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NOAA Scientists Explain the Ocean Signs That Signal El Niño's Arrival on the West Coast

Tropical Pacific waters have already warmed over 2°C above normal, but NOAA scientists say the West Coast's own El Niño signs — Kelvin waves, fish migrations, red crabs — typically lag by months.

Step by step

  1. 1

    Trade winds weaken near the equator

  2. 2

    Kelvin waves travel east, then north

  3. 3

    Waves reach the California coast

  4. 4

    Thermocline deepens, coastal waters warm

  5. 5

    Fish and crabs shift north with warmth

Ocean temperatures off Southern and Central California are already unusually warm, but NOAA scientists say that warmth comes from a marine heat wave that predates the current El Niño, not from El Niño itself. In June, NOAA's National Weather Service declared that El Niño had developed, based on tropical Pacific Ocean temperatures near the equator that have already risen more than 2°C (about 3.6°F) above normal — but El Niño-related warming along the West Coast typically lags that tropical signal by a few months.

NOAA Fisheries scientists are watching for oceanic Kelvin waves, triggered when winds that normally blow westward along the equator weaken or reverse; the waves travel east and then north along the coast, producing sea-level changes of about 15 cm (6 inches) measurable at tide gauges and by satellite. Kelvin waves from this spring and summer first reached California in May and June, but their impact will likely be minor compared with this fall and winter, said Nate Mantua of NOAA's Southwest Fisheries Science Center.

These waves deepen the , the underwater boundary where temperature drops sharply with depth, while separate atmospheric shifts can weaken the winds that drive cold-water upwelling along the coast. The ocean effect matters more off Southern California, and the atmospheric effect more off the Pacific Northwest, said NOAA oceanographer Michael Jacox.

Migratory warm-water fish such as dorado, striped marlin and yellowfin tuna have already moved north because of marine heat waves alone, so they no longer reliably signal El Niño — a striped marlin caught off Washington in August set a new state record. Market squid, which move north in warm conditions, are also being tracked.

Pelagic red crabs, which sometimes wash up on Southern California and Pacific Northwest beaches during El Niño-linked currents, have been reported in recent months but not in the large numbers typically seen during warm events, suggesting those currents have not yet arrived.

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#El Nino#NOAA#ocean science#West Coast#climate
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