King tides are back on the Central Coast. Here’s what you need to know
Another round of king tides is hitting the Central Coast this week.
King tides are the highest and lowest of the year, separated by less than 12 hours.
Through Tuesday, the king tides will be present twice a day: at low and high tide. On the day of the biggest sea level shift, the difference will be about 8.55 feet at Port San Luis.
Compare that to the king tides seen in San Luis Obispo County in November, when sea levels shifted a maximum of 8.1 feet.
Here’s what the king tides are predicted to look like in the Port San Luis area:
- Sunday: High tide was at 8:02 a.m. and rose to 6.7 feet above the mean high water mark. Low tide was expected to be at 3:19 p.m., with sea levels dropping to negative 1.42 feet below the mean low water mark.
- Monday: High tide will be at 8:43 a.m. and rise to 6.89 feet. Low tide will be at 4:06 p.m. and sink to negative 1.66 feet.
- Tuesday: High tide will be at 9:26 a.m. and rise to 6.78 feet. Low tide will be at 4:54 p.m. and sink to negative 1.65 feet.
What are king tides?
King tides, also known as perigean spring tides, are drastic changes in high and low tide levels that are only seen once or twice a year. They are predictable events that occur when the orbits and alignments of the Earth, moon and sun align just right.
About once every 28 days, the moon reaches a perigee, or its closest point on its orbit to Earth. All other days, the moon is further from the Earth because its orbit is an ellipse, or an oval-like shape.
When a full moon or new moon coincides with a perigee, king tides occur because the alignment causes an increase in the gravitational pull. Essentially, the higher the gravitational pull, the more drastic the tides are.
What do unusually high sea levels show?
Because king tides bring unusually high water levels to the coast, they can show what sea level rise looks like.
The ocean is predicted to rise about 0.7 feet by 2030, 1.8 feet by 2050 and 6.7 feet by 2100, according to the California Ocean Protection Council. This sea level rise will impact Olde Port Beach by 2050, and Avila Beach and Fisherman’s Beach by 2100, according to the Port San Luis Harbor District’s Sea-Level Rise Vulnerability Assessment released in September.
Sea levels are rising because of melting because of two main reasons: thermal expansion caused by warming of the ocean — since water expands as it warms — and increased melting of land-based ice, such as glaciers and ice sheets, according to the National Oceanic and Atmospheric Administration.
King tides that currently rise to about seven feet above the mean high-water mark give a glimpse into what the future may hold for the coastline, according to the Port San Luis Harbor District’s assessment.
In another decade, the mean high water mark is predicted to be at about 5.2 feet, and in 2050, it’ll be at around 6.3 feet, according to the Harbor District. Since current king tides rise above these two markers, any future infrastructure impacts from rising sea levels can be studied when the king tides come in.
By 2100, the mean high water mark may be as high as 11.2 feet, according to the Harbor District’s report, which is higher than any king tides seen so far in San Luis Obispo County.
This story was originally published December 13, 2020 at 11:02 AM.
