14 FOUR SEASONS BREEZE | DECEMBER 2023
"Understanding the Weather" – A Series by Mel Zeldin, Retired Meteorologist
There is a lot of news these days about a developing El Niño and its
impacts on California. But what is El Niño? It is about water surface
temperatures in the eastern equatorial Pacific Ocean.
Under El Niño conditions, the waters off the equatorial areas of
South America begin to warm above average. (See picture below.)
This causes more evaporation and added moisture to the atmosphere.
Under non-El Niño conditions, the trade winds in the tropical Pacific
blow from east to west causing the circulation across the Pacific to be
clockwise in direction. This means that circulation affecting the west
coast of the United States is dominated by northwesterly flow, and
our winter storms mostly originate from off the Alaskan coast. But
under El Niño conditions, the circulation shifts to a more westerly
flow across the Pacific. In turn, this causes the storm track to become
more westerly, and this gives us more storms from the west here in
California. Such storms are generally stronger and wetter than the
typical non-El Niño storms. And as a result, we generally have a
wetter than normal winter.
However, this is not absolute certainty. Historically, El Niño
conditions result in above-normal winter rainfall most of the time,
but about 25 percent of the El Niño events do not.
What is El Niño and How Does It Affect Our Weather?
Sea surface
temperature
map of the
equatorial
Pacific
Ocean as of
September
