Weather Watch

SLO County seeing the effects of El Niño even before the rains start

Local residents and members of the Los Osos/Morro Bay chapter of Small Wilderness Area Preservation (SWAP) group overlooking the Morro Bay estuary on Saturday.
Local residents and members of the Los Osos/Morro Bay chapter of Small Wilderness Area Preservation (SWAP) group overlooking the Morro Bay estuary on Saturday.

This week’s models and forecast continue to point to a strong El Niño event bringing the promise of heavy winter rains. So if this much anticipated forecast comes to pass, what type of atmospheric and oceanographic affects can we expect along our coastline?

To start, we are already seeing the consequences. Much like the 1982-83 and 1997-98 strong El Niño events, seawater temperatures are about 6 degrees warmer than normal. Usually, seawater temperatures along the Central Coast average around 57 degrees during the month of September. This September the temperature was 63 degrees.

Not only are these abnormally warm seawater temperatures bringing critters that typically thrive in tropical waters — such as the yellow-bellied sea snake found on a beach in Oxnard — and record-breaking air temperatures, they also are producing higher tides than predicted.

When the water warms, it causes thermal expansion in the upper levels of the ocean. Due to the abnormally warm waters along our coastline, the tides are running about half a foot higher than predicted.

In other words, if the tide tables predict a 6-foot high tide, the actual tide would be around 6 1/2 feet. This condition, combined with storm surge, storm runoff, and high waves can exacerbate coastal flooding and erosion.

Speaking of waves, normally along the Central Coast the biggest swells come out of the Gulf of Alaska and approach our shoreline from the northwest. This phenomenon creates a shadow zone in San Luis Bay where the Harford, Cal Poly and Avila Beach piers are located. The same condition also occurs at the Cayucos pier.

This is an important reason why these piers were built in their current locations and why they remain standing over the decades.

Those piers are usually the most sheltered along the Central Coast from damaging waves, but during strong El Niño events, storms take a more southerly route with the waves they generate coming out of the southwest.

This is what happened on March 1, 1983 when El Niño-driven storm destroyed the 2,700-foot-long wooden Unocal pier in Port San Luis. It was later replaced with a steel-and-concrete structure in 1984, which became the Cal Poly pier.

The rains also have an effect on the salinity levels of our bays and estuaries.

Since 1950, strong El Niño events on average have produced 140 percent of normal rainfall. About a decade ago, we deployed an InterOcean S4 Current Meter in Morro Bay to see how fast the tides drove the water in and out of the bay. It also measures water salinity.

Looking out over the estuary, it’s fascinating how quickly it changes from a brimming body of water during high tide to silvery mud flats at low tide. The Central Coast usually experiences two high and low tides per day, but due to the tidal cycle being over 24 hours, some days have only one high or low tide.

Hence, two flood and ebb tides occur per day as the seawater flows in and out of the estuary. In mid-December 2006, over 8 inches of rain fell in just four days. Despite 6-foot-plus high tides over that time frame, the water flowed continuously out to sea through the bay’s mouth.

In other words, the salty ocean water didn’t flow in. Consequently, the salinity level sensors on the S4 current meter indicated a significant drop in the saltiness in the bay.

Since December 2010, we haven’t seen significant flooding along most of coastal regions of San Luis Obispo County. If the water flow rates increase to flood levels in San Luis Obispo Creek, golf balls are sometimes dredge from the shores of Avila Beach Golf Resort and deposited on the beaches of San Luis Bay.

As I said before, El Niño does not guarantee above-normal rainfall, but, historically, the stronger the El Niño event, the higher the probability of it.

The last major El Niño storm season in 1997-98 created widespread flooding and caused power outages impacting more than a million PG&E customers. PG&E has been preparing for storms like those by practicing for extreme-weather events and natural disasters; using advanced meteorology tools to forecast where storm impacts will be most significant; and adding innovative technology to its electrical grid.

PG&E also urges its customers to be ready for natural disasters. That includes creating a family emergency plan and creating emergency kits for your home, your office and your vehicle. PG&E offers emergency-preparation tips on its website at http://www.pge.com/en/safety/preparedness/index.page

  Comments