SAN FRANCISCO - Higher than normal astronomical tides are expected to hit the Bay Area this week and with it comes coastal advisories. We have everything you need to know to be prepared.
Coastal flooding advisories
What we know:
A coastal flood advisory impacting the Bay Area will be in effect for one week from Thursday, July 9 at 4 p.m. until July 16 at 4 a.m.
Areas along the bayshores of the San Francisco and San Pablo bays could see an inundation of up to 1.7 feet above ground level, especially in low-lying areas, shorelines and waterways.
A separate coastal flooding advisory is in effect for the Pacific Coast from Saturday, July 11 through July 15. This is in effect for the entire Bay Area and beyond, from the Sonoma Coast to Big Sur.
For both advisories, the National Weather Service says the public should not drive around barricades or through water. You should also protect flood-prone property.
Sea level rising
KTVU meteorologist Roberta Gonzales says this week's water levels will not be caused by a storm, but rather by "some of the highest astronomical tides of the year."
However, the NWS says these tides are expected to be lower than June's astronomical tides.
Gonazles points out with this type of tide, you could see flooding on a sunny day.
There is "no atmospheric river, no heavy rain, no strong wind, yet, some shoreline roads, trails and parking lots may still flood, simply because the tide is so high," Gonzales says.
In a sense, Gonzales says today's king tide is tomorrow's normal high tide.
"Scientists use these king tides as a preview of what ordinary high tides could look like decades from now as sea levels continue to rise."
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King tides flood North Bay
The king tides are peaking this time of year. In Corte Madera, some garages were already inundated, while in Larkspur, water gushed into residential neighborhoods.
Why are king tides so high?
- It's astronomical: The sun, moon, and Earth are aligned in a way that produces especially high tides.
- The lunar effect: The moon's distance and position can also enhance the effect.
- It's not all climate change: The king tides are a natural part of the tidal cycle —not caused by climate change.
Gonzales says it's important to note that over time, the king tides' starting point will change. "These naturally high tides begin reaching farther inland," she says.
Where will we see it first?
- Low-lying waterfront roads
- Parking lots
- Bay trails
- Marinas
- Beach access points
Some neighborhoods will be more vulnerable than others. Gonzales says The Embarcadero, Pier 14 and Ferry Building area often see dramatic effects when it comes to king tides.
"Saltwater can spill onto sidewalks and portions of the roadway during the highest tides," Gonzales says. "This location flooded during last month's record summer tides."
Manzanita Park in Marin County is frequently one of the first places to flood. Roads can become covered with shallow bay water.
Crown Memorial State Beach on Alameda Island is another area that is likely to see effects. Parking lots and shorelines could become inundated.
Along the Foster City Bay Trail, water can push up against levees. In Sausalito, the Bridgeway can see water ponding along portions of the waterfront during the highest tides.
These are just a few examples of how the tides may play out.
Why do scientists pay attention?
- Raising roads
- Improving levees
- Protecting wetlands
- Planning future waterfront development
Timing
Gonzales says if the forecast holds up, the evening high tides from Thursday through Sunday will be the most dramatic. "Minor flooding usually peaks within ann hour of high tide," Gonzales says.
King tides raise flooding risk along San Francisco Bay shorelines
King tides are increasing the risk of coastal flooding along Bay Area waterfronts on Friday, particularly in the North Bay.