Central Coast Weather: Hawaiian Trade Winds Point To La Niña



PG&E meteorologist John Lindsey took these photos of the seas generated by the trade winds off Maui, Hawaii.

Our family visited the Hawaiian Islands earlier this month, and the easterly trade winds blew hard and continuously throughout the day and night.

These winds can provide an indication of a neutral or La Niña condition, and here’s why.

The trade winds were named for their ability to quickly propel merchant ships across the ocean.

Unlike the capricious winds of the central coast, where one day you may have Santa Lucia (northeast) winds in the morning, coming out of the northwest in the afternoon or southerly winds before the arrival of ‘a cold front, the trade winds blow continuously from one direction for months in a row. In other words, they are highly predictable.

When these trade winds become weak or especially when they come out of the west, it is the sign of an El Niño event.

Typically, during non-El Niño years, the lower pressure resides near Darwin, Australia. Meanwhile, about 5,000 miles east and across the date line, higher pressure is present over French Polynesia.

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PG&E meteorologist John Lindsey took these photos of the seas generated by the trade winds off Maui, Hawaii. John lindsey

This condition, combined with the Coriolis effect, produces easterly trade winds in the equatorial regions of the Pacific Ocean and pushes warmer sea surface waters westward while creating upwelling seawater. and colder seawater temperatures in the eastern Pacific basin.

For reasons that we do not understand, the pressure difference between northern Australia and Tahiti is weakening.

This, in turn, causes the easterly trade winds to diminish or even reverse from the west. As a result, near-surface ocean currents decrease or retreat eastward, producing warmer seawater temperatures along the west coast of South and Central America, and when they are sufficiently forts, California.

Judging by the strength of the trade winds in Hawaii, it is no surprise that the Federal Center for Climate Prediction issued a watch for La Niña in the midst of our next rainy season, from November 2021 to March 2022.

What is La Niña?

So what is La Niña? It’s mainly ocean temperatures and how the atmosphere reacts to them.

Since 1950, the The National Oceanic and Atmospheric Administration (NOAA) used sea surface temperatures to categorize the amount of temperature that deviates from the mean.

NOAA uses Niño 3.4, a region of sea surface temperatures (SST) in the central equatorial zone of the Pacific Ocean, as the standard to classify El Niño (SST warmer than normal) and La Niña (SST cooler. than normal) events.

Divinatory SST cycles in Niño 3.4 are categorized by their deviation from the average SST over a three-month period.

The Southern El Niño Oscillation (ENSO) moves through the El Niño, Neutral, or La Niña classification cycles at approximately an annual frequency.

Neutral or weak conditions in La Niña and El Niño generally do not produce reliable seasonal precipitation forecasts along the central coast, but a moderate, strong, or very strong Niño or La Niña classification does so more often than not.

Overall, moderate to heavy La Niña conditions generally produce below average winter precipitation. However, there have been a few La Niña years that have produced far above average amounts of precipitation.

So how do these above or below average sea water temperatures in such a remote area have such a profound effect on the weather in California?

The answer is in the winds, or, should I say, the high winds.

During an El Niño, the warmer waters of the eastern Pacific produce more evaporation.

As this water vapor rises in the atmosphere, it often condenses into thunderstorms and releases enormous amounts of latent heat, further lowering atmospheric pressure.

This zone of low pressure alters the trajectory of the southern branch of the polar jet stream, pulling it further south towards the central coast. This condition, in turn, brings storms that produce valuable rain and snow.

La Niña does the exact opposite. It tends to push the storm track farther north in the Pacific Northwest, leaving the central coast with fewer storms.

The Hawaiian Trade Winds Waves 2.jpg
PG&E meteorologist John Lindsey took these photos of the seas generated by the trade winds off Maui, Hawaii. John lindsey

What about climate change?

How is climate change taken into account in ENSO?

First, many climatologists are surprised by the number of records of high temperatures that have dropped despite being neutral or La Niña in recent years.

La Niña produces a greater amount of upwelling and acts as a gigantic air conditioner for the Earth.

Second, these warmer temperatures lead to the intensification of the global water cycle, which is believed to produce more prolonged droughts, but more intense rainfall.

As the air warms, its ability to hold water vapor increases, increasing the risk of flooding.

As severe as the current drought is, and it is terrible, I’m more worried about more extreme rainfall events and the flooding they can produce. This was illustrated recently when unprecedented heavy rainfall resulted in flooding in Germany and Tennessee.

According to the National Weather Service, up to 17 inches of rain was recorded in 24 hours in Humphreys County, Tennessee, breaking the previous daily state record of three inches!

PG&E Message

The wheels of the bus are still spinning in circles, but in several communities in northern and central California, school buses will soon be supplied with clean electricity.

PG&E is helping school districts in its service area with their transition to electric buses, promoting cleaner air, lower maintenance costs and quieter trips.

Through its EV Fleet program, PG&E is working with more than 30 school districts by adopting approximately 350 electric buses. For more information, please visit pgecurrents.com.

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