Atmospheric Rivers and Storm Surges

Graphic from NOAA | post by Richard Pavek

This is the fourth installment of a research paper on the microclimates of Richardson Bay by Yellow Ferry resident Richard Pavek.

Unlike ordinary storms that circle a slowly moving Low Center passing by in a single Storm Front, Atmospheric Rivers are narrow plumes of water vapor originating from as far as the Philippine Sea that bring seemingly endless torrents of rain to our coasts and mountains. These watery plumes can be several thousand miles long and a hundred miles wide and carry as much water as the Amazon River!

A Pineapple Express is an Atmospheric River that originates near the Hawaiian Islands and extends to the Pacific coast. These are often associated with El Niños and can cause sizeable coastal flooding, or a tsunami-like phenomenon of rising water most commonly associated with low-pressure weather systems (such as tropical cyclones and strong, extratropical cyclones), the severity of which is affected by the shallowness and orientation of the water body relative to the storm’s path, and the timing of tides.

The two main meteorological factors contributing to a storm surge are a long fetch of winds spiraling inward toward the storm and a low-pressure-induced dome of water drawn up under and trailing the storm’s center. Storm surges affect Ocean Beach, Muir Beach, and Stinson Beach but do not affect Richardson Bay.

The Roiling Sea
Sea level is not level at all. Just as the Earth’s surface is not flat, the surface of the ocean isn’t flat. The great swirls of weather-driven wind moving across the ocean’s surface create hills and valleys in the sea, all the while lifting huge masses of water high into the atmosphere, later dropping them on the sea or land in the form of rain or snow. These hills and valleys on the sea’s surface are augmented by the submerged mountains and canyons far below its surface.

Superimposed on this un-level sea are the moon-driven tides! Moon tides are slow moving waves traveling across the oceans. As they progress toward the coastlines, we experience them not as ocean waves but as the rise and fall of the tides. Long tidal waves can be minimal or occasionally immense, as are the massive swells that manifest as the King Tides at Mavericks near Pillar Point, Half Moon Bay, and Stinson Beach.

The Earth’s rotational speed is approximately 1037 mph at the equator, or about 518 mph at Richardson Bay’s latitude. Fortunately, our atmosphere moves with the Earth. Because the Earth rotates to the East and the ocean responds sluggishly to rotation, the sea surface piles up along the continent’s Eastern Seaboard. Thus, the absolute sea level is lower along the West Coast of North America than the East Coast! The sea level at the Atlantic end of the Panama Canal is about 8 inches higher than at the Pacific end.