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The North Wall….

The North Wall…. Picture Source: “The Perfect Storm”. NORTH WALL EFFECT. Extreme Winds & Seas. Cold Air Flow. AT: 21 o F. 53 o F. 75 o F. North Wall. Land. Cold Water. Gulf Stream. 2 NM. North Wall Effect. Typically a cold season event

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The North Wall….

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  1. The North Wall…. Picture Source: “The Perfect Storm”

  2. NORTH WALL EFFECT ExtremeWinds& Seas ColdAirFlow AT: 21oF 53oF 75oF NorthWall Land Cold Water Gulf Stream 2 NM

  3. North Wall Effect • Typically a cold season event • Creates high, steep seas, in and near the Gulf Stream • Effects usually confined to a small area • Quick to develop (Explosive) • Two types • Perpendicular flow (NW) • Opposing flow (NE) Rogue wave estimated at 60 feet moving away from ship after crashing into it a short time earlier. In the Gulf Stream off of Charleston, South Carolina, with light winds of 15 knots.

  4. Perpendicular flow • Cold Air Flows Over Warm Water • minimum 20 degrees (F) temperature difference required • common with cold air outbreaks over central Atlantic coast • Dramatic temperature gradient in the vicinity of the Gulf Stream results in • higher winds speeds on and near surface • Higher Surface Winds = Higher Waves • Worst area is where Gulf Stream is closest to land (i.e. Hatteras) • Dramatic temperature gradient in the vicinity of the Gulf Stream results in • higher winds speeds on and near surface

  5. PERPENDICULAR WIND FLOW Air Temp: 45 Deg SFC Winds: 30 kts Max Winds 45 kts Gusts to 60 kts North Wall Hatteras Gulf Stream South Wall 20 ft Ts - 75 Vs - 3 •Air is less modified and features extreme gustiness•Effects felt further seaward•Often occurs with explosive cyclogenesis 15 ft

  6. OPPOSING WIND FLOW • Northeast winds flowing over a northeastward moving current • Generates very high, steep waves over a fairly narrow zone • Temperate contrast not as important • Typically occurs with a stalled front off the mid-Atlantic coast, or nearly stationary Newfoundland Low • Common with developing “Hatteras” storm force low • Generates very high, steep waves over a fairly narrow zone The mast visible on the starboard side is 25m above sea level, and the wave is breaking from behind the ship. The wave was at least 20m high, perhaps 30m (since its trough, as well as crest, would be lower than other waves).

  7. Air Temp: 45 Deg SFC Winds: 30 kts OPPOSING WIND FLOW Max Winds 40 kts Gusts to 55 kts North Wall 15 ft 15 Gulf Stream 15 Hatteras 32 20 South Wall 22 15 Vs - 3 15 •Wind fetch opposes Gulf Stream•Narrow zone established with steeper waves•Not dependent on season Ts - 75

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