Chapter 3 · Try it yourself

Current Collision

Off the Northeast coast, a river of tropical water meets a stream of cold water from the Labrador Sea. You can cross from one to the other in a single day at sea. Sail the transect, spin off a warm eddy, and find out why Maine and Nova Scotia are so foggy in summer.

1. Currents

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3. Events

Sea-surface temperature, a summer day

Map of the Northwest Atlantic. Cape HatterasHatterasDelaware BayDel. BayNew YorkNYCape CodGulf of MaineG. of MaineGeorges BankNova ScotiaN. Scotia Gulf Stream Labrador CurrentLabrador C.& cold shelf water Shelf break (~200 m deep) Warm-core ring
°C: 5 cold · 12 · 20 · 25 · 29 warm
  • Gulf Stream (warm, flows northeast)
  • Cold shelf water (flows southwest)
  • Shelf break
  • Ship stations (ship = current one)

Simplified outlines and illustrative summer temperatures, not a forecast.

Station 1: Inner shelf
20 °C

  • Water at the bottom15 °C
  • Water typeShelf water
  • Fog checknot run
  • Warm-core ringnone

Slice along the ship’s track

Cross-section.

About 490 km from left to right. Depth stretched: the top 200 m take up more than half the height.

Simplified model with illustrative August temperatures (NOAA and published summer climatologies give similar ranges). Gulf Stream: leaves the coast at Cape Hatteras; averages about 6.4 km/h (4 mph) and reaches about 9 km/h (5.6 mph) at the surface (NOAA). Warm-core rings: spin clockwise, typically 50–100 km in radius, drift west-southwest about 3–5 km a day and last about two months on average; formation jumped from about 18 a year (1980–1999) to about 33 a year (2000–2017) (Gangopadhyay and others, 2019–2020). The cold pool is a band of cold bottom water left from winter that sits on the shelf from Cape Hatteras to southern Georges Bank from spring to fall (NOAA); here it is drawn below 10 °C. Fog check uses an illustrative warm, humid southwest breeze (air 26 °C, dew point 22 °C).