Weather Watch

Bang! Bang! Bang! storms ahead

For the past week, weather charts and models have been indicating a series of storms marching across the Pacific Ocean toward the Central Coast. So, get ready: stormy weather will begin tonight and continue all week.

A very intense storm developed off the Pacific coast of Russia last Tuesday. The polar jet stream brought extremely cold air from Siberia southward toward the western Pacific, while relatively warm air from the south moved northward, producing a cyclonic wind shear.

That’s like your two hands going in opposite directions as they roll over a pencil between them. The mid-latitude storms that result can be some of the most powerful on Earth.

The lower the air pressure, usually the stronger the storm that will result. When pressure drops fast enough, meteorologists refer to this explosive development as a bomb. On Tuesday, this storm became a bomb and produced hurricane force winds near the International Date Line.

Seas reached more than 55 feet in height. A very long-period northwesterly swell from this storm will arrive along our coastline on Monday.

These storms derive part of their energy from evaporation from the relatively warm Pacific Ocean. Water vapor from this evaporation condenses into clouds and precipitation, releasing latent heat.

You may have noticed that it gets warmer right before it rains. This latent heat warms the air mass, which causes it to rise further into the atmosphere. This in turn drops the surface pressure even more, which produces stronger winds.

These storms are generally driven toward the coast of western North America by the upper-level westerly wind flow across the Pacific Ocean. This wind, or jet stream, also plays a key role in the development and weakening of these cyclones through convergence and divergence in the air column.

Over the last three rain seasons, these storms have primarily moved toward the Gulf of Alaska or the Pacific Northwest, but a strengthening El Niño condition has now caused the jet stream to take a more southerly route.

In a weather pattern that reminds me of February 1998, when we had more than 15 inches of rain at Diablo Canyon and winds in excess of 60 mph, the mid-latitude westerly winds at the surface and in the upper levels of the atmosphere have dramatically increased, while the eastern Pacific high has shifted southward. In other words, this condition has left the storm door wide open for the Central Coast.

This week’s forecast

A moderate El Niño condition, increasing mid-latitude westerlies and the shifting of the eastern Pacific high southward will allow the storm door to swing wide open this week.

The jet stream is just about as powerful as they come, so exact timing of these vigorous systems will be a challenge.

The surface charts indicate three different storms moving very quickly across the eastern Pacific toward California.

The first storm will approach our area today with increasing clouds and southerly winds. Scattered rain showers will develop this morning continuing through this afternoon.

Rain, at times heavy, will develop tonight into Martin Luther King Jr. Day along with moderate gale to fresh gale force (32-46 mph) southerly winds.

Rain amounts with this storm look to generally range from about 1 to 3 inches in the low elevation regions to 2 to 4 inches in the higher terrain and mountains with snow levels from 4,500 to 6,000 feet north to south today coming down to 4,000 to 5,500 feet Monday.

After a very brief break Monday night into Tuesday morning, another wet weather system will cross the state Tuesday afternoon with a return of heavy rain and strong to moderate gale force (25- to 38-mph) southerly winds.

Another storm, the strongest of the series, will cross the Central Coast on Wednesday morning with heavy rain and fresh gale to strong force (39- to 54- mph) southerly winds. This storm could bring flood and mudslide concerns to our area.

Total rainfall amounts from these systems could add 4 to 8 inches in the lower elevations and 12 to 16 inches in the higher terrain and mountains by Friday. Showery weather will continue through the remainder of the week, with lowering snow levels and weaker winds. Thunderstorm chances will increase late in the week as a cold air mass in the upper atmosphere filters across the region. Unsettled weather is forecast for the following week.

Surf and sea report

Westerly winds of nearly 60 mph on the back side of a series of fast-moving storms will blow over an 1,800-mile-long wind fetch (distance of water over which the wind blows) out over the eastern Pacific. These winds are expected to blow across this fetch through Thursday, producing an extended period of very high swell along the Central California coastline on Monday afternoon through Saturday.

Over my 18 years of forecasting waves along the Central Coast, I’ve never seen such an extended time frame of high waves.

A 950-millibar storm developed near the International Date Line on Tuesday. A 7- to 9-foot northwesterly (300-degree deep-water) swell (with a 20- to 22-second period) from this storm will reach our coastline Monday morning, increasing to 12 to 15 feet by Monday afternoon.

This very long-period swell showed up at Hawaii marine buoys Friday.

Combined with this northwesterly swell will be increasing southerly (180-degree shallow-water) seas on Monday. In fact, these combined wave trains are expected to produce significant wave heights of 15 to 17 feet by Monday night.

A 17- to 19-foot west-northwesterly (280-degree deep-water) swell (with a 15- to 17-second period) is forecast along our coastline on Tuesday morning, remaining at this height and period through Wednesday morning, increasing to 21 to 23 feet with the same period Wednesday afternoon and Thursday morning.

Note: Combined with this west-northwesterly swell will be periods of high southerly seas through Thursday. Wave heights at the offshore buoys may reach over 30 feet during this period.

This west-northwesterly swell will decrease to 18 to 20 feet (with a 14- to 17- second period) by Thursday afternoon and night, further lowering to 16 to 18 feet on Friday.

Storm preparation tip

Pacific Gas and Electric Co. employees continuously train on how to respond quickly and effectively during an emergency, so we are prepared for the challenge of winter storms.

By participating in emergency-preparedness drills and coordinating with public safety organizations and other utilities before a storm hits, we are ready when the time comes to respond.

Here are some ways you can prepare for storms:

Simply leave a single lamp on to alert you when power returns. Turn your appliances back on one at a time when conditions return to normal.

John Lindsey is a media relations representative for Pacific Gas and Electric Company and a local weather expert. He has lived along the Central Coast for more than 22 years.