Moon is full close to apogee and perigee.

    New and Full Moons

    The Moon Phase Table

    This table gives the time of all new and full Moons in the indicated year, as well as the last phase of the preceding year and the first phase of the next year.


    Winter 2006

    Looking at the perigee calculator, we see that the first alignment of this winter's perigee-syzygee series occured on February 27-8 , 2006, followed by March 29, April 27. Applying Wood's formula, we might expect repeated storm events at these times, with the most severe occuring in March and April of 2006. Note that this implies a late onset of wintery precipitation and a late spring.

    [In 2005 the January 10 perigee was within one hour of the new moon. As it turned out the January 10th peak saw records broken in California, and made Accuweather's list of Top 10 Weather Events of 2005. On the afternoon of January 10th a large portion of a bluff above the Ventura County town of La Conchita broke free, sending a wall of mud and debris onto the town below.]

    Looking at the calculator for 2005 we can see that the perigee occured 3 days after the Full Moon in October, then in November a full 6 days seperates the two; meaning that the tides "bottomed out", so to speak, in early November. In early December the perigee is 3 days before the new moon, it moved to within 2 days as of the first day of 2006, and will be just 17 hours before the new moon on the January 29-30.

    This graphic appeared on WAFF TV48 on January 24, 2006.

    Update: After the warmest January nationwide in the US, the northeast saw a record snow fall on Feb 11-2, just before the full moon, and is now seeing another storm (Feb 17-8). The local weather graphic looked like this for the upcoming week.

    Update: Posted on: Friday, March 3, 2006 12:02 PM HST, State of emergency declared for Windward Oahu; A lingering storm for the past three days has caused severe flooding and mudslides. Hawaii saw 23 inches of rain in three days.

    Update: Between Mercury's inferior conjunction to the sun on March 12 and the lunar eclipse on the 14th, we see a series of tornadoes that killed 10 in the midwest US, the first rain that Pheonix, AZ has seen in four months, snow in Flagstaff AZ, and record fires in Texas. (An inferior conjunction means that Mercury moved between the earth and the sun; a lunar eclipse means that the earth is between the sun and moon- so in a 48 hour period we saw the alignment of the sun, Mercury, the earth and the moon.)

    To review, the Highest Tide of the year occured on Feb 28th; shortly after that Hawaii sees 23 inches of rain; at the full moon before that NYC saw a record one day snow fall; at the full moon following that we see tornadoes, rain and snow in and record fires in Texas. In May New England saw the worst floods since the 1930's.


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