The start of another calendar year: time to print a fresh edition of the annual tide table. Inevitably its stapled pages will become tattered and dog-eared from daily use. The Saugerties Lighthouse keepers, like sailors and fishermen, live by the tides.
As part of my morning ritual while the coffee is brewing, I check the tide situation for the day, even before glancing at the weather forecast. For the benefit of guests who prefer to keep their feet dry, I scrawl the daily tide data on a chalkboard by the entryway. The ups and downs of the tide are inescapable for anyone frequenting the Hudson, and for those who live on its shores they are a daily reminder that we live on an estuary — an “arm of the sea.”
Knowing some basics about tidal forces can be pretty useful for living on the estuary. Admittedly, I learned most of my lessons the hard way.
Stationed on low-lying tidal flats, the lighthouse is twice daily surrounded by tidewater and thus becomes an island. Low tide exposes a sand bar that wraps around the stone base of the Lighthouse from the north. On the south, worn nubs of wood pilings jut out the water. With a rising tide, the sand and pilings disappear, and the lighthouse is once again an island.
The footpath leading to the lighthouse is often but not always inundated by high tide. Coming and going to and from the lighthouse requires regular consultation with the tide tables. Take the tide for granted, and damp shoes and socks will serve as a reminder for next time. My own shoes show the marks of frequent soakings.
For quick reference to check whether the tide is rising or falling, a special clock adorns the kitchen wall of the lighthouse above a regular analog timepiece. The tide clock has a single hand that sweeps around its face pointing towards high tide or low tide, or somewhere in between. The hand is geared slightly faster than the hour hand on a standard clock.
A standard clock keeps pace with the sun; a tide clock keeps pace with the moon. Unlike a 24-hour solar day, a lunar day lasts 24 hours and 50 minutes — the average between successive moonrises. This happens because the moon revolves around the earth in the same direction that the earth rotates on its axis. It takes an extra 50 minutes to for the earth to “catch up” to the moon. As the earth rotates, two high tides and two low tides occur each lunar day, with high tides occurring approximately twelve hours and twenty-five minutes apart. Thus, the sweep of the pointer on the tide clock slightly outpaces the hour hand on the standard one.
A tide clock is helpful for knowing when to expect the highest and lowest levels of the day, but says nothing of the height of the tide. As the oceans respond to the gravity of the sun and moon, the tidal range changes incrementally with the lunar phases. Around the new moon and full moon each month, when the sun and moon are aligned with the earth, the tidal ranges are more dramatic. In other words, highs are higher and lows are lower. Those high tides are enough to flood the lighthouse trail with ankle-deep to knee-deep water. Around the first and last quarter phases of the moon, however, when the sun and moon are at right angles with respect to the earth, the tides are weaker.
Local tides are also influenced by other factors. Every harbor or coastal inlet has its own assortment of tidal quirks related to latitude, longitude, water depth, and the shape of the coastline. These various influences, however complicated, are fairly consistent and predictable.
Thanks to modern software and the processing power of computers, the occurrence of high and low tide can be calculated 20 years ahead, which is a distinct advantage over what the keepers and seafarers of a century ago had at their disposal. Now, tide apps are available for smart phones, which eliminate a lot of the guesswork.
The effects of wind and weather are less predictable influences on the tide. These irregular impacts would have remained altogether baffling to me had I not been schooled by an experienced river man. During my first year at the lighthouse, while still a novice with the tides, I received an instructive email from my downstream neighbor, the professorial Dock Shuter, with the subject line “Glasco Tide Prediction Service.” It was a lesson in storm surge.
“Tide heights here are controlled more by what’s happening on the ocean than rain runoff,” he explained. “Any big winds out of the eastern half mean trouble.” Strong winds over the north Atlantic Ocean can add to the incoming tide, pushing more water upriver. Anticipating potential storm surge requires monitoring weather over the ocean.
At the risk of divulging trade secrets, here is Dock’s primary storm-surge prediction tool: a real-time tide sensor at The Battery in New York City.
Dock’s email laid out his rule-of-thumb: “It’s almost exactly six hours tidal difference between them and us. In other words, the distance from trough to peak is 100 miles. When it’s high there, it’s low here, so you can see what’s coming.”
On numerous occasions over the years, this tidbit of knowledge has helped me avoid wet feet and other tidal inconveniences. To dive deeper into this subject, there are more elaborate forecasting models. The Urban Ocean Observatory at Davidson Laboratory of the Stevens Institute of Technology developed the “Stevens Flood Advisory System,” online storm surge graphs for tide gauges in the Northeast, including several along the Hudson River.
Even with these advanced digital tools, the shifting tides can wreak havoc on a daily routine. A walk to the mailbox can quickly turn into a dance around rising water. When running late for an appointment in town, I still have a good excuse — blame it on the tides.
Patrick Landewe’s column appears monthly.
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